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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 = <n OU ee peta: 145. 4 6320 eerie sah eleceeee eee 72 86. 0 30.0 O2i | toe eee . 88 150. 8 66. 0 Of Noe ss eas ane |Soce eens 89.6 S2NON aaa ee Re OVE ete

The curves, figure 1, show the specific heat of 34 per cent milk and 20 and 40 per cent cream at different temperatures between 35.6° F. and 150.8° F.

COHESION AND VISCOSITY OF MILK.

Milk upon cooling assumes a denser semiliquid aspect and sticks more closely to the walls of the vessel than when warm. Conse- quently it is harder to clean, by means of water, a vessel that has contained cold milk than one that has contained warm milk. On the other hand, for the same reason, it is more difficult to cleanse vessels that have contained milk by the use of cold water than by the use of warm water. Milk is more lable to foam when cold than when hot, and the foam will keep longer. The foam, however, will disappear if the milk is heated. With the lowering of the temperature of milk the cohesion increases in proportion to its viscosity.

At 86° F. the viscosity is about 1.7 times as great in milk as it is in water, while at 32° F. its viscosity is about 2.4 times that of water. At 32° F. the viscosity of milk is about 2.6 times as great as it is at 86° F.

APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 5

Freshly drawn milk shows a smaller viscosity than it does after being allowed to stand for some time. It is a well-known fact that

the viscosity plays an important part in the formation of cream and in the skimming of milk.

COEFFICIENT OF EXPANSION OF MILK AND CREAM.

In Table II is given the change in the volume of milk and cream with varying percentages of fat and degrees of temperature. The

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SPECIFIC HEAT e) ee Ee i we ts Pee ee hee aul

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/48

Fia. 1.—Curves showing the specific heat of milk, 20 per cent and 40 per cent cream at different tem- peratures.

percentage of fat varies in steps of 1 per cent from skimmed milk to double cream, and determination of change in volume has been made in steps of 2° F. from 50 to 140° F. A temperature of 68° I’. (20° C.) has been taken as the basis and the change in volume reckoned from this temperature. These tentative determinations and those on spe- cific gravity were made by the Division of Weights and Measures of the United States Bureau of Standards.

6 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE,

TABLE I1.— Volume ! of milk and cream at various temperatures occupied by unit volume at 68° F. (20° C.).

Per Temperature (° F.).

52 | 54 | 50 7 iepeos | 60 | 62 | 64 | 66 | 68 | 70 | 72

fat. Volume.

0. 025 0.9980 | 0. 9980 | 0.9985 | 0.9985 | 0.9990 | 0.9990 |0.9990 | 0.9995 | 0.9995

1.0000 | 1.0000 | 1.0005

1| .9980 | .9980} .9985| .9985]| .9990| .9990 | .9990| .9995} .9995 | 1.0000 | 1.0000 | 1.0005

2) .9975| .9975 | .9980} .9980} .9985 | .9990} .9990} .9995| .9995 | 1.0000 | 1.0000 | 1.0005

3} .9975| .9975| .9980 | ~.9980} .9985 | .9990 | .9990} .9995| .9995 | 1.0000 | 1.0000 | 1.0005

4} .9975| .9975] .9980| .9980} .9985 | .9985] .9990| .9995 | .9995 | 1.0000 | 1.0000 | 1.0005

5} .9975| .9975} .9980| .9980}] .9985 | .9985 | .9990| .9995 | .9995} 1.0000 | 1.0000 | 1.0005

6} .9970| .9975} .9975] .9980| .9980} .9985 | .9990| .9995 | .9995 | 1.0000 | 1.0000 | 1.0005

7| .9970} .9970| .9975} .9975 | .9980| .9985 | .9985 | .9990} .9995 | 1.0000 | 1.0000 | 1.0010

8} .9970| .9970; .9975}| .9975} .9980|) .9985 | .9985} .9990| .9995 | 1.0000} 1.0005 | 1.0010

9| .9965}] .9965}; .9970) .9975} .9980} .9985 | .9985 | .9990| .9995 | 1.0000 | 1.0005 | 1.0010

