Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. BULLETIN OF THE Be) USDEPARDENT OF AGRE No. 98. Contribution from the Bureau of Animal Industry, A. D. Melvin, Chief. August 14, 1914, (PROFESSIONAL PAPER.) THE APPLICATION OF REFRIGERATION TO THE HANDLING OF MILK. | By Joun T. Bowen, Technologist, Dairy Division.. INTRODUCTION. In the following pages an attempt has been made to discuss briefly the various applications of refrigeration, both when employing ice and refrigerating machinery, in the operation of the modern milk plant, creamery, or dairy, and to discuss in each instance the methods most commonly used in the latest and best equipped plants. While refrigeration has made considerable advancement in dairy- ing in the last few years, even more progress could have been made had more owners and operators of milk plants, creameries, and dairies been fully aware of the many advantages to be derived from the use of proper refrigeration. It is further believed that the manufacturers of refrigerating machinery are not familiar with the special conditions existing in this industry. Therefore the object of this bulletin is to be of service to the manufacturer of refrigerating machinery as well as to those employed in the dairy industry. It is not intended to give in detail the size and arrangement of refrigerating equipment necessary in plants of various capacities, as the conditions vary to such an extent that to do so would be impossi- ble, but to state briefly the elementary principles of refrigeration and refrigerating machinery and to describe what is recognized as the best and most modern practice in the industry and to leave the details in each case to those on the premises, who are better able to judge and to modify the suggestions given herein to suit the existing conditions. It is a well-known fact that heat and cold perform very impor- tant duties in handling milk and milk products. In pasteurizing milk Note.—Discusses the application ofrefrigeration in the operation of the modern milk plant and describes the various forms of mechanical and other systems of cooling. Of interest to procucers, shippers; dealers, and consumers of milk generally, and also to manufacturers of refrigerating machinery and appliances. 40083°—Bull. 98—14—_1 2 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. heat is used to destroy the bacteria, or at least to reduce their num- ber to such an extent as to prevent their producing disease; but pas- teurized milk as well as unpasteurized market milk should be cooled to a temperature of 50° F. or below and held at this lower tempera- ture until used. At a temperature below 50° F. bacteria multiply less rapidly, but between 50° and 100° F. the increase is very fast; hence the necessity for thorough cooling and the maintenance of low temperatures until used. DEFINITIONS OF TERMS. A knowledge of the terms used in refrigeration is necessary in order to better understand the matter given in the following pages. There- fore definitrons of the principal terms and units employed are given for the benefit of those not already familiar with them. British thermal umit.—A British thermal unit (B. T. U.) is the quan- tity of heat required to raise 1 pound of pure water 1 degree Fahren- heit, at or near its maximum density, 39.1° F. Some authorities consider a British thermal unit as the heat required to raise 1 pound of pure water from 61° to 62° F. For practical purposes, however, it may be considered the heat required to raise the temperature of 1 pound of water 1 degree Fahrenheit. Sensible heat.—Sensible heat is the heat that may be felt by the hand or measured by a thermometer. Latent heat.—Latent or *‘ hidden”’ heat is the heat which is expended in molecuiar work of separating the molecules of the substance and can not be measured by a thermometer. Every substance has a latent heat of fusion, required to convert it from a solid to a liquid, and another, latent heat of vaporization, required to convert it from a liquid to a gas or vapor. Thus, if heat is applied to a pound of ice at 32° F.it will begin to melt, and no matter how much heat is applied the ice will not get any hotter. After every particle of ice has melted, we will have 1 pound of water at 32° F., the same temperature as the ice before heat was applied. Experiments have shown that it requires 144 British thermal units to melt 1 pound of ice at 32° F. into water at 32° F.; hence the latent heat of fusion of ice is said to be 144. If heat is applied to 1 pound of water at 212° F., the water will remain at 212° F. under atmospheric pressure until all of it has been evaporated into steam at 212° F. This has been found to require 970.4 British thermal units; hence the latent heat of vaporization of steam at atmospheric pressure is said to be 970.4 B. T. U. Specific heat.—The specific heat of a substance may be defined as the ability of that substance to absorb heat compared to that of water. Water being one of the hardest of all substances to heat, its specific heatis taken at unity. Therefore the specific heat of other substances is usually less than unity. A better understanding of latent and spe- | APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 3 cific heat may be had by studying the diagram in figure 9, on page 24, which shows graphically the relation of heat to Geraperatire: Ton refrigeration.—Refrigeration, or ice-melting capacity, is a term applied to represent the cold produced, and is measured by the latent heat of fusion of ice, which is 144 B.T.U. per pound. In other words, it is the heat fequiced to melt 1 pound of ice at 32° F. into water at the same temperature. The capacity of a machine in tons of ‘‘ice melting” or “refrigeration” does not mean that the machine would make that amount of ice, but that the cold produced is equivalent to the melting of the weight of ice at 32° into water at the same tem- perature. Therefore 1-ton refrigeration is equal to 144 x 2,000, or 288,000 B.T.U. A 1-ton refrigerating machine is a machine that has a capacity sufficient to extract from an insulated bath of brine,200 B. T. U. per minute, 12,000 B. T. U. per hour, or 288,000 B. T. U. per 24 hours. Absolute pressure.—Absolute pressure is pressure reckoned from a vacuum. Pressure gauges in general use are arranged to indicate pressure in pounds per square inch above atmospheric. To convert gauge pressure to absolute pressure, 14.7 pounds, the weight per square inch of air pressure at sea level, must be added. CHANGES IN MILK CAUSED BY TEMPERATURE AND TIME. PHYSICAL CHANGES IN MILK AT LOW TEMPERATURES. During the last decade the progress made in the physical, chemical, and bacteriological studies of milk and its products has greatly mod- ified the various dairy operations and has led to improved methods of treating and handling dairy products, based mainly on the appli- cation of the two extremes, heat and cold. The preservation of milk and its products depends singe entirely on the use made of these two factors. In this bulletin, however, we will discuss only the use of refrigeration as a means of preserving dairy products. Before dis- cussing the practical application of refrigeration to the dairy industry it is advisable to make a short summary of the data at hand relating to the physical, chemical, and bacteriological changes and modifica- tions which the action of cold produces in milk. SPECIFIC HEAT. In view of the wide variations in the specific heat of milk and cream, as found in the limited amount of literature on the subject, the United States Bureau of Standards was requested to make determinations of the specific heat of whole milk and single and double cream. Sam- ples of milk and cream, approximating average conditions, were pre- pared by the Dairy Division laboratories and forwarded to the Bureau of Standards in the afternoon, placed in the calorimeter and packed 4 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. in ice until the next morning when observations were begun. The chemical analyses of the samples were as follows: 34 per cent milk: 12.68 per cent total solids, 9.18 per cent solids not fat, 87.32 per cent water; 20 per cent cream: 27.27 per cent total solids, 7.27 per cent solids not fat, 72.73 per cent water; 40 per cent cream: 44.30 per cent total solids, 4.30 per cent solids not fat, 55.70 per cent water. In view of the fact that only a single test on one sample of the material was made the results can be considered only as tentative and not final. TaBLE I.—Specific heat of milk and cream. 20 40 | 20 | 40 Temperature. Milk. | percent | percent | Temperature. Milk. | per cent | per cent cream. | cream. cream. | cream. ls aC: colt SC 35. 6 ZAR eae cae OSSSn| sate sect 95.9 35.5 0. 93 0. 89 0. 86 37.4 3.0 ECP Baseeenade 0. 83 100. 4 38:0" |neses cseacl esos eee 43.7 6.5 92 91 - 90 105. 8 41.0 92 OY |osaek Bees 48, 2 O70 Receece=-= WF loacogsese 109. 4 43310: || eecteMooc| Sasa ee 78 51.8 11.0 WB) soeee aaeke - 96 114.8 AGS Oli = eet SY he! | Se eee ae 55. 4 Ibs ese ccansee OF alison 118. 4 48.0 oe eB eeseeerc 78 59.0 15.0 94 95 1.02 123. 8 SLAOn Cee eS! 861 ease Aet et 66. 2 19.0 95 1.01 1.07 127.4 DONOM oer arsteners tcmrse relat ol. 71.6 22.0 - 94 BOD aceione sce 131.0 55. 0 93 862s 75. 2 DATO Resets ote seats | stesso 93 136. 4 5850) ees osese | Sora seeraee 76 78.8 26.0 UB ececpuaeac - 88 141.8 61.0 93 ofl esa Se 82.4 2OA0E arr so = 3; = “4 =) — pe se t ARN Ih es LOIS riglse SIS VE ayes WWI S0 0 NY eS i Q - oh 7, to 20° F.; 0:623><0.5(82—20). 0.205528 3 ee eee ee 4 723 The total heat, therefore, that must be removed in cooling the 1,000 cubic feet of air under the above conditions is 885 + 723 =1,608 B.T.U. In the case of cold storage the total amount of refrigeration required for air cooling depends, of course, on the number of times the air in the room is renewed in a given oe With the indirect-air system usually employed in the dairy industry the same air is kept in circulation to a great extent. Tn all cold-storage work the air in the rooms must, of course, be cooled, but as the refrigeration required is generally small compared with that necessary for cooling the goods and in taking care of the heat that comes through the walls, floors, and ceiling, it is usually ignored and a liberal allowance made to cover this as well as lighting, presence of workman, poor workmanship, and other factors. INSULATION. The word “insulate” is derived from the Latin word ‘insula,’ meaning “island.” Therefore the significance of the definition of insulate is: To place alone or in a detached situation; separated by a nonconductor from other conducting bodies; having no communi- cation with surrounding objects. Hence insulation in a cold-storage room is applied on the interior surface of the outside walls, under the roof, and under the lowest floor, to prevent, as far as possible, the transfer of heat from exterior heat-conducting bodies like the air and the ground. With the increased application of refrigeration the problem of properly insulating the walls, floors, and ceilings of the cold-storage rooms is of the greatest importance and should be considered in the light of a permanent investment along with the building and equip- ment, the returns on which should be based on the saving effected by the (oer operating cost. It is evident that after the goods 1 in storage have once been cooled to the desired temperature, it is then merely a question of supplying 40083°—Bull. 98144 F 50 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. sufficient refrigeration to take care of the heat which finds its way through the insulation of the walls, floors, and ceilings of the cold- storage rooms. The greater the efficiency of the insulation the less heat will get through from without. There is a limit, however, to the amount of insulation that should be installed, which is the point where the interest on the money invested in insulation, the repairs and depreciation on same, balances the saving in operating expenses. There is no material known that will entirely prevent the passage of heat. However, there are some which offer a very high resistance, and are therefore termed nonconductors or insulators. The best heat insulators appear to be those that contain the greatest amount of entrapped air confined in the smallest possible air space. The function of cold-storage insulation, then, is to prevent the outside heat from passing through the walls, floors, and ceiling into the interior of the cold room. Therefore the problem is to minimize the passage of heat by interposing in the walls, floors, and ceiling a material or construction which will resist the transfer of heat from the outer to the inner side of theroom. The materialsmost commonly used for this purpose are the different varieties of cork products, mineral wool, hair felt, rock wool, vegetable fiber, sawdust, mill shavings, etc., used In combination with wood, cement, masonry, and air spaces. At one time it was common practice in the construction of buildings for cold-storage purposes to provide a series of air spaces in the walls, some of which were as much as 12 inches wide, the supposition being that they were dead-air spaces. As a matter of fact they were not. As the air in contact with the warmer surface became heated it rose, while that in contact with the cooler surface fell, thus producing a