Fate tert eee a ase ngs Ta re raat cate raatatae u Ht at L LIBRARY NEW YORK STATE VETERINARY COLLEGE ITHACA, N. Y. iniversi Dairy chemistry, Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924000928030 DAIRY CHEMISTRY DAIRY CHEMISTRY BY HARRY SNYDER, B.S. PROFESSOR OF AGRICULTURAL CHEMISTRY, UNIVERSITY OF MINNESOTA, AND CHEMIST OF THE MINNESOTA EXPERIMENT STATION Neto Work THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., Lrp. 1911 Al rights reserved Corrrieut, 1905, By THE MACMILLAN COMPANY. Set up and electrotyped. Published December, 1905. Reprinted January, 1907 ; February, 1911. Norioood Press J. 8, Cushing & Co. — Berwick & Smith Co. Norwood, Mass., U.S.A. PREFACE Tus work is the outgrowth of a course of lec- tures given by the author for a number of years to the students of the Agricultural Department of the University of Minnesota. During recent years material progress has been made in dairying, and in writing this book it has been the aim briefly to incorporate the results of the more important investigations on the subject. In the prepara- tion of the work extensive use has been made of the bulletins and reports of the Agricultural Experiment Stations of the United States and of other works on the subject. It is the aim to present in as concise a form as possible the principal changes that take place in the handling of milk and in its manufacture into butter and cheese. While our present knowledge of some phases of the subject is incomplete, there are many facts that are known and have been found very useful as an aid in the production of dairy products of the highest sanitary and market value. It is believed that a knowledge of the general v vi PREFACE principles of dairy chemistry will be found useful alike to the farmer, to the factoryman, and to the consumer, and this work has been prepared with the view of giving information to the layman rather than to the scientist. HARRY SNYDER. CoLLEGE oF AGRICULTURE, UNIVERSITY OF MINNESOTA, St. ANTHONY Park, MINNESOTA, December 1, 1905. CONTENTS CHAPTER I Tue Composition oF MILK Complexity of composition ; Milk serum; Milk solids; Milk fats; Casein; Albumin; Milk sugar; Ash; Variations in composition of milk; Percentage composition, and total yields; First or fore milk and strippings; Milk serum, Constancy of its composition ‘ é . . CHAPTER II Mivxk Testinc Importance of milk testing ; Reliability of the Babcock test ; Sampling milk; Measuring milk with the pipette ; Mak- ing the test ; Reading the fat; Calibration of test bottles ; Speeding the machine; Centrifugal action; The acid ; Composite sample ; Testing skim milk ; Sampling frozen milk; Cleaning glassware; Water used in milk testing ; Care of test bottles and apparatus . . _ , . CHAPTER III Mick Fats Composition of fats ; Kinds of butter fats ; Palmitin ; Stearin ; Olein; Butyrin; Caproin and Caprylin; Glycerine and fatty acid content of fats; Food value of fats ; Saponifi- cation of fats; Iodine absorption of butter fats; Volatile fatty acids of butter ; Melting point and physical proper- ties of butter . @ 5 ‘ é - F vii PAGE 13 29 viii CONTENTS CHAPTER IV Tur LACTOMETER AND ITS USE IN DETERMINING M1LK ADULTERATION Quevenne’s lactometer ; Specific gravity of milk ; Influence of temperature ; Other lactometers ; Influence of skimming and watering; Calculation of solids in milk; Joint use of lactometer and Babcock test : 7 . . CHAPTER V Mitk Sucar anp Lactic Acip Physical properties of milk sugar; Fermentation of milk sugar ; Production of lactic acid in the milk ; Determin- ing the acidity of milk; Calculating the acidity of milk; Alkaline tablets; Acidity of cream . . ‘ . . CHAPTER VI CREAM Composition of cream ; Testing cream ; Methods of creaming ; Adulteration of cream ; Ripening of cream; The use of pure cultures; Influence of delay on the creaming of milk; Creaming of mixed milks; Cream raising by dilution . . : 5 . s . : . CHAPTER VII Tue CHEMISTRY OF BuTreER Maxine Churning ; Dairy salt; Buttermilk; Losses of fat in butter making ; Composition of butter; Butter colors; Over- runs ; Dividends; Judging butter . . . . . PAGE 35 43 50 62 CONTENTS CHAPTER VIII Tue Sanitary Conpition or MILK Unwholesome milk; Factors influencing the sanitary condi- tion of milk ; Condition of the animals as to health; Care of the animals ; Care of milk and dairy utensils ; Food and water which the animals receive; Colostrum milk ; Tyrotoxicon ; Fibrin in milk; Gases in milk; Keeping qualities of milk . 