10] .9965} .9965|) .9970} .9975} .9980| .9985 | .9985} .9990} .9995 | 1.0000 | 1.0005 | 1.0010 11 | .9965} .9965| .9970| .9975| .9980} .9985]| .9985 | .9990| .9995 | 1.0000 | 1.0005 | 1.0010 12] .9955| .9960} .9965] .9970|] .9975 | .9980; .9985| .9990] .9990 | 1.0000 | 1.0005 | 1.0010 13 | .9955| .9960} .9965| .9970] .9975} .9980} .9985| .9990| .9990 | 1.0000 | 1.0005 | 1.0010 14} .9950} .9955| .9960| .9970] .9975}| .9980]| .9985 | .9990| .9990 | 1.0000 | 1.0005 | 1.0010 15| .9950}] .9955} .9960| .9970|] .9975} .9980} .9985 |) .9990 | .9990] 1.0000 | 1.0005 | 1.0010 16 | .9950 | .9955; .9955 1 .9965{] .9970) .9980]| .9985! .9990| .9990 | 1.0000 | 1.0005 | 1.0010 17| .9945| .9950} .9955 | .9965} .9970| .9980} .9985 | .9990} .9990| 1.0000 | 1.0005 | 1.0010 18 | .9940} .9945) .9950| .9960] .9970| .9980} .9980] .9985] .9990 | 1.0000 |} 1.0005 | 1.0010 19; .9940| .9945} .9950} .9960} .9970] .9975 | .9980] .9985] .9990]) 1.0000 | 1.0005 | 1.0010 20 | .9930| .9940 |—-.9945 | .9955| .9965 | .9975} .9980| .9985} .9990]} 1.0000 | 1.0005 | 1.0010 21} .9980} .9940} .9945] .9955| .9965 | .9975 |} .9980; .9985] .9990} 1.0000 | 1.0005 | 1.0010 22; .9930|) .9940| .9945| .9955| .9965 | .9975 | .9980} .9985| .9990 | 1.0000 | 1.0010 | 1.0015 23.| .9930|) .9940] .9940| .9955| .9965 | .9975 | .9980; .9985 1 .9990 | 1.0000 | 1.0010 | 1.0015 24} .9925|) .9930| .9940} .9950| .9960| .9975) .9975 | .9985] .9990} 1.0000 | 1.0010 | 1.0015 25} .9925| .9930| .9940| .9950} .9960] .9970] .9975} .9985] .9990 | 1.0000 | 1.0010 | 1.0015 26} .9925) .9930} .9940} .9950| .9960| .9970} .9975| .9985 | .9990} 1.0000 | 1.0010 | 1.0015 27| .9925|] .9930|) .9940} .9950} .9960] .9970} .9975]| .9985] .9990 | 1.0000 | 1.0010 | 1.0015 28 | .9915| .9925) .9935 | .9945 |] .9955 | .9965] .9975]| .9980) .9990} 1.0000 |} 1.0010 | 1.0015 29| .9915| .9925| .9935 | .9945 | .9955 |} .9965| .9975] .9980] .9990 | 1.0000 | 1.0010 | 1.0015 30} .9915| .9925) .9935 | .9945 | .9955| .9965} .9970] .9980) .9990} 1.0000 | 1.0010 | 1.0020 31} .9915] .9925|) .9935) .9945 | .9955| .9965} .9970} .9980) .9990} 1.0000 | 1.0010 | 1.0020 32] .9910| .9920} .99380} .9940 | .9950} .9960] .9970}] .9980) .9990 | 1.0000 | 1.0010 | 1.0020 33} .9910| .9920| .9930} .9940] .9950) .9960} .9970} .9980} .9990 | 1.0000 | 1.0010 | 1.0020 34] .9910|) .9915 | .9925} .9940] .9950| .9960| .9970}; .9980} .9990 | 1.0000 | 1.0010 | 1.0020" 35 | .9900| .9915 | .9925] .9940 |} .9940} .9960| .9970] .9980} .9990} 1.0000 | 1.0010 | 1.0020 36} .9900| .9910|} .9920} .9930|] .9940) .9955 | .9965 | .9980} .9990 | 1.0000 | 1.0010 | 1.0025 37} .9890} .9910}) .9920} .9930} .9940) .9955 | .9965 |; .9980} .9990 | 1.0000 | 1.0010 | 1.0025 38] .9890|] .9910) .9920} .9930] .9940} .9955] .9965 | .9980] .9990 | 1.0000 | 1.0010 | 1.0025 39} .9890} .9900} .9915} .9925} .9940} .9955 | .9965) .9975 | .9990 | 1.0000 | 1.0010 | 1.0025 40} .9890} .9900} .9915| .9925] .9940] .9950| .9960| .9975] .9990 | 1.0000 | 1.0010 | 1.0025

1 The tabulated values are given to the nearest 0.0005.

APPLICATION OF REFRIGERATION TO HANDLING OF MILK. i

TaBLE II.— Volume of milk and cream at various temperatures occupied by unit volume

at 68° F. (20° C.)—Continued.

0. 025

Temperature (° F.).