circulation tending to equalize the temperature of the sides of the airspace. Dead air, however, is a good nonconduc- tor, but unless the air spaces are properly proportioned, the above- mentioned air currents will be set up. Therefore, it is the present - practice to fillin the spaces with some porous substance to break up the space into an indefinite number of small dead-air spaces which will effectually prevent circulation of the entrapped air. On the other hand, there is danger of packing the insulating material too closely, which will result in favoring the conduction of heat through the walls. Sawdust and mill shavings are mentioned in the above partial list of insulating materials, but they are not to be considered among the best. They can be had in any part of the country, and often without cost, andif kept dry are good insulators. Itisa very difficult problem, however, to keep them dry, and when used, great care should be exercised in the construction and workmanship of the walls in order to keep out the moisture, | APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 51 Planing-mill shavings are better for insulating purposes than sawdust. They are elastic, do not settle rapidly, and will not absorb moisture as readily as sawdust, and, most important, can usually be had in very dry condition. They should be odorless, free from dirt, bark, and chips, and should be well packed into place to prevent future settling. About 9 pounds per cubic foot is considered the proper density to which they should be packed. Sawdust has in the past been used to a great extent in rural dis- tricts for insulating the walls of small cold-storage buildings, due to the fact that it is available in most country districts, and generally may be had without cost. It is not a satisfactory material, however, for insulating purposes, as itis always more or lessdamp. The damp- ness not only destroys its insulating value, but it favors the growth of molds and bacteria, first in the sawdust itself and then in the walls of the building. The rotting and the consequent heating causes the sawdust to settle and leaves open spaces, which further weaken the insulation. It also furnishes an ideal nesting place for rats and mice, and the tendency of these rodents to carry matches into their nests and to start fires is well known. When sawdust or mill shavings are to be used they should be thoroughly dried before being put into the walls. _ Furthermore, if air is allowed to circulate in the shavings or sawdust moisture will be deposited in warm weather, and then, again, in cold weather it will dry out. This being repeated for several years will cause the boarding and shavings to rot. If, however, the shavings or sawdust is surrounded by waterproof paper and boarded, the con- densation will not occur and deterioration will be prevented. In deciding upon an insulating material for cold-storage purposes | the following points should be carefully considered: Efficiency as a heat insulator; whether or not it will retain its efficiency indefi- nitely; structural strength; the effect of moisture; uniformity of insu- lating value; whether fireproof or not; space occupied; first cost; cost of installing, etc. | The greater portion of the refrigeration required for cooling cold- storage rooms is done to remove the heat that leaks through the walls, floors, and ceilings, and only a small part is required to cool the goods in storage. As previously stated, it is necessary to pump out, so to speak, the heat that enters from the outside after the goods are once cooled to the desired temperature. Take for example a creamery cold-storage room 10 by 10 by 10 | feet, inside dimensions, which is of sufficient capacity to hold a | week’s output of butter from a creamery making 2,000 pounds daily. | The butter will come from the churn at approximately 58° F. The | average outside temperature of room is assumed to be 75° F., and the | inside temperature 32° F. It is further assumed that the walls, floors, and ceiling are insulated for a heat transmission of 3 B. T. U. 52 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. in 24 hours per square foot per degree difference of outside and inside temperatures of the room. The total surface of the room is 600 square feet. Then; Bi. U: The heat that will leak through mto the room in 24 hours is 6003 (75-32).. 77, 400 The heat to be removed from the butter is 2,0000.5494 ! (58-32). ......... 28, 574 Total heat that will have to be removed.......-.........--..2------ 105, 974 From the above figures it will be noted that practically three- fourths of the refrigeration required in the average cooling room is done to remove the heat that leaks in through the insulation. Hence the necessity for good insulation. It would seem from the foregoing that the more insulation put into the walls, floor, and ceiling the better, which is true when viewed from the standpoint of the refrigerating machine, as the more and better insulation used the less work the machine will have to do. But as insulation is expensive, a point is soon reached where the interest on the money invested, repairs, and depreciation on the insu- lating material balances the saving in reduced machine capacity and operating expenses. By installing more and better insulation, the saving in the capacity of the refrigerating machine is an item of considerable importance and one that has not been given the atten- tion that it justifies. From the data at hand, it appears that the most economical point to insulate for is a transmission in 24 hours of 2 B. T. U. per square foot per degree difference of outside and inside temperature of room, when the average outside temperature is 70° F. and the inside tem- perature of the room is 32° F. With an average outside temperature of 70° F. and an inside temperature of 0° F., the economical point is about1$B.T.U. Inview of thefact that dairy products are extremely perishable when held at a temperature of 60° F. or above, the added security which the lowest heat transmission affords in order to hold over temperatures in case of the machinery breaking down, or where the plant is operated during the day only, makes the increased invest- ment in insulation desirable. Good insulation not only permits operating the plant with the least refrigeration, power, time, and cost, but also helps to reduce fluctuations in room temperature. After shutting down the refrigerating plant the inflow of heat con- ‘tinues, but at a constantly decreasing rate. With a properly insu- lated room it will be several days before the inner air temperature will be near that of the outside temperature. As an example of the saving effected by good insulation, take two cold-storage rooms of the same size and construction, say 10 by 10 by 10 feet. The walls are assumed to be built of brick 13 inches 10. 5494 specific heat of butter. APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 30 thick, the floors and ceiling of concrete slabs 5 inches thick, the floors resting directly on the ground in both cases. The inside temperature of the two rooms is held at 30° F. by refrigeration and the average outside temperature is assumed to be 70° F. for 90 days. Suppose one building is not insulated at all and the other is insulated for a heat transmission of 2 B. T. U. per square foot of surface per 24 hours for each degree difference between inside and outside temperature. The heat transmission through the 13-inch insulated brick walls is taken as 11.3 B. T. U. per square foot per degree difference of inside and outside temperature in 24 hours, and that for the 5-inch con- crete slabs forming the floor and ceiling 28.8 B.T. U. In view of the earth offering a certain amount of protection to the floor slabs, which were assumed to rest on the ground in both cases, only lralf of the temperature difference between the outside and inside air is taken in computing the heat transfer through the floor in the uninsulated room. Then, for the uninsulated room the transmission will be: Bes Ue prrelewariss400 rls (70-30) X90) 2 eo eb eke cee eee 16, 272, 000 Wena OO ><78: 87 (10-30) X90 se ee ele oe ee see 10, 368, 000 lear mO0p<2525.( 00-30) )><90 22.2 el eee ea Se ee 5, 184, 000 Total heat transmitted through the walls, floor, and ceiling........ 31,824, 000 31, 824, 000 388, 000 =110.5 tons, This is equivalent to Therefore there will be 110.5 tons refrigeration required to remove the heat which comes through the walls, floor, and ceiling, and assum- ing that it cost $1 per ton to produce the refrigeration, it will amount to, in 90 days, 110.5 xX 1 =$110.50. Now, in the case of the insulated building we have: Earle weiles 20 -2001020) X90. 262 ee le 2, 880, 000 Seiten OO ON (IO=30) 00 <- ee eee 720, 000 Pigue’ UND, (7-0) SRO re 720, 000 Total heat transmitted through the walls, ceiling, and floor........ 4,320, 000 4, 320, 000 288, 000 3 At a cost of $1 a ton for the refrigeration, it will amount to 15X1=$15. Therefore, there will be a loss of $110.50—$15=$95.50 on the uninsulated building in 90 days. It will cost approximately 40 cents per square foot to insulate the above-described building for a heat transmission of 2 B. T. U. per square foot per degree difference of outside and inside temperature per 24 hours, or a total of 600 x 0.40 =$240. Consequently the insulation would pay for itselt in about seven and a half months’ operation. Equivalent to —=15 tons. 54 BULLETIN 98, U. S, DEPARTMENT OF AGRICULTURE. As before stated, in order to obtain the maximum economy from a cold-storage plant, it is necessary that the investment and operating expenses should be so balanced that their sum is a minimum. The refrigerators or cold rooms may be constructed with a small amount or poor quality of insulation, requiring only a comparatively small investment, but on the other hand this saving must be offset by machinery of greater capacity and consequently more expensive both in initial cost and in the cost of operation. There is, however, a possibility of investing too much money in insulation, so that the fixed charges on same may be greater than the corresponding saving in investment in machinery and in operating expenses. Generally speaking, the cheaper the insulation the more should be used, and also the more expen- PT tT ttt tt tts | T/L |] sive the refrigeration dd deeded TolsZloa the more insulation $190 72 . z should be installed. cob CT PTT tm onder to deter gy fe a ee FBS /|_| | | | mine the relative X ook PRC gt peters amount of refrigera- . tion and insulation £ cod 4s to be used to obtain : 5 the greatest saving, Scokas it is necessary to con- 6 ; sider the cost per ton 3 Bee of refrigeration; the Of. YA one 74a eeeee a Ny | sh alah ed Ol Spe ay Cie Rae Fe ee Fig. 22.—Economics of insulation. cost per square foot of insulating mate- rial; the repairs and depreciation on insu- lating material; the insulating value of the material; the temperature maintained inside of room; and the average outside temperature. The curve in figure 22 is based on the above-mentioned variables, which are assumed to be as follows: Cost per ton of refrigeration. Cost per square foot of insulation, 1 inch thick, installed, $0.10. Repairs and depreciation of insulation material, 15 per cent. Insulating value of material per board foot per 24 hours for each degree difference between the inside and outside temperature of room, '8 Bo TU; Inside temperature of room, 30° F. Average outside temperature of room, 70° F. There is also shown a curve calculated from an inside room tem- perature of 0° and ar average outside temperature of 70° F. APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 55 To use the curves in figure 22, suppose it costs $1 per ton per 24 hours to produce the refrigeration, and it is desired to know the amount of insulation that will give the maximum economy when the inside temperature of the room is at 30°F. and the average out- side temperature is 70° F. Look on the left-hand side of the figure, under “Cost per ton of refrigeration,’’ and follow the horizontal line opposite $1 until it crosses the curve marked ‘Maximum economy, 30° te 70° F.,” then read at the bottom directly under the point where the curve cuts the horizontal line indicating $1 per ton, and it will be found to require 3? inches of insulation. If the inside tem- perature of the room had been 0° and the average outside tempera- ture 70° F’., the thickness of insulation required to obtain the maxi- mum economy would have been 4? inches. Then the estimate cost of insulation per square foot is found by projecting a line vertically through the intersection of the curves and the horizontal line indi- cating a cost of $1 per ton of refrigeration, until it cuts the straight line marked “Cost of insulation per square foot,’”’ then reading on the left opposite this point and under “Cost of insulation per square foot,’’ the cost per square foot of insulation is found to be 374 and 474 cents, respectively. Itis assumed that the cost per square foot of insu- lation will be a constant in small cold-storage rooms of the size com- monly used in milk plants. In the economical operation of a refrig- erating plant the insulation is the most important point and great care should be exercised in its selection and installation. All exposed piping between the expansion valve and the suction