3 3 ‘ s < : 6 CHAPTER IX Tue Cuemistry or Currse MAKING Cheese making and butter making compared; Proteids in milk; Casein; Albumin; Rennet; The rennet test ; Process of cheddar cheese making; Process of stirred- curd cheese making; Distribution of milk solids in cheese making; Curing of cheese; The cheese yield of milk ; Testing cheese by the Babcock milk test ; Composition of cheese ; ‘esting whey ; Making out dividends in cheese factories; Comparative butter and cheese returns from milk ; Different kinds of cheese 7 7 a . . CHAPTER X Mi.k By-propucts Uses of by-products; Skim milk—composition, value, and use; Whey —composition, value, and use; Fertilizer value of milk by-products; Comparative value of skim milk compared with milk of other domestic animals : CHAPTER XI Tae ApULTERATION OF Darry Propucts Oleomargarine ; Simple methods for detecting oleomargarine ; Renovated butter; Adulteration of cheese ; Adulteration of milk; Other methods for testing milk ; Dairy laws PAGB 75 88 107 112 x CONTENTS CHAPTER XII Marxer Mix anp CREAM PAGE Variable character of market milk ; Changes in composition of milk during transportation; Pasteurizing milk and cream ; Condensed milk ; Milk as human food . - 119 CHAPTER XIII INFLUENCE OF DIFFERENT Foops UPON THE QUALITY or Mitk anp Dairy Propucts Food and milk secretion; Feeding fat; Production of hard butters ; Production of soft butters ; Effects of individual foods; Desirable flavors in milk products; Influence of balanced rations; Milk secretion . é ‘ F . 125 CHAPTER XIV Tur Rationaut Fesepine or Darry Stock Uses of food; Nutrients and their functions; Dry matter ; Ash; Organic matter; Proteids; Carbohydrates ; Crude fiber; Crude fat; Digestible nutrients; Caloric value or heat units of a ration; Nutritive ratio; Selection of foods for rations ; How to calculate a ration ; Compara- tive cost and value of grains. . : i » 131 APPENDIX Tables of composition of fodders and feeding stuffs ; Tables for correction of lactometer readings ; Review questions ; References . . . ° i F : ¥ . 147 InpExX . ; : ° é s : : ‘i é . 187 DAIRY CHEMISTRY DAIRY CHEMISTRY CHAPTER I THE COMPOSITION OF MILK 1. Complexity of Composition.— When milk is separated into its component parts, as water, fat, casein, albumin, sugar, and ash, the process is called analysis. While these are the principal compounds obtained when milk is analyzed, there are a num- ber of other substances present in smaller amounts which affect the quality of milk both for manufac- turing and food purposes. Milk is one of the vital fluids of the animal body and is necessarily of com- plex composition. 2. Milk Serum.— Of the various constituents of milk, the sugar, ash, and albumin are in solution, and in the fresh milk the casein is practically in a soluble form. The fat, however, is not in solution, but is in the form of minute globules suspended in the solution which contains the sugar, ash, albumin, and casein and which is known as the milk serum. The milk serum includes all of the constituents of the milk except the fat. The term “serum solids” is applied to those substances of milk which are dis- solved in the water, —the sugar, ash, albumin, and casein taken collectively. B 1 2 DAIRY CHEMISTRY 3. Milk Solids.— When milk is evaporated to dry- ness, the water is expelled and the milk solids are obtained. Milk solids are a mechanical mixture of fat, casein, albumin, milk sugar, and ash. Normal milk contains about 18 per cent of solid matter ; some samples contain as low as 12 and a few as high as 14 per cent. The amount of milk solids varies pro- portionally with the fat content of the milk, the higher the per cent of fat the larger the amount of solids. In the chemical analysis of milk, the solids are obtained by evaporating a weighed quantity of milk to dryness in a small dish which has previously been carefully weighed on a very delicate balance. The weight of the milk solids is then obtained and the percentage amounts calculated. EXAMPLE eee Weight of milk + dish 23.360 Weight of dish 12.850 Weight of milk 10.510 Weight of dish + solids 14.195 Weight of dish 12.850 Weight of milk solids 1.3845 10.51 : 1.845 ::100: a. 1.345 x 100 _ : cy; es 12.80 per cent solids. 