74 | 76 | 78 | 80 | 82 | 84 | 86 | 88 | 90 | 92 | 94 | 96 Volume. = 1.0005 | 1.0010 | 1.0010 | 1.0015 | 1.0020 | 1.0025 | 1.0030 |1.0030 | 1.0035 | 1.0040 | 1.0045 | 1.0050 1.0005 | 1.0010 | 1.0010 | 1.0015 | 1.0020 ) 1.0025 | 1.0030 |1. 0030 | 1.00385 | 1.0040 | 1.0045 | 1.0050 1.0010 | 1.0010 | 1.0015 | 1.0020 | 1.0020 | 1.0025 | 1.0030 |1. 0035 | 1.0040 | 1.0040 | 1.0045 | 1.0050 1.0010 | 1.0010 | 1.0015 | 1.0020 | 1.0020 | 1.0025 | 1.0030 |1. 0035 | 1.0040 | 1.0045 | 1.0045 | 1.0055 1.0010 | 1.0010 | 1.0015 | 1.0020 | 1.0020 | 1.0025 | 1.0030 |1. 0035 | 1.0040 | 1.0045 | 1.0050 | 1. 0055 1.0010 | 1.0015 | 1.0020 | 1.0020 | 1.0025 | 1.0030 | 1.0035 |1. 0085 | 1.0045 | 1.0045 | 1.0050 | 1. 0055 1.0010 | 1.0015 | 1.0020 | 1.0020 | 1.0025 | 1.0030 | 1.0035 |1.0040 | 1.0045 | 1.0050 | 1.0050 | 1. 0060 1, 0010 | 1.0015 | 1.0020 | 1.0025 | 1.0025 | 1.0030 | 1.0035 |1.0040 | 1.0045 | 1.0050 | 1.0055 | 1.0060 1.0010 | 1.0015 | 1.0020 | 1.0025 | 1.0030 | 1.0030 | 1.0035 |1. 0040 | 1.0045 | 1.0050 | 1.0055 | 1.0060 1.0010 | 1.0015 | 1.0020 | 1.0025 | 1.0030 | 1.0035 | 1.0040 |1. 0045 | 1.0050 | 1.0055 | 1.0060 - 1. 0065 1.0015 | 1.0020 | 1.0025 | 1.0025 | 1.0030 | 1.0035 | 1.0040 |1.0045 | 1.0050 | 1.0055 | 1.0060 | 1.:0065 1.0015 | 1.0020 | 1.0025 | 1.0025 | 1.0030 | 1.0035 | 1.0040 |1.0045 | 1.0055 | 1.0055 | 1.0065 | 1.0070 1.0015 | 1.0020 | 1.0025 | 1.0030 | 1.0030 | 1.0035 | 1.0040 |1.0050 | 1.0055 | 1.0060 | 1.0065 | 1.0070 1.0015 | 1.0020 | 1.0025 | 1.0030 | 1.0035 | 1.0040 | 1.0045 |1.0050 | 1.0055 | 1.0060 | 1.0065 | 1.0070 1.0015 | 1.0020 | 1.0025 | 1.0030 | 1.00385 | 1.0040 | 1.0045 |1.0050 | 1.0055 | 1.0065 | 1.0070 | 1.0075 1.0015 |. 1. 0025 | 1.0030 | 1.0030 | 1.0035 | 1.0040 | 1.0045 |1.0055 | 1.0060 | 1.0065 | 1.0070 | 1.0075 1.0015 | 1.0025 | 1.0030 | 1.0035 | 1.0040 | 1.0045 | 1.0050 |1.0055 | 1.0060 | 1.0070 | 1.0075 | 1.0080 1.0015 | 1.0025 | 1.0030 | 1.0035 | 1.0040 | 1.0045 | 1.0050 |1. 0060 | 1.0060 | 1.0070 | 1.0075 | 1. 0080 1.0020 | 1.0025 | 1.0030 | 1.0035 | 1.0040 | 1.0045 | 1.0055 |1. 0060 | 1.0065 | 1.0075 | 1.0080 | 1.0085 1.0020 | 1.0025 | 1.0030 | 1.0035 | 1.0045 | 1.0045 | 1.0055 |1. 0060 | 1.0065 | 1.0075 | 1.0080 | 1. 0085 1.0020 | 1.0025 | 1.0030 | 1.0035 | 1.0045 | 1.0050 | 1.0055 |1. 0060 | 1.0070 | 1.0075 | 1.0085 | 1.0090 - 1.0020 | 1.0025 | 1.0030 | 1.0040 | 1.0045 | 1.0050 | 1.0060 |1.0065 | 1.0070 | 1.0080 | 1.0085 | 1.0090 1. 0020 | 1.0030 | 1.0035 | 1.0040 | 1.0050 | 1.0055 | 1.0060 |1. 0065 | 1.0075 | 1.0080 | 1.0090 | 1.0095 1. 0020 | 1.0030 | 1.0035 | 1.0040 | 1.0050 | 1.0055 | 1.0065 |1.0070 | 1.0075 | 1.0085 | 1.0090 | 1.0095 1. 0020 | 1.0030 | 1.0035 | 1.0040 | 1.0050 | 1.0060 | 1.0065 |1.0070 | 1.0080 | 1.0085 } 1.0095 | 1.0100 1. 0020 | 1.0030 | 1.0035 | 1.0045 | 1.0055 | 1.0060 | 1.0070 |1.0075 | 1.0080 | 1.0090 } 1.0095 | 1.0105 1. 0025 | 1.0030 | 1.0040 | 1.0045 | 1.0055 | 1.0060 | 1.0070 |1. 0080 | 1.0085 | 1.0090 | 1.0100 | 1.0110 1. 0025 | 1.0030 | 1.0040 | 1.0045 | 1.0055 | 1.0060 | 1.0070 |1. 0080 | 1.0085 | 1.0095 | 1.0100 | 1.0110 1. 0025 | 1.0030 | 1.0040 | 1.0045 | 1.0055 | 1.0065 | 1.0075 |1. 0080 | 1.0090 | 1.0095 | 1.0105 | 1.0115 1. 0025 | 1.0030 | 1.0040 | 1.0050 | 1.0060 } 1.0065 | 1.0075 |1. 0080 | 1.0090 | 1.0095 | 1.0105 | 1.0115 1.0025 | 1.0035 | 1.0045 | 1.0050 | 1.0060 | 1.0065 | 1.0080 |1.0085 | 1.0095 | 1.0100 } 1.0110 | 1.0120 1. 0025 | 1.0035 | 1.0045 | 1.0050 | 1.0060 | 1.0065 | 1.0080 1.0085 | 1.0095 | 1.0100 | 1.0110 | 1.0120 1.0030 | 1.0035 | 1.0045 | 1.0055 | 1.0065 | 1.0070 | 1.0085. |1.0090 | 1.0100 | 1.0105 | 1.0115 | 1.0125 1.0030 | 1.0035 | 1.0045 | 1.0055 | 1.0065 | 1.0070 | 1.0085 |1.0090 | 1.0100 | 1.0105 } 1.0115 | 1.0125 1.0030 | 1.0040 | 1.0050 | 1.0055 } 1.0065 | 1.0075 | 1.0085 |1..0095 | 1.0105 | 1.0110 | 1.0120 | 1.0130 1.0030 } 1.0040 | 1.0050 | 1.0060 } 1.0070 | 1.0075 | 1.0090 ]1.0095 | 1.0105 | 1.0110 | 1.0120 | 1.0130 1.0035 | 1.0045 | 1.0055 | 1.0060 } 1.0070 | 1.0080 | 1.0090 1.0100 | 1.0110 | 1.0115 | 1.0125 | 1.0135 1.0035 | 1.0045 | 1.0055 | 1.0060 } 1.0070 | 1: 0080 | 1.0095 |1..0100 | 1.0110 | 1.0115 | 1.0125 | 1.0135 1.0035 | 1.0045 | 1.0055 | 1.0065 | 1.0075 | 1.0085 | 1.0095 |1.0100 | 1.0115 | 1.0120 | 1.0130 | 1.0140 1.0035 | 1.0045 | 1.0055 | 1.0065 | 1.0075 | 1.0085 | 1.0095 |1.0105 | 1.0115 | 1.0120 | 1.0130 | 1.0140 1.0035 | 1.0045 | 1.0055 | 1.0065 | 1.0075 | 1.0085 | 1.0095 |1.0105 | 1.0115 | 1.0125 | 1.0130 | 1.0145