side of the machine should be carefully insulated, as well as the walls of the refrigerator itself. In the building of cold-storage rooms or boxes there is often used a construction of boards in combination with air spaces, and while cheap in first cost, in a few months in extreme cases the walls will begin to deteriorate and show increased losses. In a short time the piping in the box or room is not sufficient to hold the temperatures, and finally the capacity of the machine is not enough to do the work; whereas, with a sanitary box properly constructed of nonabsorbent material, no deterioration will occur after long and continued use. Consequently, it is very important wherever possible to eliminate wood in the construction and substitute for the walls hollow tile or brick. When placing the insulation in the walls, floor, and ceiling of cold- storage rooms it is of the utmost importance that the workmanship be of the best. The insulation should be continuous. There should be no break in continuity where floor, walls, and ceiling meet. Each course of insulation should be well set up before the next course is put in place. In all cases the blocks of insulation should fit tightly 56 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. together. No cement should be used in the joints, but only on the back of the blocks. The floors should be of concrete and should preferably be laid solidly on the insulating material. The insulating blocks should be laid in asphalt and coated over the top with hot asphalt and then 2 inches of concrete laid directly on the insulating material and finished with a coat of 1 inch of Portland cement. In cold-storage rooms designed for storing milk and milk products an insulation should be used that will take a waterproof interior finish, such as Portland or other hydraulic cement, or ee vitrified hollow tile laid up | aren \avo mm cement mortar. This %Boarvs construction permits of hee 2 riTcH 425 1 Fee 2 } being thoroughly washed Be out with either hot or cold ta/sPaee eae water without injury to it 1g SPRUCE or to the insulation proper. Te BOARDS =H. weeare , Wooden floors have ‘AlR SPACE : ig poares _ proved very unsatisfactory, , as they rot out in a com- Jp BOARDS ; : , ansrace ae paratively short time, due /g BOARDS Paice ce to the fact that they are Ye, BOARDS BAMPER more or less absorbent and % = . Beoanes bah ae not be readily cleaned naan pene and therefore retain odors Va e . ° Bs that may be injurious to 73 0. Ss e . - MRPAPER delicate goods. The abil- 4 HAIR QULLTS eSIT Leila ity to keep storage rooms, J scarvs especially where used for W.& PAPER ° . . isueercenx 330 storing dairy products, in ‘pecans a sanitary condition by een oe ago thoroughly washing will be %,e0arp appreciated by dairymen. When brick or concrete are used in construction the exterior of the walls should be coated with some efficient waterproof- ing compound; the walls should be thoroughly dried out, however, before the compound is applied. The customary method has been to waterproof the interior of the walls, allowimg the outside moisture to soak through the walls until it reaches the inner film of the waterproof- ing compound. IJtis much better to waterproof the outside surface of the walls, thereby preventing the moisture from penetrating through to the inner side. In cold-storage rooms the doors perhaps afford the weakest point in the insulation. While their insulation is of Fic. 23.—B. T. U. transmitted per square foot per 24 hours per degree difference in temperature. APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 57 importance, their tightness and ability to be operated quickly is vastly more so. A poor-fitting door that allows the outside air to leak into the room is a source of endless expense; consequently great care should be exercised in fitting doors in place. Usually it is economy to buy a good design of commercial door, as it will fit better and not be so liable to warp as a door built by the local carpenter. With slow and heavily moving doors which bind and work badly there is a tendency on the part of the workmen to leave them open, allowing the warm outside air to rush in and replace the cold air. Equal care Re sapere “oo: 3628 ° e Ye should be exercised in the sees B ‘ x construction of windows piesa e 2 7 in the walls of cold-stor- een nay, hw, P age rooms. They should Ig aonnvs : ay be constructed of three —- ———e Boanos. ony. plates of glass with two ESRusy eee ie ° ° syiahe . 3 fee : § B'niles en half-inch airspaces. The RNs see Seas laser fate POSNER Ste Pa glass platesshouldbecare- {8S ESE 7 soanos pame : WR PAPER 210 fully set in felt and made drawings of typical con- STRAWBOAREAINCELL FinsHED ) b'STRAWACARD 243 Tez) AT CEMENT structions of cold-storage insulations with their in- sulating values are shown in figs. 23, 24, 25, 26, and 27; they are taken from tests made by different authorities. ESTIMATING THE SIZE OF REFRIGERATING PLANTS. In determining the size of machinery for any class of work it is necessary Fig. 24.—B. T. U. transmitted per square foot per 24 hours per degree difference in temperature. % B0ARD W.P PAPER GA £c c Wh Ba meee PUITICE % CARES % BOARDS W.PPAPER IFLA FIBER % GOARDS WRPAPE. R %'soaro W.RPAPER 3"SHEET CORK 2, WAPAPER Zz 6 BOAR % BOARDS W.RPAPER 4 GRANULATED CoRK, 1.70 & BOARDS WP PAPER perfectly air-tight. The 6'PAT. SILICATED se I to carefully consider the maximum or peak load that it will be called upon to carry. This often results in having to install a great deal larger machine than would be required if the load were uniform. Inno class of machinery is this more apparent than in refrigerating apparatus when applied to the dairy industry. In figure 28 (p. 61) are curves showing the relation between the milk supply and the temperature of the air. ‘These curves are plotted from data obtained from the most important dairying States. The milk- 58 BULLETIN 98, U. S, DEPARTMENT OF AGRICULTURE. supply curve is based on the monthly percentage of the average supply. The temperature curve is the average of the mean 24-hour temperatures. Referring to the curve showing the variation in the supply of milk from month to month, it will be noted that there is practically a fixed relation between the temperature of the air and the supply of milk. The average of the milk supply, which is taken as 100 per cent, is available during April and September, while the maximum occurs during June. The highest summer temperature occurs the latter part of July and the first of August, and the maxi- mum amount of work to be done by the refrigerating plant is during July. Therefore the condi- tions existing at this time J S0ARD, 0.4m. Pb eorK. } 22S .WPPAPER DoS ie EE: SS eS ys . ‘Yacano nen ; should be taken as a basis for ZNES cont Some det eraiisiae. (ici teaae WISP ABER etermining the size of the re- 5 UZPOaros p+. | 1 ; eee | os frigerating plant required. If Zp sennn aon the capacity of the refrigerat- B BOARDS, Br = = = nes conn jee ing plant is sufficient to han- ES Poca, Dro. dle the maximum load run- =) Zsomnvs, pert Jers ning eight hours a day, it will WPPAPER ev wee Ss handle the average load run- Pie Jes ning four hours a day. The = P ~ . x 7g S0ARDS, 0.40 time of running the machine "ahnrarae 4 f : rhinceaces yee ecrease from a maximum % S0ARDS,D.tM. . . : of eight hours during July until it can be shut down entirely Yeuroserm (559 inthe Northern States during I°AIR SPACES W.R PAPER December, January, and Feb- ruary. In the South it will ‘ Jy 200rr, BoM. Z2°AIR sPacts 4 BOARDS tW.PPAPER be necessary to operate the 2170 refrigerating plant to some extent during the entire year. The curve marked ‘‘compres- sor curve”’ shows the approx- imate daily hours the compres- sor will have to be operated to produce sufficient refrigeration to take care of the milk during the different months of the year. This curve, however, is based on the milk supply and weather conditions existing in the Northern States, where the dairying industry is prin- cipally located at the present time. In the Southern States the daily hours of operation will have to be increased. However, the flush period is not so marked as in the North, as the seasons are longer; consequently the refrigerating load is more uniform and the peak load is not so great. A simple and fairly accurate estimate on the size of refrigerating machine required to do the work of a given amount of ice may be made as follows: MAIR SPACE ee we eee Ee ee % BOARDS, 0. th Fic. 25.—B. T. U. transmitted per square foot per 24 hours per degree difference in temperature. lt i TI APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 59 Suppose the ice required to cool a certain size box during the hot- test weather is 500 pounds per 24 hours. The refrigeration accom- plished by this amount of ice melting is 500 144=72,000 B. T. U. Assuming that the conditions existing in the plant will justify the operation of the ma- chine eight hours per day, then the capacity of the ma- chine must be suffi- cient to extract 72,000 B. T. U. in eight hours, or in one-third of the time that it takes to melt the ice. Therefore the capac- ity of the refriger- ating machine must 72,000 3 be 388,000 (0 745) ton. Usually lower temperatures than can be maintained by the use of ice are desired, consequent- ly a 1-ton machine, although slightly larger than the re- quirements, should be installed. In figure 29 (p. 62) are given the maximum and average tempera- tures for the different States. zB BOARS D¢t/7 WPPAPER 2’MNPS.CORK 120 VAIR SPACE % BOARDS, DNIZ WPPAPE.% ey BOARDS, 0.4. A WR PAPER INVAPS CORK qo obo 2'N.PS.CORK VAIR SPACE 7g S0AROS, DMT WRPAPER % BOARD OYM+WA PAPER ag) SS BD QRANULATED CORK TEN Ig BOARDS, 0414 tWPPAPER “ % BOARDS, 2 tM WPPAPER LAIR SPACE Vz BOAROS, 0.VK.+WR PAPER NENW REE Ws $" GRANULATED CORK 7g 2 0ARDS,D.AM.tW.P PAPER 2" AIR SPACE %g B0ARPS,0.4M, tW.A PAPER Rs A SINPS.CORK = AIR SPACE al % BOARDS. O.004.4WP PAPE 170 %g BOARD, DvP. tW.P PAPER R Fic. 26.—B. T. U. transmitted per square foot per 24 hours per degree difference in temperature. APPROXIMATE COST OF PRODUCING MECHANICAL REFRIGERATION IN SMALL PLANTS. The cost of producing a ton of refrigeration mechanically depends upon so many variables, especially in small plants, that it is impos- sible to give more than approximate costs. The average plant used in creameries and diaries is operated about eight hours daily during the summer months when the work required of the refrigeration machineryisatitsmaximum. Then the total time of operation dimin- ishes until the machine is shut down entirely or run very little during the winter months. 60 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. In most small creameries the engine is ordinarily run for only two or three hours while the churning, working the butter, and pasteuriz- ing is being done. The balance of the day the fire in the boiler is banked and only 10 to 15 pounds’ pressure is kept on the boiler. [i, ‘in order to operate a refrigerating plant, it is necessary to keep a greater pressure on the boiler and to operate an engine which is a great deal larger than is required for the compressor, the cost per ton of refrigeration will, of course, be greatly in excess of what it would be if the engine was of suit- able size for operating the : compressor only. Again, the refrigerating machines are 0-70 VA BEE 22 often operated intermit- SPs tently, thereby increasing sless wssin Semenrecasren the cost per ton of refriger- WACL CONS TAUCTION FIREPROOF P - haath ao ation above what it would i be if run continuously. In SB 200K rILe : Nf y E eae ano «View of the above, it is im- t= practical to arrive very c COUR LE ARCHES closely at the actual cost Sas per ton of refrigeration CEMENT PLASTER “FLOOR CONSTRUCTION FIREPROOF when the compressor is operated by a steam engine . which is also used for L 8 : ° Yj. driving other machinery. Sec ae ere The curves in figure 30 eet (p.63), showing the approx- Za EO4ROS, OAM. tMEPAPER = . WALL CONSTRUCTION,WOOD imate cost of producing re- S222 Poeomonnrtan frigeration in creameries Be FERAL WooL with belted, steam-driven : 7 SCARS TER EAP ER 192 } (2° CINDERS FLOOR CONSTRUCTION. Fic. 27.—B. T. U. transmitted per square foot per 24 hours per degree difference in temperature. equip ment, has been aver- aged from reports on alarge number of creameries, and in view of the fact that the engines were used for pur- poses other than driving the refrigerating machines, it should be borne in mind that the results are only approximate and should not be considered as positive. The cooling water supplied to the condenser and the wages of an attendant have not been taken into consideration in averaging the cost of producing the refrigeration. The water in most cases costs little or nothing, and it can be used for feeding the boiler, wash- ing utensils, and for other purposes after it has passed through the condenser, as it is only raised a few degrees in temperature. In op- erating small-machines of the size commonly used in milk plants, APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 61 creameries, and dairies, it is unnecessary to employ a regular attend- ant, as some persons regularly employed in other work on the premises can find time to start and stop the machine and to keep it oiled. The curve marked ‘Total cost per ton of refrigeration” has been calculated from the estimated cost of the plant, repairs, depreciation, and miscellaneous items, such as oil, waste, packing, etc. The in- terest on the money invested is figured at 6 per cent and the repairs and depreciation at 10 per cent. While the above curves representing the cost of producing refrig- eration in the smaller-sized creameries are believed to represent a fair average, it is also believed that the cost can be materially lessenedifmoreatten- 20" tion is paid to the economic operation of the compressor. In a great many in- és stances the engine drove long lines olf shafting that were not in the best of condi- tion and a number of idle pulleys in addi- tion to the refrigera- ting machine. In many instances where electricity is available motorsmay * © be installed at anad- ze 4 vantage for operating the refrigerating ma- prone chine as well as other Fig. 28.