100 — 12.80 = 87.20 per cent water. h i Fic. 1.— Determining the solids a : see cent of water in in milk. milk is obtained by subtract- THE COMPOSITION OF MILK 38 ing the per cent of solids from 100, as the loss in weight during evaporation is the water expelled as steam. There are rarely more than 88 pounds of water in 100 pounds of milk; average milk contains about 87 per cent, while some of the richest milks contain 86 per cent or less. The milk solids, unless obtained in a specially constructed water oven, are brown in color, due to slight charring of the sugar and other compounds. ‘The solids of milk are some- times termed dry matter und sometimes solid matter. They are composed of fat, casein, sugar, albumin, ash, and other compounds found in smaller amounts. 4. Milk Fats. — Average milk contains about 3.5 per cent of fat; some normal samples may contain 3 per cent or less, while others may contain 5 per cent or more. Fat is the most variable constitu- ent in milk. Cream contains ordinarily from 18 to 35 per cent of fat, and well-made butter about 85 per cent. For butter-making purposes the value of the milk is directly proportional to its fat content. Milk fat is mainly familiar as the product obtained by churning cream. Milk fat and commercial butter, however, are not synonymous terms. By milk fat is meant the pure dry fat, free from water, salt, or casein, while butter contains all of these materials in variable amounts. ‘The determination of the fat in milk by the Babcock test is discussed in the second chapter of this work, and the composition and properties of the fats are considered in other chapters. 4 DAIRY CHEMISTRY As previously stated, the fat in milk is not present in solution, but in suspension in the form of minute globules. These milk fat globules are about one five- thousandth of an inch in diameter. A cubic milli- meter of milk is estimated to contain from 2,000,000 to 4,000,000 fat globules, or a single drop from 100,000,000 to 150,000,000. Under the microscope the fat globules appear grouped together in small colonies. The size of the fat globules varies (1) with the breed and individuality of the animal, and (2) according to the length of time the animal has been in milk. When a cow is fresh, there is a smaller number of globules, but the globules are larger ; when the cow is well along in her milking period, the globules are smaller but more numerous. The milk from the Channel Island breeds is characterized by large fat globules, while the milk from the lowland breeds contains smaller globules. The fat globules must be massed together and collected when butter is made. The more completely they are recov- ered, the greater will be the amount of butter produced. The fat globules are simply solid masses of fat. At one time it was believed that they were cur- rounded by a membrane, and in churning it was supposed that the membrane had to be broken before the globules would mass. Recent chemical investi- gations have shown that there is no membrane sur- rounding the fat globules. The fat globules are lighter than any of the constituents of the milk PLATE. 1 JERSEY MILK FAT GLOBULES PLATE Il HOLSTEIN MILK FAT GLOBULES THE COMPOSITION OF MILK i] serum. ‘They retain their form and individuality on account of surface tension, which is the pressure that is exerted on the surface of the globules and is equal on all sides, hence the spherical form of the globules. 5. Casein. — Average milk contains about 3 per cent of casein, which in fresh milk is practically in a soluble condition, but in sour milk is precipitated as curd. The per cent of casein in milk is quite con- stant, ranging from 2.8 to 8.5 per cent. As ageneral rule, normal milk contains less casein than fat. In a pure state casein is a grayish white powder. Casein takes a very important part in cheese making and other dairy operations. Its chemical and physi- cal properties and the changes which it undergoes will be considered in other chapters. 