———

8 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE.

TaBLE II.— Volume of milk and cream at various temperatures occupied by unit volume _at 68° F. (20° C.)—Continued.

Temperature (° F.).

Percentage | of butter fat. 98 | 100 | 102 | 104 106 | 108 | 110 | 112 | 114 | 116 | 118 Volume.

0.025 | 1.0055 | 1.0060 | 1.0065 | 1.0070 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100} 1.0105 1} 1.0055 | 1.0060 | 1.0065 | 1.0070 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100 | 1.0105 2 | 1.0055 | 1.0060 | 1.0065 | 1.0070 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100] 1.0110 3 | 1.0060 | 1.0065 | 1.0065 | 1.0070 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100] 1.0110 4 | 1.0060 | 1.0065 | 1.0065 | 1.0070 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100} 1.0110 5 | 1.0060 } 1.0065 | 1.0070 | 1.0075 | 1.0080 | 1.0085 | 1.0085 | 1.0090 | 1.0095 | 1.0100} 1.0110 6 | 1.0060 } 1.0065 | 1.0070 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0090 | 1.0095 | 1.0100} 1.0110 7 | 1.0065 | 1.0070 | 1.0075 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100 | 1.0105} 1.0115 8 | 1.0065 | 1.0070 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100 | 1.0105 | 1.0110] 1.0115 9 | 1.0065 | 1.0070 | 1.0080 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100 | 1.0105 | 1.0110} 1.0115 10 | 1.0070 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0090 | 1.0095 | 1.0100 | 1.0105 | 1.0110} 1.0115 11 | 1.0070 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0095 | 1.0100 | 1.0105 | 1.0110} 1.0115