—Curves showing the relation between the milk supply and the temperature of the air, averaged from the most important gO as 1s Bg + u & rt) HOURS NECESSARY TO OPERATE COMPRESSOR. MEAN TEMPERATURE OF Alfe. a 9 9, ® A ° PER CENT VARIATION (V MILK SUPPLY 4 5 apparatus. Motors of dairying States, and the hours necessary to operate the com- comparatively slow- ‘pressor based on the maximum amount of work being done in eight hours. speed type can be readily connected by belt to the compressor. With the present price of electric power the cost of operating small units with electricity is slightly greater than when operated by steam power, provided the steam plant is run at or about normal load. But when the engine and boiler are operated at only a fraction of their capacity they become very inefficient and the cost of power is greatly increased. In view of the fact that with electricity the consumption of power starts and stops with the opening and closing of the switch it is often more economical to install electric motors for operating small refrig- 1 | | L i Sa a a en ee en oe BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. erating machines, even though the creamery is already equipped with a steam engine. This will depend, however, on the arrange- ment and efficiency of the steam plant and on the cost of electric power and must be determined in each individual case by those on the premises. The cost of power per ton of refrigeration as averaged from steam-driven plants in operation will compare with electric drive at about 3 cents per kilowatt-hour. There are other advantages in employing electric drive over steam, the value of which can not be estimated in dollars and cents, viz, cleanliness, less space required, and that the power required can be determined accurately at any time. \ ! \ \ -=-= MISS.! ALA. : Fig. 29.—Maximum and average summer temperatures in different States. Cleanliness in milk plants, creameries, and dairies is of special advantage, and with electrical drive practically all the dirt arising from smoke, coal dust, and ashes is eliminated. It is possible to install electric motors in out-of-the-way places where engines could not be located. This feature makes it practical to locate the refrigerating machine close to the cooling rooms, thereby eliminating long leads of refrigerating piping located outside the rooms to be cooled. The fact that the power required to operate the compressor can be determined accurately at any time is of great importance. This feature, however, May not seem of very great value at first thought, but it has been proved in many instances to produce higher economy. That the cost of production can be determined accurately is due to the fact that the cost of power is given in each monthly bill or, for that matter, can be calculated each day from the meter readings. With exact figures at his command the operator is able to detect APPLICATION OF REFRIGERATION TO HANDLING OF MILK. - 63 leaks occurring in production due either to careless operation or to deterioration of the apparatus and is able to judge of the exact value of every movement in the process. REQUIREMENTS OF REFRIGERATING PLANTS FOR DAIRY PURPOSES. A refrigerating plant suitable for use in milk plants, creameries, and dairies should comply with the following requirements: - (1) It should be reasonable in cost. (2) Economical to operate. (3) Reasonably sure against breakdown. (4) Should produce cool and dry air in storage room. (5) Should produce lower temperatures than ice. Bibel wn ep see Mae hs ee i ie ely EEE Mabe st cel al toll} eae ea \ \ i acane Me | MORN@ ier eka) ele | ae Reese dela lid eka [pale Pe lereeeot Le ee es TON ie 2,00 ~ 8 a Teen ME ae ooo | oo es7 e Lom Anibal Ra els eo er —_ COST PEF TON OF FPEFRIGERATIOIN Poy) ONS PoEPRIC pear Fig. 30.—Approximate cost of producing refrigeration in the average creamery with belt-driven compressors. (6) Should give perfect control of temperatures. (7) Should be simple in construction and operation as to require little attention and be successfully operated by any careful person | without any special mechanical or engineering skill. (8) Should occupy little space. The initial cost of a refrigerating plant should of course be as small as possible consistent with high-grade apparatus. It is believed that no class of machinery depends more for satisfactory | and economical operation on the original design, material of con- struction, and workmanship than refrigerating machinery. An | inferior grade of refrigerating apparatus is an expensive investment | at any price and should never be installed. With high-grade machin- 64 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. ery and properly arranged and proportioned accessories the cost of repairs and operation is reduced to a minimum. In the summer months the refrigerating plant is often required to operate continuously in order to handle the increased amount of milk during the flush season, and, furthermore, there is a greater amount of refrigeration required on account of the higher summer temperature. A breakdown at this time would result in the prob- able loss of the stored products; besides, the daily supply of milk and cream which arrives in the plant at a temperature that will cause the rapid development of bacteria if held even for a short period. Durmg the summer months the temperature of the con- densing water will be higher, and consequently a greater quantity will be required for satisfactory operation. With properly proportioned pipe coils, brine tanks or congealing tanks, and good air circulation within the cold-storage room, cool and dry air will be obtained and a lower temperature and purer atmos- phere than is possible with ice. The temperature obtained in the average refrigerator cooled with ice is seldom below 45° or 40° F., and the air always contains more moisture than it should for the best results. When employing a properly designed mechanical refrigerating plant the temperatures are under perfect control of the operator, regardless of weather conditions; consequently the result is a higher grade and more uniform product. It is absolutely necessary in manufacturing the highest grade dairy products to be able to control the temperatures at will. As the refrigerating plant is generally operated by persons unskilled in the management of machinery of this type, it should be as simple as possible in its construction and operation, especially in the smaller | plants. In the larger plants, however, where an experienced attend- ant is employed, the equipment may be more elaborate. The appa- ratus should be designed to occupy as small a space as possible con- — sistent with strength and efficiency, and as it is to be operated by unskilled persons, nothing but the very best material and workman- ship should be used in its construction. In order to keep the size of the refrigerating plant as small as pos- sible, it is advisable to provide storage tanks of ample capacity. The brine should be cooled and a large quantity held for quick action when needed, as when a supply of warm milk is received into the plant and it is necessary that it should be cooled in the shortest possible time. And, further, the cold brine in the storage room can be depended upon to hold the temperatures in case of a temporary shutdown of the refrigerating machine. In view of the fact that the quantity of milk or cream is liable to vary greatly from day to day, depending upon the supply from the APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 65 farms and upon the amount sold, it is necessary to have a consider- able margin of safety in the capacity of the brine-storage tank. The application of refrigeration for dairy purposes depends upon so many variables that it is practically impossible to treat the sub- ject other than in a very general way. Each particular case demands special study in order to obtain the best results, as there are many methods of application according to the character of the business and its particular phases. Generally speaking, however, the brine- storage or congealing-tank system seems to be the one best adapted for most plants, but the medium surrounding the evaporating coils may be either a brine solution of sufficient strength not to freeze at the ordinary working temperature, or it may be confined air, or it may be milk brought in direct contact with the cooling surface of pipes in which the refrigerant is evaporated. In many instances it may be advisable to employ a combination of the different methods in order to obtain the most satisfactory and efficient arrangement. As there are many methods of application of refrigeration to milk and milk products, we will endeavor to differentiate as far as prac- ticable between the various applications and discuss in a general way what seems to be the one best suited for the purpose, and for this reason the following classifications are made: (1) Cooling milk on the farm. (2) Maintaining temperatures during transportation. (3) Receiving stations. (4) Cooling milk in bottling plants: (a) pasteurizing plants; (0) raw-milk plants. : (5) Refrigeration in creameries, general. (6) Local creameries. (7) Centralized creameries. (8) Auxiliary creameries. (9) Cream-buying stations. (10) Market cream plants. COOLING MILK ON THE FARM. As the influence of both time and temperature combine to hasten the development of bacteria in milk, it is obvious that it should be cooled just as soon as possible after being drawn from the cow. As has been previously pointed out, the cooling of fresh milk retards the development of the bacteria, which produces fermentation in milk, thereby in turn destroying the milk by causing it to sour. The indications are that at 32° F. the development of bacteria is not only retarded, but there is apparently an actual decrease in their number when held at this temperature. The bacteria referred to, however, are those found in milk, even though produced under favor- 40083°—Bull. 98—14——5 * =e Se mia tet att 0 aS REF a 6 Eb x SOS REE ERA OOS a a en ee j gtr oe ea EE ae Se Te Ne ag ee ee ds ead I ee eee Ne 66 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. able hygienic conditions, and not to pathogenic (that is, disease- producing) bacteria. It is impracticable to reduce the temperature of milk much below 50° F. in summer without employing a refrig- erating machine or ice, and as the former is too expensive for the ordinary farmer, we are limited to the use of ice or well water. Where ice is plentiful and may be had at a nominal cost it is an easy matter to reduce the temperature to, say, 40° F., and by referring to Tables IV, V, and VI under ‘‘Influence of temperature and time on the development of bacteria in milk” it will be noted that the multiplication of bacteria at this temperature is very small. In those locations where natural ice is available it is compara- tively an easy matter to cool milk or cream on the farm before carry- ing it to the receiving station or creamery. This may be done by running the milk or cream over some form of cooler in which cracked ice or a mixture of ice and salt is placed, or through which cold water is circulated. Where the milk or cream is placed in cans and set in cool water, or even in a tank filled with ice and water, the cooling goes on very slowly, especially if the cans are large. The outside portion, how- ever, may be cooled in a comparatively short time, but unless it is stirred repeatedly it will take considerable time before the interior is cooled down to a pomt where the development of bacteria is re- tarded to such an extent that the milk or cream may be safely car- ried to the receiving station or creamery, as the case may be. It is often the case that a can of milk is set into a cooling vat in which the cooling medium is lower in level than the milk in the can, in which case the milk in the lower part of the can may be cooled down to approximately the temperature of the cooling medium, while that above the level will remain at the higher temperature of the atmos- phere; consequently, when the milk is stirred the whole will turn sour and spoil. The cold milk, being heavier than the warm, will naturally remain at the bottom of the can, while the warmer and therefore lighter portion will remain at the top, and practically no circulation will take place and the transfer of heat by conduction in this case is very slow. If proper care is exercised, however, milk