6. Albumin. — Average milk contains about one half of one per cent of albumin, which is nearly iden- tical with egg albumin, or the “white” of the egg. Albumin and casein have about the same general composition, but different properties; they belong to the class of bodies called proteids, and are very complex in composition, differing from fat and sugar by containing the element nitrogen, which is not found in the fats and sugars. When fresh milk is boiled, the coagulum which forms on the surface is albumin. The amount of albumin in milk is quite constant and ranges from one half to three quarters of a per cent. 7. Milk Sugar. — Lactose, or milk sugar, is present in milk to the extent of about 5 per cent. When 6 DAIRY CHEMISTRY obtained in the pure state, it resembles in appearance confectionery sugar, but not in taste. Milk sugar takes an important part indirectly in butter and cheese making, as it is the material from which the acid is formed that sours the milk. The amount of milk sugar or lactose in milk is quite constant, ranging from 4.6 to 5.4 per cent. In average milk it is the constituent which is present in the larg- est amount of any of the milk solids. The part which milk sugar takes in butter and cheese mak- ing will be considered in other chapters of this work. 8. Ash. — When the milk solids are burned, there is a small amount of grayish white ash obtained. The ash content of milk is constant and varies but little from three quarters of one per cent. Milk ash is composed of common salt, and phosphates and chlorids of potassium, calcium, and magnesium, to- gether with small amounts of other minerals. A portion of the phosphorus is in combination with the casein. When milk is analyzed in the laboratory, the ash is obtained by completely burning the milk solids at a low temperature. The small dish containing the milk solids (see section 3) is placed either over a specially regulated flame or in a low-temperature muffle furnace to completely burn the sugar, casein, albumin, and fat without volatilizing any of the mineral salts. The dish containing the milk ash is then weighed and the per cent of ash determined. THE COMPOSITION OF MILK 7 EXAMPLE Milk taken 10.51 gm. See section 3. Grams Dish and milk ash 12.928 Dish 12.850 Ash 0.078 LES 10.51: .078::100: a. O78 x 100 ager .74 per cent ash. 9. Variations in Com- position of Milk.— A ver- age milk has about the , as following general com- Fis. 2. — Determining the ash in position : — = PER CENT Thance, Per cent Weater 5. is) Me) aha bags 6 87.00 89.6 to S24 Fats ose Gre Ge eS 3.50 2.5 to 6.0 CaS@ly x se SOOKE A eae “S 3.20 2.5 to 4.0 Albumin « 4 6% 8 8 « « 0.50 0.5 to 0.8 Milk Sugar . 2... ... 5.00 4.3 to 6.0 Ash: % ® 4 a & % 4 % 0.75 0.6 to 0.8 Solids 13.00 10.4 17.6 It is seldom that the extreme limits as given for the composition of milk are met with; occasionally an individual animal may give milk of abnormally high or low solids and fat, but it is rarely the case that the milk from an entire herd will contain either the 8 DAIRY CHEMISTRY maximum or the minimum percentage of milk solids. Milk varies in composition with the individuality of the animal, period of lactation, care, exhaustive- ness of milking, general condition as to health, and nature of the food consumed. Individuality, as breed characteristics, influences the composition of milk to a greater extent than the other factors enumerated. The extent to which some of these factors influence the composition of milk will be discussed in other chapters of this work. As an example of the composition of milk from different breeds, the following table taken from the New York Experiment Station, and representing one year’s work, is given : — To’ Brees Bonne. | petite | eee, | Svome | pak PER CENT Per cent | *® Holstein-Fresian | 12.39 3.46 3.89 4.84 0.74 Ayrshire 13.06 3.57 3.43 5.33 0.70 Jersey 15.40 5.61 3.91 5.15 0.74 Am. Holderness | 12.63 3.55 3.39 5.01 0.70 Guernsey 14.60 5.12 3.61 5.11 0.75 Devon 18.77 4.15 3.76 5.07 0.76 While these figures do not necessarily hold true for all herds, or for individual animals of any breed, they show the average composition of the milk for an entire season from