12 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0095 | 1.0105 | 1.0110 | 1.0115 | 1.0120} 1.9125 13 | 1.0075 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100 | 1.0105 | 1.0110 | 1.0115 | 1.0120} 1.0125 14 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100 | 1.0100 | 1.0110 | 1.0115 | 1.0120 | 1.0125] 1.0130 15 | 1.0080 | 1.0085 | 1.0090 | 1.0095 | 1.0100 | 1.0105 | 1.0110 | 1.0115 | 1.0120 | 1.0125] 1.0130 16 | 1.0085 | 1.0090 | 1.0095 | 1.0100 | 1.0105 | 1.0110 | 1.0115 | 1.0120 | 1.0125 | 1.0130 | 1.0135 17 | 1.0085 | 1.0090 | 1.0095 | 1.0105 |} 1.0105 | 1.0115 | 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140 18 | 1.0090 | 1.0095 | 1.0100 | 1.0105 | 1.0110 | 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140} 1.0145 19 | 1.0090 | 1.0095 | 1.0100 | 1.0110 | 1.0115 | 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140} 1.0145 20 | 1.0095 | 1.0100 | 1.0105 | 1.0110 | 1.0115 | 1.0125 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0150 21 | 1.0095 | 1.0100 | 1.0105 | 1.0115 | 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0145 | 1.0150 | 1.0155 22 | 1.0100 | 1.0105 | 1.0110 } 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140 | 1.0150 |} 1.0155 | 1.0160 23 | 1.0105 | 1.0105 | 1.0115 } 1.0120 | 1.0125 | 1.0130 | 1.0140 | 1.0145 | 1.0150 | 1.0155 | 1.0160 24 | 1.0105 | 1.0110 | 1.0120 } 1.0125 | 1.0130 | 1.0135 | 1.0145 | 1.0150 | 1.0155 | 1.0160 | 1.0165 25 | 1.0110 | 1.0115 | 1.0120 } 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0150 | 1.0160 | 1.0165 1.0170 26 | 1.0115 | 1.0120 | 1.0125 | 1.0135 | 1.0140 | 1.0145 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0180 27 | 1.0115 | 1.0120 | 1.01380 | 1.0135 | 1.0140 | 1.0150 | 1.0155 | 1.0160 | 1.0170 | 1.0170} 1.0180 28 | 1.0120 | 1.0125 | 1.0130 | 1.0140 | 1.0145 | 1.0150 | 1.0160 | 1.0165 | 1.0175 | 1.0175 | 1.0185 29 | 1.0120 | 1.0130 | 1.0135 |} 1.0140 | 1.0150 | 1.0155 | 1.0160 | 1.0165 | 1.0175 | 1.0180} 1.0185 30 | 1.0125 | 1.0130 | 1.0135 | 1.0145 | 1.0155 | 1.0155 | 1.0165 | 1.0170 | 1.0175 | 1.0180 | 1.0190 31 | 1.0125 | 1.0135 | 1.0140 | 1.0145} 1.0155 | 1.0160 | 1.0170 | 1.0175 } 1.0180 | 1.0185 | 1.0190 32 | 1.0130 | 1.0135 | 1.0140 | 1.0150 | 1.0160 | 1.0165 | 1.0170 | 1.0180 | 1.0185 | 1.0190 | 1.0195 33 | 1.0130 | 1.0140 | 1.0145 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0180 | 1.0185 | 1.0190 | 1.0195 34 | 1.0135 | 1.0140 | 1.0150 | 1.0160 | 1.0165 | 1.0170 | 1.0175 | 1.0185 | 1.0190 | 1.0195 | 1.0200 35 | 1.0135 | 1.0145 | 1.0150 | 1.0160 | 1.0165 | 1.0170 | 1.0180 | 1.0190 | 1.0195 | 1.0200 | 1.0205 36 | 1.0140 | 1.0145 | 1.0155 | 1.0165 | 1.0170 | 1.0175 | 1.0185 | 1.0195 | 1.0200 | 1.0205 | 1.0210 37 | 1.0145 | 1.0150 | 1.0160 | 1.0165 | 1.0175 | 1.0180 | 1.0185 | 1.0195 | 1.0200 | 1.0205} 1.0210 38 | 1.0150 | 1.0155 | 1.0165 | 1.0170 | 1.0175 | 1.0185 | 1.0190 | 1.0200 | 1.0210 | 1.0215] 1.0215 39 | 1.0150 | 1.0160 | 1.0165 | 1.0170 | 1.0180 | 1.0185 | 1.0195 | 1.0205 | 1.0210 | 1.0215 | 1.0220 40 | 1.0155 | 1.0165 | 1.0170 | 1.0175 | 1.0185 | 1.0190 | 1.0200 | 1.0210 | 1.0215 | 1.0220 | 1.0230

APPLICATION OF REFRIGERATION TO HANDLING OF MILK.