and cream may be cooled down to a temperature sufficiently low to get to the receiving sta- tion or central creamery in good condition by running spring or well water through the cooler. In the winter months the lower atmos- pheric temperatures assist in the cooling, but in the hot summer months the higher temperatures of the atmosphere retard the cool- ing; consequently, during the hot weather the milk or cream should be run over the cooler very slowly, and if its temperature is not sufficiently lowered it should be run over the second time. In this APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 67 way it is possible to get the temperature down to within 2° or 4° of the cooling medium. As the development of bacteria begins as soon as the milk is drawn from the cow, it is of the utmost importance that the cooling be done as quickly as possible after milking, in order to keep the in- itial number of organisms down toa minimum. The rapidity at _ which the development of bacteria goes on in milk at a given tem- | perature depends, of course, on the initial count, hence the impor- tance of keeping the initial count as low as possible. Tests were made to determine the time required to cool milk by placing a 10-gallon can in a box and running cooling water around the can, as shown in figure 31 (p.68). The average temperature of the water was 62.6° F. and the flow of water was regulated so that there was practically no difference between the inlet and outlet water. Thermometers were placed in the can, as shown in the attached sketch, and readings were taken every 15 minutes until the tem- perature of the milk was approximately that of the cooling water. The results of these readings are plotted in the form of curves, which are numbered from 1 to 7, inclusive. Curve No. 8 is plotted from thermometer readings taken in the milk at top of can and shows that that part of the milk above the water level remains from 5° to 6° warmer than the portion below the water level; consequently, bacteria will develop at a higher rate in that portion of the milk above the water level and when mixed will hasten the souring of the milk, both by raising the temperature of the whole and by the in- creased number of bacteria contained in the warmer portion. The curve showing the comparatively rapid decrease in tempera- ture when the milk was thoroughly stirred at intervals of 15 minutes demonstrates the advantage of agitating the milk while cooling. The time taken to cool the milk in either case, however, is too great for good results, and the tests serve best to demonstrate the necessity of employing some efficient form of milk cooler suitable for farm use. Figure 32 (p. 69) shows the method of cooling milk employed on the United States experimental dairy farm located at Beltsville, Md. The equipment consists of a one-fifth ton refrigerating machine operated by a one-half horsepower motor, a small rotary circulating pump driven from the shaft of the refrigerating machine, and a corru- gated milk cooler. Water, instead of brine, is used for circulating | through the cooler as the night’s milk is cooled, placed in cans, and | set into the tank until the next morning; if brine were used [it would corrode the cans. The tank holds about 120 gallons of water, which is cooled down to approximately 35° F. and held at this tem- perature until time for cooling the milk, when it is pumped through see NM Gee > Lies piel I TD BO eA tm = 4 san / mew . -_ a 68 ), y y 4 17 y y) y th a 1 A 2 c fA 7221 6758°F 62.6°F OL RQE CURVES (TOT PLOTTED FROM CORRESPONPING Room Room CURVE NO.B PAOTTED FROM THERMOMETER ARRANGEIMENT FOR TEST. THILM STIFFREO EVERY IS MINUTES:- READING TAHENIN TOP OF CAN, AVERAGE TEMP COOLING WATER 62.5 he oo MULK NOT STIRRED.- AVERAGE TEMP COOLING WATER a o Ese Bs Be eM SCV CCC ACA aE 8 04 SBN GRE REO ZY) COCNSSE EEA ‘TEMPERATURE DEGREES F: MILK NOT STIRRED. hal cl Fitba 2 fendi baseeailaie) dale naling Raa Seg TEMPERATURE DEGREES F MILK STIRRED EVERY IS PUNUTES- = . Raa. . 6 330 00 230 20 £30 4 oe. BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. Fie. 31.—Cooling milk with running water. foal He APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 69 the cooler by the small rotary pump. The water is allowed to pour back into the tank, consequently the temperature of the volume of water gradually rises. During the warmest weather it was necessary to run the refrigerating machine from 8 to 10 hours a day in order to cool the water down to 35° F. and hold it at this temperature until used. The volume of milk handled was that from 15 cows and it was cooled entirely by the refrigerating water from a temperature of about 98° to 35° F. Had well water been used in one section of the cooler at least half of the refrigerating duty would have been taken off the machine and the time of operating the machine would have been reduced one half, or, for the same number of hours of operation the SECTION THROUGH REFRIGERATING Bch PIACHINE AND COLD WATER TANK, © CAN RACK. _ a1 i ES lh =e, ioe = 1 ue ad ke = i = Sing a b | r re se i es “i VEEN HG |e H eet Fig. 32.—20-cow farm milk house equipped with refrigerating machine. machine would have taken care of the milk of double the number of cows. The cost of electric current at the experimental farm is 6 cents per kilowatt-hour, and as the input to the motor is about 0.55 horse- power, the cost of power for operating the machine 1s 23 cents per hour, or 20 cents for an 8-hour day. The amount of cooling water required is about 25 gallons an hour. MAINTAINING LOW TEMPERATURES DURING TRANSPORTATION. A great deal of the milk consumed in the cities at the present time is transported in wagons, or in the ordinary baggage car in use on the steam railroads or on the interurban electric railways, with no provi- sion for holding the milk at low temperatures. 70 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. | If, however, milk is thoroughly cooled on the farm and placed in large cans properly jacketed it will arrive at the city plant in good condition under ordinary weather conditions providing the time required for transportation is not over four hours. The transfer of heat through milk is principally by convection, and when in large volumes the transfer is very slow unless the milk is agitated. The time taken in the transportation of milk from one point to another, together with the facilities available for holding it at low temperatures, determine, to a great extent, the initial temperature to which it should be cooled. For short distances, or short preserva- tion of a few hours only, it is believed that a temperature of less than 50° F. should be maintained. Some lactic acid bacteria will multiply even at this temperature and will cause a souring of the milk, but the increase is slow and for a few hours no serious results will occur. At temperatures below 50° F., however, the rate of bacterial growth is materially decreased. If, on the other hand, milk is to be shipped long distances, the initial temperature must be lower, assuming that no provision is made for maintaining temperatures during transportation. For com- paratively long-distance shipments, where the milk is in transit for several hours, it is necessary to cool it down near the freezing point. The point to which milk should be cooled, therefore, depends on the time taken in transportation and must be determined for each par- ticular case. In order to maintain a low temperature as long as possible, the cans should be well jacketed. The curvesin figure 33 (p. 71) show the result of jacketing the cans. The cans were set in an open truck with no covering to shield them from the direct rays of the sun. Long- stemmed thermometers were inserted through holes drilled in the covers of the cans. Thermometer readings were taken every 15 minutes and the results plotted in the form of curves. The milk was hauled a distance of 13 miles through the country and the average air temperature during the trip was 82.65°. It will be noted by refer- ring to the curves that the total rise in temperature of the milk con- tained in the hair-quilt-jacketed can was 5$°, while that in the can wrapped in wet burlap was about 84°, and the unjacketed can showed a rise in temperature of 284°. It is obvious from the curves that it pays to jacket the cans in order to maintain a low temperature during transportation. There are at the present time two types of refrigerator cars de- signed especially for the transportation of milk. One is an ordi- narily constructed car of the baggage type, in which the milk cans are set and crushed ice packed around them. ‘These cars are only good for comparatively short hauls, as they are poorly insulated or in most cases not insulated at all. The water from the melted ice APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 71 is allowed to run out at the doors, or through cracks in the floors. The other type of car is provided with ice bunkers or brine tanks. In these cars the bunkers are located in the ends of the car and haye a ratio of ice to loading capacity of about 1 to 11 cubic feet. In some of the more recent designs of milk cars a mixture of salt and a le) eo | le es pes ele] 7 De [ene as ae maa oes [vale] esis fife] fn] Sole [ faa Hv ah ole a aa | Ee ee _ PES mn ee ar me et lb el a A 4 DEGREES RISE IN TEMIPRATURE | cca + Pen Se Se eee PA eal sess lee TIME — PUNUTES. Fig. 33.—Curves showing the relative rise in temperature of milk contained in insulated and uninsu- lated cans. Average air temperature, 82.65° F. ice is used to obtain lower temperatures than can be had with ice alone. One of the latest designs of refrigerator cars for use in trans- porting milk, employing a mixture of brine and ice, is constructed with two refrigerator compartments, each having a floor capacity of 160 46-quart cans, 13 inches in diameter. The volume of the refrigerating compartment is 1,468 cubic feet. The design of brine 72 BULLETIN 98, U. S$, DEPARTMENT OF AGRICULTURE tanks consists of two tanks having a radiating surface of 226 square feet and a volume of 77.25 cubic feet. The screened portion above the tanks has a volume of 9.42 cubic feet, making a total capacity of 86.67 cubic feet, or a total of 3,814 pounds crushed ice, weighing 44 pounds per cubic foot. The ratio of tank radiating surface to loading volume is 1 square foot to 7.48 cubic feet, and the ratio of ice to milk is 2 pounds of ice to 1 gallon of milk. The tanks have a 2-inch free-air space around them and are 15 inches above the floor. They are separated from the storage rooms by a partition open at top and bottom and screened, thus creating a circulation. Any moisture from tanks is carried off from drip pan through drain pipes and traps. The tanks are connected by 14-inch pipe, creating to some extent a circulation. This pipe also regulates the brine to a uniform height in both tanks, the height of the pipe above the bottom of the tank being so arranged that a certain amount of brine remains. A riser connection to the pipe forms an overflow. When refilling the tanks, the valve in the pipe connecting the tanks is opened and all water or brine above the horizontal pipe is drained off. Before refilling the tanks with crushed ice and salt the valve is again closed, causing the warm water to rise to a height equal to the top of the pipe. Any surplus water runs off through overflow pipe and outside trap without egress of air. The valve is manipulated by a rod and universal joints from the roof of the car by removing the plug door. When it is necessary to clean the tanks, the round plugs at the bot- tom are unscrewed about one-fourth inch, when they will release the brine, and after it has drained off the plug can be entirely unscrewed and the settlings removed. In order that the car can be kept in a sanitary condition the floor is covered with galvanized sheet iron, all crevices being soldered, and after each trip or shipment of milk the floors are scrubbed. It is practicable with this type of car to maintain a temperature of about 35° or 40° F. The milk must be precooled, however, to about this temperature before it is placed in the car, as the refrigerat- ing apparatus is not intended to receive warm milk from the shipper and reduce its temperature to any great extent during transit. A longitudinal section of this car is shown in figure 34 (p. 73). COOLING MILK AT RECEIVING STATIONS. Receiving stations as applied to the milk industry are established for the purpose of receiving, cooling, and handling milk preparatory to shipping. They are located at suitable points along the railroads in dairy sections. The milkis brought to the receiving station by the farmers, usually twice a day during the summer months, early in the —— APPLICATION OF REFRIGERATION TO HANDLING OF MILK. (8 morning and again in the evening. During the winter months the farmers often hold over the evening’s milk until the following morning, mak- ing only one delivery a day. This is especially true when the farm is located at some distance from the receiving sta- tion. During warm weather, however, one delivery a day is impracticable, un- less some method is provided on the farm for holding the milk at a tempera- ture sufficiently low to prevent the rapid development of bacteria. It is necessary that the receiving sta- tions be provided with some means of cold storage in which to store overnight the milk which is received in the even- ing, and to guard against delays in rail- road service, etc. Most of the receiving stations are owned and operated by the city milk dealers. A few, however, are coopera- tive or have independent owners. The equipment of these stations varies sreatly. The equipment of the smaller stations usually consists of a water tank for ice water and cans, with a small boiler _ to produce hot water or steam for wash- ing cans and other utensils. The more elaborate establishments are equipped with pasteurizers, bottling machinery, bottle washer, separator, churn, cream vats, and an ice crusher or a refrigerating machine. The latter type of stations are equipped with the view of regulat- ing as far as possible the surplus milk received during the flush season at the station instead of in the city by making butter, condensing, or by separating and shipping only the cream. Assoon as the milk is received it is Im- mediately sampled, weighed, and cooled and either bottled or placed in cans ready for placing on board the cars. In the smaller stations the cooling is ac- complished by setting the cans into a tank containing ice water, but in the more elaborate establishments = —————— ab " _ te Se eer ase ae 7 HH Bu ae, Sree SS es Fie. 34.