a number of representative animals of different breeds. In determining the THE COMPOSITION OF MILK 9 value of milk for butter or cheese making purposes, the yield in pounds as well as the percentage compo- sition of the milk must be considered, as it frequently happens that the cows giving the richest milk also give the smallest yield of milk. 10. Percentage Composition and Total Yields. — In order to determine the total yield in pounds of each constituent produced by a cow or by a herd for a given period, the total weight of milk is multiplied by the percentage composition. In case it is desired to compare the yields of milk solids of two cows, giving respectively a total of 110 and 140 pounds of milk in three days, an analysis would have to be made of each milk. Suppose the milks give the following results upon analysis : — Composition OF MILK aN pes oe nhs Milk solids. . 2. 2. 2... 13.14 12.56 Milk fats . . . fae gl gt UG 4.06 3.26 Casein and sib, Sr Se, eet 3.34 3.54 Ashe ae ey) eae! wk 2) Ge “ed 0.70 0.72 SUPAP se ae eee SS 5.04 5.04 ToraL YIELD oF MILK SoLips Cow No.1 Cow No. 2 Milk fats, 110 x .0406= 4.47 140 x .0326= 4.56 Casein, 110 x .03834= 3.67 140 x .0354= 4.95 Ash, 110 x .007 = 0.77 140 x .0072= 1.01 Sugar, 110 x .0504= 5.54 140 x .050£= 7.06 Total 14.45 17.58 10 DAIRY CHEMISTRY While the difference in percentage composition of the milk is .8 of a per cent of fat in favor of cow No. 1, the total yield of fat for three days is .1 of % pound in favor of cow No. 2. Cow No. 2, how- ever, produced a larger amount of milk solids in the form of fat than cow No. 1. In general it is to be noted that whenever a cow produces a pound of butter fat, she also produces about 1.1 of milk sugar, about a pound of casein and albumin, and about .15 of a pound of ash. When milk is paid for on the basis of its fat content for butter making purposes, the total pounds of fat are obtained by multiplying the weight of the milk by its per cent of fat, as 287 pounds of milk testing 8.6 per cent fat contain (287 x .036) 10.383 pounds of fat. In dairy operations all comparisons and calculations are made on the basis of the total fat. ll. First or Fore Milk and Strippings. — As is well known, the first portion of milk given by any cow at a milking is poor in fat, while the last portion, or strippings, is very rich in fat. The per centage amounts of casein, ash, and sugar, and other ingredients, however, remain nearly constant. The difference in fat content between the first or fore milk and the strippings suggests the impor- tance of careful and exhaustive milking, and also thorough mixing of the milk before taking a sample for analysis. The composition of the first pint and the last pint of milk from two cows is given ag an illustration. THE COMPOSITION OF MILK 11 Cow No.1 Cow No. 2 First pint | Last pint | First pint | Last pint per cent per cent per cent per cent Total solids... . . 9.42 19.49 10.10 18.47 Batis: « . « @ & ws 0.71 1O.8¢ 1.02 9.49 Solids, not fat . . . . 8.71 8.65 9.08 8.98 Ash «¢ «© « @ & © % 0.68 0.72 0.70 0.74 Casein, albumin .. . 3.44 3.51 3.35 3.65 12. Milk Serum, Constancy of its Composition. — The solids of the milk serum are fairly constant in composition. This is well illustrated in the example u vie Milk Water Fat Casein MilkSugar Allumin Hdh Fic. 3.— Average composition of milk. given of the composition of first or fore milk and strippings. The solids of the milk serum, also known as the solids not fat, are never less than 8.25 per cent and rarely more than 9.75 per cent. The 12 DAIRY CHEMISTRY average is about 9 percent. The greatest difference in the composition of various milks is in the fat con- tent. Any material increase in the total solid mat- ter of milk is due mainly to an increase of the fat. The solids not fat are subject to but slight varia- tions compared with the fluctuations of the fat. Nearly all of the important fluids of the body, like the blood, are normally quite constant in chemical composition. With milk the constancy of composi- tion is confined mainly to the serum solids, or solids not fat. CHAPTER II MILK TESTING 13. Importance of Milk Testing. —A knowledge of the fat content of milk is essential in order to determine (1) any unnecessary waste in the manu- facture of butter and cheese, (2) the value of indi- vidual cows, (8) the cost of producing milk, (4) the value of different fodders and grains for milk-pro- ducing purposes, and (5) the commercial value of milk. A number of simple methods have been proposed for testing milk; some of them require a more extended knowledge of chemical operations than others. The method which is in most general use on account of its accuracy, simplicity, and cheapness is the Babcock centrifugal method. 