9

TaBLE II.— Volume of milk and cream at various temperatures occupied by unit volume

Percentage

of butter fat.

i=) oO iw) on

OonronaPrwhyore

EL fh ek ek en pt ek ek a tet fed et fe et fet et tet at et et et et et at et eat pet et pet et pat eat et tt tt

at 68° F. (20° C.)—Continued.

(Temperature (° F.).

120 | 122 | 124 | 126 | 128 | 130 | 132 | 134 | 136 | 138 | 140 Volume.

0110 | 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0155 | 1.0160 | 1.0170 | 1.0175 0110 | 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0155 | 1.0160 | 1.0170 | 1.0175 0115 | 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0155 | 1.0160 | 1.0170 | 1.0175 0115 | 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0155 | 1.0160 | 1.0170 | 1.0175 0115 | 1.0120 |} 1.0125 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0155 | 1.0166 | 1.0170 | 1.0175 0115 } 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0155 | 1.0160 | 1.0170 | 1.0175 0115 | 1.0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0155 | 1.0160 | 1.0170 | 1.0175 0120 | 1.0125 | 1.01380 | 1.0135 | 1.0140 | 1.0145 | 1.0150 | 1.0155 | 1.0160 | 1.0170 | 1.0175 0120 | 1.0125 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0150 | 1.0155 | 1.0165 | 1.0170 | 1.0175 0120 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | “1.0180 0120 | 1.0130 | 1.0135 | 1.0140 } 1.0145 | 1.0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0180 0120 | 1.0130 | 1.0135 | 1.0140 | 1.0145 | 1.0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0180 0130 | 1.0135 | 1.0140 | 1.0145 | 1.0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 |} 1.0175 | 1.0180 0130 | 1.0135 | 1.0140 | 1.0145 | 1.0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0175 | 1.0180 0135 | 1.0140 | 1.0145 | 1.0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0175 | 1.0180] 1.0185 0135 | 1.0140 | 1.0145 | 1.0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0175 | 1.0180] 1.0185 .0140 | 1.0145 | 1.0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0175 ) 1.0180 | 1.0185 | 1.0190 .0145 | 1.0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0175 | 1.0175-| 1.0180 | 1.0185 | 1.0190 0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0175 | 1.0180 | 1.0185 | 1.0185 | 1.0190 | 1.0195 0150 | 1.0155 | 1.0160 | 1.0165 | 1.0170 | 1.0175 | 1.0180 | 1.0185 | 1.0185 | 1.0190 | 1.0195 0155 | 1.0160 | 1.0165 ; 1.0170 | 1.0175 | 1.0180 | 1.0185 | 1.0190 | 1.0195 | 1.0200 | 1.0205 0160 | 1.0165 | 1.0170 | 1.0175 | 1.0180 | 1.0185 | 1.0190 | 1.0190 | 1.0195 | 1.0200 | 1.0205 0165 | 1.0170 | 1.0175 | 1.0180 | 1.0185 | 1.0190 | 1.0190 } 1.0195 | 1.0200 | 1.0205 | 1.0210 0165 | 1.0170 | 1.0175 | 1.0180 | 1.0185 | 1.0190 | 1.0195 | 1.0195 | 1.0200 | 1.0205 | 1.0210 0170 | 1.0180 | 1.0185 | 1.0190 | 1.0195 | 1.0200 | 1.0205 | 1.0205 | 1.0210 | 1.0215 } 1.0220 0175 | 1.0180 | 1.0185 | 1.0190 | 1.0195 | 1.0200 | 1.0205 |} 1.0210 | 1.0215 | 1.0220 | 1.0225 0185 | 1.0190 | 1.0195 | 1.0200 | 1.0205 | 1.0210 | 1.0215 | 1.0220 | 1.0225 | 1.0230} 1.0235 0185 | 1.0190 | 1.0195 | 1.0200 | 1.0205 | 1.0210 | 1.0215 | 1.0220 | 1.0225 | 1.0230] 1.0235 0190 | 1.0200 | 1.0205 | 1.0210 } 1.0215 | 1.0220 | 1.0225 | 1.0230 | 1.0235 | 1.0240] 1.0245 0195 | 1.0200 | 1.0205 | 1.0210 | 1.0215 | 1.0220 | 1.0225 | 1.0230 | 1.0235 | 1.0240 | 1.0245 0195 | 1.0200 | 1.0205 ; 1.0210 |.1.0215 | 1.0220 | 1.0225 | 1.0235 | 1.0240 | 1.0245] 1.0250 0200 | 1.0205 | 1.0210 | 1.0215 | 1.0220 | 1.0225 | 1.0230 | 1.0235 | 1.0240 | 1.0245 | 1.0250 0205 | 1.0210 | 1.0215 | 1.0220 | 1.0225 | 1.0230 | 1.0235 | 1.0240 | 1.0245 | 1.0250 | 1.0255 0205 | 1.0210 | 1.0215 | 1.0220 | 1.0225 | 1.0230 | 1.0235 | 1.0240 | 1.0245 | 1.0250] 1.0255 0210 | 1.0215 | 1.0220 | 1.0225 | 1.0230 | 1.0240 | 1.0245 | 1.0245 | 1.0250 | 1.0255 | 1.0260 0210 | 1.0215 |} 1.0220 | 1.0225 | 1.0230 | 1.0240 | 1.0245 | 1.0250 | 1.0250 | 1.0255 | 1.0260 0215 | 1.0225 | 1.0230 | 1.0235 | 1.0240 | 1.0245 | 1.0250 | 1.0255 | 1.0260 | 1.0265} 1.0270 0215 | 1.0225 | 1.0230 | 1.0235 | 1.0240 | 1.0245 | 1.0250 | 1.0255 | 1.0260 | 1.0265 | 1.0270 0220 | 1.0230 | 1.0235 | 1.0240 | 1.0245 | 1.0250 | 1.0255 | 1.0260 | 1.0265 | 1.0270} 1.0280 0225 | 1.0235 | 1.0240 | 1.0245 | 1.0250 | 1.0255 | 1.0260 | 1.0265 | 1.0270 | 1.0275} 1.0280 0235 | 1.0240 | 1.0245 | 1.0255 | 1.0260 | 1.0265 | 1.0270 | 1.0275 | 1.0280 | 1.0285 | 1.0290