—Modern refrigerator car. ol 74. BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE, as soon as the milk is received it is weighed and dumped into a vat from which it runs over the cooler to the bottling machine or into cans. Ice water or brine, or often a combination of the two, is cir- culated through the pipes of the cooler; ice water being run through the upper tubes and brine through the lower. The principal work, therefore, of the receiving station is that of cooling and preparing the milk for shipment. The lower the temperature of the milk, so long as it is kept above the freezing point, the better. With the present state of development of refrigerator cars used in the trans- portation of milk, they can not be depended upon for lowering the temperature to any great extent during transit; consequently the milk should be thoroughly cooled before loading on the cars. Usually several hours elapse between the time the milk is drawn from the cow until it is loaded on board the cars, which makes it imperative that it be precooled. The cooling takes placed early in the morning and late in the afternoon, as the milk is received. The time required for cooling seldom exceeds two hours for each period, making the total time employed in cooling about four hours daily. Owing to the short time in which the cooling is done the capacity of the refrigerating apparatus is necessarily large for the amount of work required. It is possible, however, to decrease the capacity of the plant by running the machine a longer time and storing refrigeration in brine, which can be held for quick action when needed. COOLING MILK IN BOTTLING PLANTS. Milk-bottling plants are usually located in cities or towns. The milk is generally shipped in cans direct from the farms or receiving stations, arriving at the bottling plants at a temperature of approxi- mately 60° F. As soon as the milk is received at the city plant it is cooled to a temperature of 45° or 50° F., bottled, and placed in a refrigerated room, and held until the followimg morning, when it is delivered to the consumer. As the temperature of the room is around 32° F., the milk will come out in the morning at 35° or 40° F. PASTEURIZING PLANTS. In those plants where the milk is pasteurized previous to cooling the refrigeration required is, of course, considerably greater than in raw-milk plants, where the temperature of the incoming milk is simply reduced to 35° or 40° F. The amount of refrigeration required, however, depends upon the pasteurizing equipment employed. There are in use at the present time two systems of pasteurization, known as the “‘holder” and ‘‘ flash” processes. The holder process consists in holding the milk or cream for about 30 minutes after it has been heated to the pasteurizing temperature of 140° to 150° F., either in the same apparatus in which the pasteur- APPLICATION OF BEFRIGERATION TO HANDLING OF MILK. 75 ization takes place or in separate holding tanks arranged for the pur- pose, after which it flows to the coolers. In the ‘flash,’ or continuous, process the milk flows from the receiving tank to the pasteurizer, where it is heated to a temperature of from 160° to 165° F. in from 30 seconds to a minute, and from thence to the coolers, where it is cooled. It is obvious, therefore, that there is more refrigeration required for a given amount of milk or cream in the latter, or ‘‘flash,” than in the former, or “holder,” process. It is advisable, however, in both the ‘‘flash”’ and “holder” processes of pasteurization to install be- tween the heater and the cooler a regenerator or heat exchanger, in which the heat is transferred from the hot milk leaving the heater to the cold incoming milk; consequently the milk entering the heater is thus heated while that entering the cooler is partly cooled, the cooler proper reducing the temperature to the point desired. The milk coming from the regenerator enters the cooler at an average temperature of about 88° F. and is reduced by the water section of the cooler to about 75° F. It then enters the brine section of the cooler, where the temperature of the milk is lowered to an average of 45° F. by low-temperature brine circulated through the coils of the cooler, or in some cases by direct expansion of the refriger- ant in the coils. The cooled milk then flows from the cooler to the bottler, where it is bottled and capped, after which it is stored ina refrigerated room and allowed to remain overnight. As the tempera- ture of the storage room is around 32° F. the milk is further reduced to approximately 35° F., at which it goes on the wagons the following morning and is delivered to the consumer. The work required of the refrigerating machine in a plant of this kind is that necessary to reduce the temperature of the milk from about 75° F., the temperature at which it leaves the water section of the cooler, to, say, 45° F., the temperature at which it leaves the brine section of the cooler, and that necessary for further cooling the milk after it is placed in the cold storage room; also that required to take care of the heat that comes through the insulated walls of the storage room and in lowering the temperature of the glassware and bottle cases. The heat that will come through the walls of the room, of course, depends upon the size of the room, the quantity and quality of the insulation used, and upon the temperature of the outside air. Assuming a plant handling 1,000 gallons of milk daily, the size of the storage room necessary will be approximately 12 by 13 by - 12 feet, with an anteroom, say 6 by 12 feet, giving a total square foot surface of 1,316. If the walls, floor, and ceiling are msulated for a heat transmission of 2 B. T. U. per square foot per 24 hours, for each degree difference between the inside and outside tempera- tures, and if the average outside temperature is 80° F., then the > eer - “ee, © “an “ER == 2 = ee 76 BULLETIN 98, U. S, DEPARTMENT OF AGRICULTURE. refrigeration necessary in 24 hours, when the plant is operated under the foregoing conditions, is: Bia Ui. Removing heat coming through walls, floor, and ceiling, 1,316 & 2 (80-32)= 126,326 Cooling 1,000 gallons of milk, 1,000 X 8.6 + .95 (75-32)= 351, 310 477, 646 Additional refrigeration is also required for cooling the glassware and boxes, also a considerable amount is lost due to opening doors and the presence of lights and workmen inside the room. As it is impossible to calculate the refrigeration lost in opening doors, it is customary in practice to allow about 50 per cent additional to cover this. Therefore, the total refrigeration required in 24 hours is, 477,646 X 1.50 = 716,469 B. T. U. 0755000 refrigerating machine in a plant of this size is operated only about 8 hours during the 24, the capacity of the machine will have to be three times as large, or 74 tons. The operation of pasteurizing, cooling the milk to approximately 45° F., and bottling and storing takes about two hours; conse- quently it is necessary to have a large volume of cold brine available for this work. The cooling of the brine is accomplished during the forenoon, before the milk arrives, and as the temperature of the brine rises during the cooling process, it is again cooled down in the afternoon and depended upon to hold over temperatures in the storage room during the night. As a cubic foot of calcium-chlorid brine will absorb about 52 B. T. U. for each degree rise in temperature, and allowing a 15 degree rise, 30 to 45 degrees, each cubic foot will take up 52 (30-45) = 780 B. T. U. The volume of brine necessary for cooling the milk will be =2itons. Butasthe 351,310 _ 1805 Te 450 cubic feet, providing the refrigerating machine is not operated at the time, but as a 74-ton machine is capable of extracting 12,000 x 7.5=90,000 B. T. U. an hour, or during the two hours taken to cool the milk the machine will extract 90,000x2=180,000 B. T. U., consequently the actual cubic feet of brine required is oo Saisie — SES = 219.6. Another method of calculating the amount of brine storage required to cool a given amount of milk, based on the capacity of the com- pressor used for cooling milk, is as follows: p— (WRm)— (12,000 CHm) 60 Rb Where 7’=cubic feet of brine in tank. W =weighing of milk in pounds. ——— APPLICATION OF REFRIGERATION TO HANDLING OF MILK. Al Rm =temperature range of milk. ('=capacity of compressor used for cooling milk. Hm =hours required for cooling milk. &b=temperature range of brine. Taking the values in the case under consideration and substituting in the above formula and solving for the number of cubic feet of brine, we have: 43) — : Te (8,600 x 43) — (12,000 x 7.5 x 2) BH Me 60X15 During the 16-hour shutdown period the heat that will come through the walls, floor, and ceiling will be see = 842A B. T. U., then 219.6 cubic feet of brine will absorb in rising 1 degree 219.6 X52 = 11,419 B. T. U., or the temperature of the brine will rise during the 16-hour shutdown period, disregarding the milk in 84,224 11,419 _ A cubic foot of milk in rising 1 degree will absorb about 61 B. T. U. Therefore the milk in storage, disregarding the brine, would rise onty 84224 : 8,052 Considering both the brine and milk, a cubic foot will absorb 132 X61 + 219.6 X 52 132 + 219.6 84,224 ° 351.6 X55.4 Had the refrigerating machine been of sufficient capacity to have cooled the milk through the required range of temperature in the two hours it took to pasteurize, the size of the machine necessary 351,310 x 24 2X 288,000 would, therefore, be idle most of the time, and as the initial cost of the larger machine and equipment would be a great deal more than the smaller one, it would be poor economy to install the larger machine. When either the ‘‘flash”’ or ‘‘holder’”’ process of pasteurization is employed, the temperature of the milk is generally first lowered to approximately 75°F. by water from the city mains or from wells; con- sequently the refrigerating machine has only to lower the tempera- ture of the milk from the temperature at which it leaves the water section of the cooler to the temperature attained in the storage room. storage = 7.4 degrees. = 10.5 degrees. =55.4 B.T.U., and the rise in temperature will b =4.3 degrees during the 16-hour shutdown period. would have been =—14.6 tons. A machine of this size RAW-MILK PLANTS. In raw-milk plants it is only necessary to cool the milk from the temperature at which it is received, say 60° F., to a final tempera- ture of approximately 32°F. It is usually pumped directly from the 78 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. receiving tank through some form of cooler to the bottler, where it arrives at about 45° F., after which it goes to the storage room. The refrigeration in the storage room is obviously the same as in the pasteurizing plants. The refrigeration necessary to reduce the temperature of the milk from 60° to 32° F. is 1,000X8.6x0.95 (60—32) =228,760 B. T. U. The heat coming through the floors, walls, and ceiling is the same as before. Therefore the total amount of refrigeration required in 24 hours, allowing 50 per cent for opening doors, presence of workman, 532,644 288,000 eight hours the size of the machine required is 1.85 x 3=5.55 tons. The volume of brine required to cool the 1,000 gallons of milk with 760 — 133.2 oe cubic feet. The heat poor workmanship, etc., is =1.85 tons, or to do the work in machine running Is 126,336 X16 = 84,224 B. T. U. The rise in temperature of brine and milk will be Sa tee | 254.5X56.7 peer In figure 35 (p. 79) are shown curves of the approximate size and cost of belt-driven refrigerating equipment for various sized milk plants. that will come through the walls, floor, and ceiling is REFRIGERATION IN CREAMERIES. GENERAL. In the application of mechanical refrigeration to creameries the first method employed “or cooling cream was to allow it to run over a cream cooler on the way from the separator to the cream vat. This method allowed the cream to be exposed to the air and its con- taminating influences; besides, there was no way provided for hold- ing the cream at a constant temperature after 1t had reached the vat. The next step was to place the brine piping in an open cream vat. This caused unequal temperatures in the cream and prevented the ripening process from going on at a uniform rate, as that portion of the cream in close proximity to the cooling pipes was chilled down considerably below that at some distance from the pipes. The cream was still exposed to the atmosphere, however. Consequently this method was finally discarded. Then followed the method of locating the brine or ammonia piping in the water space surrounding the vat, but with this arrangement, as in the foregoing, it was necessary to stir the cream occasionally in order to equalize the temperature of the mass. This method was an improvement, however, as the piping submerged in the jacket water became coated with ice and after the circulation of brine or ammonia had been discontinued the ice would melt and maintain a APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 79 fairly low temperature until the cream was ready to churn. This method also had the additional advantage of allowing the brine to be circulated through the coils in the lining of the cream vat after the plant proper had been shut down. The latest ripening apparatus is arranged for brine circulation through a spiral immersed in the cream and which is rotated at a constant speed, thereby maintaining a constant temperature. By varying the flow of brine any desired temperature may be obtained. The vats are closed and insulated. Consequently contamination ss : - Qo Ney rx ut | | CARE Oe eee DOR Sooo Cocca ae rae acc Pleat (ld (aa mene tr co eee ee eee ere CEC ere eee ere steals ral a AS TeMBMMGRo ORL eee ke PESM@EEc LT Lhe 8 aE ea rey ea een Gee ee cee eae 8 cd | | RUC ee a ae <5 a a REG rmssic ee el oT ae A ea Ss OP see SA — pA" C2 a Bere | TONS REFRIGERATING GAPACITY OF PLANT. Fig. 35.—Curves showing the approximate size and cost of belt-driven refrigerating equipment for various size milk plants. from the surrounding atmosphere and changein the temperature of the cream are prevented. In no business is temperature control of more importance than in the handling of milk and its products. The perishable nature of milk and the rapidity with which it deteriorates when exposed to ordinary temperatures make thorough cooling facilities a necessity. In the production of the highest grade of butter it 1s absolutely necessary that the temperature of the cream during the ripening process be under perfect control in order to check any further fer- mentation when the proper degree of acidity is reached. As the control of temperatures is very important in the manufacture of high-grade butter, it can best be accomplished by means of mechani- cal refrigeration, as it enables the buttermaker to control the tempera- 80 _ BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. tures of the cream at will, and furthermore mechanical refrigeration does away almost entirely with the mold and slop that must neces- sarily follow the use of ice. A creamery equipped with a mechanical refrigerating plant can at all times, provided the cream is of good quality, turn out a uniform grade of butter, regardless of weather and temperature changes. In the modern creamery refrigeration is employed in connection with the processes of pasteurizing, ripening, churning, in the prepa- ration of starters, cooling water for washing butter, in cooling storage for the finished products, and frequently the raw products. In the pasteurization of cream the same methods are employed as In the pasteurization of milk, viz, the “flash”? and “‘holder” processes. In the “flash’’ or continuous process of pasteurization the cream is heated to a temperature of 160° F. in about 30 seconds and is then run over some form of cooler where the temperature is lowered to about 65°. From the cooler it is run into the ripening vats, where the proper temperature is maintained for 18 to 20 hours, at which time the cream has ripened sufficiently for churning. As a temperature of 65° is entirely too high for churning, it is lowered by running cold water or brine through the coils in the vat or through the coils of the cooler, should a cooler be used, and the temperature lowered to that necessary for churning. In practice, however, the ripening temperature of cream varies within wide limits. A ripening temperature that will give good results under certain given conditions would, perhaps, give poor results under different conditions. Consequently the existing con- ditions will to a great extent govern the ripening temperatures. When the cream is ripened, cooled, and churned on the same day, a higher ripening temperature is of course necessary, while, on the other hand, if the cream is ripened overnight, a comparatively low temperature is employed. The range of ripening temperatures varies from 60° to 80°, but it is beheved that between 60° and 70°, with an average of 65°, the best results are obtained, as cream held at these temperatures does not ripen very rapidly. Consequently the desired degree of ripening is approached very slowly and the fermentation may be checked quickly when the desired degree of acidity is reached, thereby reducing to a minimum the chances of getting overripe cream. If, however, the cream is ripened at a high temperature there is a great danger of getting overripe cream. During the ripening process extreme and rapid changes of tempera- ture in the cream should be avoided as muchas possible, as the more uniform the temperatures are kept the better the results. It is believed that the tendency is toward the ‘‘holder”’ process of pasteurization for cream and also toward pasteurizing directly in the ripening vats. Some types of modern ripening vats are provided with spiral coils or disks through which low-temperature water or APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 81 brine is circulated, and the temperature is controlled by regulating the flow. The coils are rotated at a constant speed, thereby insuring even temperature throughout the mass of cream. With an arrange- ment of this kind the temperature of the cream is raised to 140° and allowed to stand for 30 minutes, when it is cooled quickly to about 65° by circulating cold water through the coils. The cream is allowed to stand at this temperature until it is ripened. The temperature must again be reduced to 52° to 60° before the ripened cream is run into the churn. This latter reduction of temperature of about 10° is accomplished by low-temperature brine or ice water. The proper churning temperatures also vary, but in summer from 52° to 54° is considered to be an average, while in the winter, the churning temperature rises to about 56° to 60°. 3 The term ‘‘starter’’ is used to designate a quantity of milk in which lactic acid-forming bacteria have been cultivated until it contains large quantities. This starter is added and seeds the cream with great numbers of these cultivated bacteria, which by their growth cause the acid formation to progress rapidly and in a more definite manner than without the addition of the starter. In the preparation of the starter a quantity of good skimmed milk is taken and heated to a temperature of 185° to 190° and allowed to stand for 30 minutes, after which it is cooled down to 70° or 80°. To this milk is added the mother starter, which is a pure culture of the desired bacteria, in sufficient quantity to sour the skimmed milk in about the desired time. In order to develop the proper flavor, the perfect control of the temperature of the starter milk is necessary. Where the starter is made every other day it is pre- served by holding at a temperature of 50° or below. The amount of starter usually required is one gallon for every 10 or 15 gallons of cream. ‘The cooling of the starter from the pasteurizing temperature, 185° to 190°, is usually done by circulating well water through the jacketed space surrounding the starter can; consequently, mechanical refrigeration is only required to preserve the starter in storage. An ample supply of pure cold water for working the butter is very desirable. The average temperature of well water, especially in the South, is too high for washing butter; consequently it becomes necessary to cool the water to a temperature sufficiently low for this work. The temperature of the water used in washing the butter depends to a certain extent upon the character of the butter. In summer weather, wash water at a temperature of about 52° to 56° is considered satisfactory, while in winter, the temperature may be as high as 60° to 62°. It may be generally stated that the tempera- ture of wash water should not vary more than from one to three degrees below the temperature of the buttermilk. : 40083°—Bull. 98—14—_6 82 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. The cooling of wash water is done in tanks which should be located at an elevation sufficiently great to command the butter worker and churn. The cooling is done either by direct expansion or brine coils submerged in the tank. The capacity of the tank necessary will vary with the size of creamery, but tanks holding from 100 to 500 gallons are of sufficient capacity for the majority of creameries. In the medium and smaller sized creameries a cold storage is pro- vided of sufficient capacity to hold at least a week’s output of butter, as it is not always convenient to make shipment as soon as made. ~ The question of the proper temperature at which butter should be stored is an open one. It is at its best, however, when freshly made, and its fine quality will last only a few days if kept at the ordinary summer temperatures. Experiments show that the changes which take place in butter and cause rancidity and other disagreeable flavors diminish as its temperature is reduced. Consequently its quality is determined by the temperature at which it is held rather than the time. The quality and flavor of butter will eventually deteriorate under any storage temperature that has so far been tried. There- fore, the effect of stormg at different temperatures is only a matter of degree and not of absolute stoppage of all changes. It is believed that in the individual creamery where not over a week’s output is in storage at one time, that a temperature of 32° F. is satisfactory where mechanical refrigeration is available. Where refrigeration is accomplished by using ice, it is impracticable to get so low a temperature, 50° to 45° F. bemg about the temperature main- tained in the best ice refrigerators. LOCAL CREAMERIES. Local creameries are either cooperative or privately owned, and receive milk or cream, or both, from the immediate vicinity or from their auxiliary creameries located near by. Their equipment usually consists of pasteurizers, coolers, churns, etc., with the necessary motive power apparatus, and often separators for handling the whole milk, which may be delivered direct to the creamery instead of to the auxiliary creamery. Often the local creamery is not supplied by auxiliary creameries but depends on the farmers of the immediate vicinity who deliver the whole milk directly to the creamery, in which case the local creamery does all the separating. Probably the majority of local creameries are supplied with cream separated on the farm and delivered by the patrons to the creamery, or col- lected by cream haulers. In a local creamery making, say, 2,000 pounds of butter daily the method of operation is as follows: In the morning the cream which has been allowed to stand and ripen overnight in the ripening vats is emptied into the churns and the churns started. About three-quarters of an hour is required a Ss = > APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 83 to do the actual churning, and about 20 minutes more to work the butter. During this time the cream ripeners are washed. The arriving cream from the auxiliary creameries or farms is weighed, sampled, and pasteurized. The pasteurizing may be done either in the ripening vats or in a separate pasteurizing machine. When the cream is pasteurized in the ripening vats it is cooled by running cold water through the coils and the jacket surrounding the vat. When a separate machine is used, the cream is run over a cooler on its way to the ripening vats, where it is held at the proper temperature for ripening from 18 to 20 hours. After the churning is finished and the butter packed in tubs or boxes and stored in the refrigerator, the churns and other apparatus are washed as well as the floors of the building. The afternoons are usually given up’ to office work, making repairs, etc. The machinery is, therefore, operated only about eight hours a day; consequently, the refrigerating machine should be of sufficient capacity to do the work in about eight hours’ time. The size of the room necessary to accommodate a creamery making 2,000 pounds of butter daily is about 10 by 10 by 10 feet, giving 600 square feet surface. Assuming that the walls, floors, and ceiling are insulated for a heat transmission of 2 B. T. U. per square foot per 24 hours for each degree of difference between the inside and outside temperature, then with an average outside temperature of 80° F. the refrigeration necessary is: BavlenUe Removing heat coming through walls, floors, and ceiling, 600 2(80°-82°)... 