10 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE.

SPECIFIC GRAVITY OF MILK AND CREAM.

Table III covers the specific gravity of milk and cream determined at 68° F. (20° C.) in terms of water at the same temperature as unity.

Tasie III.—Specific gravity of milk and cream corresponding to various percentages of butter fat at 68° F.

Per- : Per- : er F Per = ific Specific Specific Specific

centage ibe _ {| centage : centage -,. || centage aa of fat. | ST@VICY- || of fat. | STAVILY- Il offat. | STaVILY- |) of tat. | Stavity- 0. 025 1.037 |} il 1.024 21 1.012 31 1. 003 1.036 || 12 1.022 22 1.011 32 1.002

2 1.035 13 1.020 23 1.010 33 1.001

3 1.034 14 1.019 24 1.009 34 1.000

4 1.032 15 1.018 25 1.008 35 . 999

5 1.031 16 1.017 26 1.008 36 . 999

6 1.030 17 1.016 27 1.007 37 . 998

7 1.029 18 1.015 28 1.006 38 . 997

8 1.027 19 1.014 29 1.005 39 . 996

9 1.026 20 1.013 30 1.004 40 . 995

10 1.025

FREEZING POINT OF MILK.

The freezing point of milk depends upon its composition, but is always lower than that of water. The freezing point of market milk generally varies from 31° to 29° F. The addition of water to milk serves to raise the freezing point toward that of pure water, 32° F., while, on the other hand, the addition of fats, solids, ete., tends to lower the freezing point, as does also the increase in acidity. Upon these variations 1n the freezing point is based the cryoscopical method of determining the addition of water to milk.

EFFFECT OF FREEZING ON MILK.

While the action of cold on milk at a temperature above the freezing point has no other effect than that of varying the density and vis- cosity, at a temperature below the freezing point it changes the chemical and physical composition.

According to Kasdorf,! when raw milk which was partly frozen at a temperature of 10.5° F., in the ordinary container, during trans- portation, it was found that ice first formed around the sides and at the bottom of the can; the central core contained most of the casein, sugar, and other mineral ingredients, while most of the fat was found in the top layer of the liquid portion.

When milkhas been frozen gradually, without agitation, and thawed out clots will be found floating in the liquid, composed mostly of albumen and fat, which may be dissolved by cooking; on the other hand, if the milk is preserved in a frozen condition for three or four weeks these clots will be very hard to dissolve, and the difficulty experienced in dissolving them increases as the length of time the

1 Kasdorf, Otto. Eis und Kialte in Molkereibetrieb. Leipzig, 1904, p. 20.

APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 11

milk is preserved in a frozen state. For this reason the freezing of milk, for the purpose of transportation, has hitherto been little used.

If the milk is held at 32° F. for a few days, some types of bacteria may grow and multiply slowly. With a good quality of milk, i. e., that containing few bacteria, it may take weeks or even months for them to gain great headway. What few bacteria develop at low tem- peratures are of different species from those ordinarily found at the higher temperatures, and they may produce marked changes in the chemical composition of the milk without especially changing its ap- pearance. Consequently, it is unsafe to assume that milk which has been held for several days at a low temperature is in good condition. According to Pennington' milk exposed continually to atemperature of 29° to 32° F. causes, after a lapse of from 7 to 21 days, the formation of small ice crystals which gradually increase until the milk is filled with them, and there may be an adherent layer on the walls of the vessel. The milk does not freeze solid. In spite of the fact that the milk was a semisolid mass of ice crystals, an enormous increase in bacterial content took place. Though the bacterial content was numerically in the hundreds of millions per cubic centimeter, there was neither taste nor odor to indicate that such was the case. Neither did the milk curdile when heated, and the unfitness of the milk for household purposes would not ordinarily be detected until the lactic acid bacteria decreased in numbers and the putrefactive bacteria began to develop.