57, 600 Goolimeatencamynn 000) 90(10°—00" )e. 2. --- ae oe ee aes 123, 750 Caolimeatauiten 2 )000)<9494(58°—320) 26-22 hoe ase ole ee 28, 568 209, 918 In view of the fact that the greater part of the refrigeration is required for cooling the cream, an increase of 25 per cent to com- pensate for losses of various kinds should be ample. Therefore, the total amount of refrigeration necessary in 24 hours is 262,398 B. T. U. But as the work is to be accomplished in 8 hours, the capacity of the 262,398 X 3 288,000 The cooling of the cream will take about one hour and the amount of brine necessary, allowing a 10° rise in brine temperature, is 123,750 520 With the machine running during the time the cooling takes place, 123,750 — 36,000 Toa Ragr =168. After the cream is cooled and run into the vats for ripening, the brine is cooled down for holding over the room temperature during the machine necessary is: =2.73 tons, say, 3-ton machine. —238 cubic feet, without the aid of the machine at the time. the cubic feet of brine necessary is 84 BULLETIN 98, U. S, DEPARTMENT OF AGRICULTURE. night. The heat that will come through the walls, floor, and ceiling 57,600 x 16 during the shutdown period is ie pa B. T. U. and the RE ST Ue tig Tay eee temperature of the brine will rise 168X592 4.4°, The curves in figure 36 show the approximate size and cost of belt- driven refrigerating plants for various sized creameries. The curves are estimates under average conditions of operation and were checked by a large number of such plants now in operation. In the construction of the cold-storage room great care should be exercised in selecting and installing the insulation. It has been shown under the section on insulation that three-fourths of the work Pitect Se ara Ce is) Le | eel Sel |e lela lea FERENCE EEE eS SL || SAS De ae i ee Fic. 36.—Curves showing the approximate size and cost of belt-driven compressors for various size creameries. Q SERRE ERREERCOBESeR Coe ESN RE ER REESE meee oo JOS SCARS RRB mmm oe alba Sell dl 4 lose Jeti lial yoda Seek lol ad oll Li = i (SEGGGR “Bbc UseeBBE bus. JOBS SR Ge QE Ewen L < S OCCA ee See Par ee si se 2 alba nner = Saal ela of refrigeration required for cold storage is utilized in ‘‘pumping out,’ so to speak, the heat that comes through the walls, floor, and ceiling of the room. In addition to the insulating value of modern insulation, it serves as a protection to the goods in storage in case of fire, due to its slow burning qualities. It is often advantageous in creamery cold storage to provide extra rooms for the purpose of storing eggs and poultry. They should never, however, be stored in the same compartment with the dairy products, as they will impart a taint to these goods. CENTRALIZED CREAMERIES. Centralized creameries, as the name implies, are established for the purpose of handling and manufacturing into butter the cream received from many outlying stations, or from direct shippers. The outlying stations are usually termed ‘‘cream-buying stations” and often located at a distance of 100 miles or more from the main creamery. APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 85 The centralized, or main, creamery is usually located on a rail- road or, better still, at the intersection of two or more railroads. The cream-buying stations are distributed along the lines of the railroads in the most favorable locations for collecting cream. The collected cream is shipped to the centralized creamery, the time of arrival, of course, depending upon train schedules. In some instances cream arrives at practically all hours, both day and night. As soon as_ received at the creamery, the cream is sampled, weighed, and pas- teurized. After pasteurization the cream is cooled and run into vats where it is held until the following morning, when it is churned. Generally the churning and the working of the butter take place in the forenoon, although in some instances this work is done at any time that happens to be the most convenient. : Usually the cream is ripe when received, and if churning is to be delayed the temperature of the cream is lowered to a point where the development of acid bacteria practically stops, at which tempera- ture it is held until ready to churn. In case a force is kept on duty continuously, the refrigerating plant may be operated 24 hours a day; hence, the size of the plant is ma- terially reduced from that required if the plant were operated only 8 hours. Generally speaking the methods of operation employed in the centralized creameries are very similar to those of the local creamery, except they are on a more extensive scale and only cream is handled. CREAM-BUYING STATIONS. Cream-buying stations are established for the purpose of supplying the centraJized creameries with cream by collecting the cream directly from the farmers and shipping to the main creamery. These stations are located at suitable points along the railroads in close proximity to a large number of farms. The cream is brought to the buying stations by the farmers, where it is received by the agent of the main creamery and held until a sufficient quantity is on hand to justify shipping. Generally no provision is made for cooling the cream at the buying stations. In figure 37 are given the weights of a gallon of cream containing varying percentages of fat. COOLING CREAM IN AUXILIARY CREAMERIES. The auxiliary creameries, commonly known as skimming stations, are erected for the purpose of furnishing cream to the main creamery without the inconvenience of having to haul the raw milk a long dis- tance. By separating the cream from the milk in the auxiliary cream- ery and hauling only the cream to the maim creamery a great saving in time and labor is effected, as it is necessary to haul only about an average of 13 per cent of the total weight of the whole milk. 86 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. The auxiliary creameries are located at suitable poimts in the country surrounding the main creamery, where they are in close proximity to a number of farms. Where a creamery draws its sup- ply of milk from a large and scattered area, the auxiliary creameries are essential to its economical operation. The milk is brought to the auxiliary creamery by the farmers early in the morning and it is immediately sampled, weighed, and sepa- rated. The skimmed milk is returned to the farmers, who haul it home for feeding to stock, and the cream is run from the separator over a cooler, caught in cans, and carried to the main creamery, where it is ripened and made into butter. In some States the skimmed milk is heated before being delivered to the farmers to a temperature of 180° F. in order to destroy any disease-bearing bacteria that might be transmitted to stock by feeding on the milk. PER CENT FAT: WEIGHT IY POUNDS FER GALLON OF CREA. Fic. 37.—Weight of a gallon of cream at 68° F. with varying percentages of fat. Before separating the whole milk its temperature is raised to 90°. It is then run through the separator, coming out at a slightly lower temperature than that at which it entered. It should be immediately run over some form of cooler and its temperature reduced to an aver- age of about 40°, at which temperature it should be run into insulated cans and carried to the main creamery, where it is ripened and made into butter. It is practicable to reduce the temperature of the cream by the water section of the cooler to about 60° in the Northern States, but in the Southern States a temperature of 70° is about as low as it is practicable to lower the temperature by well water. From the temperature at which the cream leaves the water section of the cooler to a final average temperature of 40° the cooling is done in the more modern creameries by circulating low-temperature brine or water through the coils. In those localities where natural ice is available at a small cost the cooling is generally done by employing a mixture of salt and ice. In the Southern States, however, where natural ice ty } } q —— ee aees = APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 87 is not available and the cost of manufactured ice is too great for economical use, mechanical refrigeration is desirable in order to reduce the temperature of the cream to a point where it can safely be carried to the main creamery. Due to the development of the hand separator, by the use of which the farmer is enabled to separate his milk on the farm, the auxiliary creamery is fast being done away with. This arrangement, however, places the responsibility of properly cooling the cream upon the farmers before it is hauled or shipped to the creamery. What has been said on the subject of cooling milk on the farm is, of course, applicable to the cooling of cream, and as the weight of cream is only about 13 per cent of that of the whole milk, the one is a com- paratively easy matter. Where the separating is done at the auxiliary creamery the ae is first heated to about 90° before being run through the separator. The temperature of the cream is first reduced by the well-water section of the cooler to approximately 60°. Assuming that the auxiliary creamery handles 1,500 pounds of cream daily through the summer months, and the temperature of the cream when received is 60°, and that it is cooled to an average tem- perature of 40°, the refrigeration necessary to cool the cream is 1,500 x .90(60—40) = 27,000 B. T. U. But there is the loss in cooling brine, radiation, etc., that must be taken into consideration. Owing to the variation due to poor workmanship, the arrangement of the apparatus, etc., it is impracticable to calculate very closely on the amount of refrigeration that will be lost. Therefore it is cus- -tomary to allow a certain amount to cover this loss, which usually varies from 25 to 50 percent. In the case under consideration 25 pe1 cent would be ample. During the summer months the machine would be run about 6 hours per day; therefore the size of machine necessary would be AGEN ete cor ton. A cubic foot of calcium-chlorid brine will absorb about 52 B. T. U. in rising 1° F., and allowing a 10-degree rise in brine, 30 to 40 degrees, each cubic foot will absorb 52(40—30) =520 B.T.U. Therefore the oo =52 cubic feet, providing the machine is not running during the cooling process. But with the machine in operation the volume of brine will be con- siderably less. A half-ton machine is capable of extracting 6,000 B. T. U. per hour. Consequently as the machine is run during the two hours of cooling it will extract 12,000 B. T. U. and the volume : 2; 0x 1.25) —12,000 : of brine necessary will be OS es cubic feet. As the amount of heat that will come through the walls of the brine tank is directly proportional to the exposed outside surface, and as volume of brine required for cooling the cream 1s 88 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE. the cost of insulation also varies in the same proportion, it is obvious that the brme tank should be constructed in the form of a cube which gives the least exposed surface for a given volume of any form of rectangular tank. The brine tank should be in the form of a cube with 3-foot 8-inch sides, giving a surface of 80 square feet. The tank should be insu- lated for a heat transmission of not over 2 B. T. U. per square foot, per 24 hours per degree difference between the inside and outside temperature. MARKET CREAM PLANT. The market cream plant, as the name implies, handles only sweet cream for the market. The plant is usually provided with churns in order to make butter from any soured cream that may accumulate, otherwise the equipment consists of that necessary for pasteurizing and cooling. The method of operating a plant of this kind 1s essentially the same as that employed in operating a regular local creamery; that is, the plant is located on a railroad where good connections are had with the markets. The milk or cream is received from the producers or auxiliary creameries, usually early in the morning, and is pasteurized and refrigerated immediately. In a market cream plant it is impera- tive that the work be done quickly and thoroughly in order to get the cream on the market in perfect condition. In this type of plant refrigeration is of the utmost importance, as the safe handling of the cream depends more on the proper cooling than any other one feature of the business. The amount of refrigeration required in the market cream plant is of course considerably more than that for a creamery handling the same amount of cream for butter making, as the temperature main- tained for market cream is considerably lower. In ripening cream for butter making it is seldom that its temperature is allowed to go below 50° F., about 65° F. being the usual ripening temperature. With cream intended for the market, however, a temperature of just above the freezing point is desired. Shipping facilities often require the holding over of one day’s supply of cream to the morning of the following day, consequently suitable provision for cold storing must be provided. What has already been said on the cooling, storing, and shipping of milk is of course applicable to cream. ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT 10 CENTS PER COPY V : WASHINGTON : GOVERNMENT PRINTING OFFICE : 1614 ~~ 7 eee eee a * | : : : é w ; i = s | 5 ; ». + ; 3 :: i : f aie 4 " ‘