THE INFLUENCE OF TEMPERATURE ON THE BACTERIOLOGICAL FLORA OF MILK.

Each species of bactertum found in milk and each particular variety has an upper and lower temperature limit beyond which it does not erow, and a certain temperature, called the optimum, at which it grows best.

The optimum temperature of most forms occurring in milk is between 70° and 100° F. As the temperature of milk is lowered the rate of growth is diminished until at 40° F. the multiplication is very slow and at a temperature just above the freezing point the develop- ment practically ceases; in fact, there is an apparent decrease in the number, at least for a short time. The action of cold at this tem- perature, however, does not totally destroy life in the bacteria, but - causes them to lie dormant. When the temperature of the milk is raised they again begin to multiply. As an illustration of the relative variation in the growth of bacteria in milk held at different temper- atures, one writer gives the data found in Table IV, in which 1 1s assumed to represent the number of bacteria in the fresh milk, and the relative numbers which will be found at the end of 6, 12, 24, and 48 hours, at the two temperatures, are shown in the succeeding col-

1 Pennington, Mary E. Bacterial growth and chemical changes in milk kept at low temperatures, Journal of Biological Chemistry, vol. 4, nos. 4 and 5, pp. 353-393. Baltimore, 1908.

12 BULLETIN 98, U. S. DEPARTMENT OF AGRICULTURE.

umns. These figures are based on a number of actual counts and illustrate the effect of a difference of 18° on the multiplication of bacteria. If the milk had contained at the beginning 1,000 bacteria, the part held at the lower temperature would have contained at the end of 24 hours only 4,100 bacteria, while the other would have con- tained at the same stage 6,128,000. Table V, from Bulletin 133 (Extension Bulletin 8) of the agricultural experiment station of Nebraska, illustrates the importance of holding cream at low tem- peratures.

TaBLE IV.— Multiplication of bacteria in milk held at different temperatures.*

Relative number of bacteria held at— Milk held at— 0 hours. | 6 hours. | 12 hours. | 24 hours. | 48 hours. UO ame SS ie we OY See 2 8 See cee oe, Ri a ee oo 1 122 1 4.1 6.2 Smee chy Bee ae erie a est a Pi 2 NY Se Na Ree ea 1 BS 24.2 6, 128 357, 499

1 Rogers, Lore A. Bacteria in milk. U. S. Department of Agriculture, Farmers’ Bulletin 490. Washington, D. C.

TaBLeE V.—The effect of temperature on the growth of bacteria in cream.

P Number of F Number of Temperature of cream. ime bacteria | Temperature of cream. es bacteria ; PeEnCIC es ; per c. c. a Hours. | aR: Hours | RUA OR A Re re gee eee SEE 10 3; S00) 702 52: kee ee aes Sa ae 11 188, 000 DO ee eee ee et eee eee 10 1D 580M SObs ook ean ee a eee eee -| 11 2, 631, 000 1) ae ee 8 EN ee ct rea? emit a 104 D554 20 OU aes eae Eee [eer 4, 426,000 |

THE INFLUENCE OF TIME ON THE BACTERIGLOGICAL FLORA OF MILK.

The influence of temperature and time bear certain definite rela- tions to each other; hence, a study of one necessarily includes a study of the other. Table VI serves to illustrate the effect of time as well as temperature on the keeping qualities of milk. If the table is read downward we note the effect of temperature and if read across the effect of time. When milk is first drawn from the cow it usually contains bacteria, even though it is produced under sanitary conditions, and if held at the ordinary temperature of the surrounding air in a short while the bacteria will grow and increase in numbers so rapidly that when, such milk reaches the consumer it will contain many thousand bacteria per cubic centimeter.

Conn furnishes an example of milk giving the following results:

Bacteria per c. c.

Milk drawn: ab poe ll. pai at. ees Ee eo ren eae 153, 000 Witer 1 Roar oo re hee oe ee ee ee ee 616, 000 PATO URIS - Seeee AEN. SERIE IITA | EEE Od he ee ee 539, 000 A hours: 3723-46 EE ee Pe ae Ee SE ee 680, 000 1 houre.3f425 28 be Ge a ee eee 1, 020, 000 Qos oF oe ee ee eee 2, 040, 000

WAhours:: 254 Mi geass ee a es eee B 85, 000, 000

APPLICATION OF REFRIGERATION TO HANDLING OF MILK. 13

According to Park,! two samples of milk maintained at different temperatures for 24, 48,