14. Reliability of the Babcock Test. — This method has been tested by many chemists, and in all cases it has been found to give reliable results. There is a tendency, however, to read the fat percentages too low. This will be considered more in detail in dis- cussing that part of the operation. In the case of skim milk and buttermilk, when the fat is present to the extent of only two tenths of a per cent or less, the method may not give absolute results. This 13 14 DAIRY CHEMISTRY does not impair the usefulness of the test, because frequently the losses in skim milk and buttermilk are greater than this, and so far as the whole milk is concerned the method is perfectly reliable. When the Babcock test shows only a trace of fat ia the skim milk or buttermilk, the losses are very small. 15. Sampling Milk. — Milk should be thoroughly mixed before sampling. The milk as it comes from the cow or when it Las been standing is not in a condition to sample until it has been thoroughly mixed, either by pouring from one pail to another or by stirring with a long-handled dipper. Milk brought to the creamery in cans also requires thor- ough mixing before sampling. This is best accom- plished by the use of a long-handled dipper. Before sampling, the milk should be weighed. The milk should not be measured into the test bottles when it is either hot or cold. At a kigh temperature the milk is expanded and may contain an abnormal amount of dissolved air; while at a low temperature the milk may be unduly contracted. A temperature of 70° to 80° is the most suitable for measuring milk. If the milk has been standing for some time in the sample bottle, it is necessary to mix it thoroughly before measuring with the pipette. To do this, turn the milk from the sample bottle into another bottle or dish, pouring it down the side to prevent the formation of foam. In case the sample bottle has been standing until the fat has separated into a layer of cream, the bottle may be placed in a MILK TESTING 15 bath of warm water, temperature 100°, to liquefy the fat before mixing. Milk which shows the pres- ence of clots of cream or small particles of butter formed during the shak- ing of the sample bottle is not in condition to be measured with the pipette. If the sam- pling of the milk has not been carefully done, the work of testing isof little value, as the sample taken fails to represent the milk tested. 16. Measuring Milk with the Pipette. — The apparatus used for meas- uring the milk is called a pipette (see Fig.4). In order to fill the pipette put the pointed end into the milk, apply suction with the mouth until the milk rises just above the point @ on the stem ; then close the end with the index finger of the 176 CC. Fic. 4.— Measuring milk with the pipette. right hand, holding the pipette in the way shown 16 DAIRY CHEMISTRY in the cut. Thesecond and third fingers are opposite the thumb, while the little finger rests against the stem. When held in this way, the pipette is pre- vented by the little finger from swaying sidewise ; while the thumb, with the second and third fingers on the opposite sides, secures a good hold and leaves the index finger free to properly control the flow of milk from the pipette, and thus rapid measurements can be made. If the pipette is wet, rinse it with a little of the milk before using it. In passing from one milk to another, clean the pipette by rinsing it with the milk that is to be tested. The pipette should be thoroughly cleaned, first with cold water, then with hot water at the close of the work. The pipette holds 17.6 cc. of water, and delivers 18 gm. of milk. Hold the test bottle in the left hand at an angle of about 60°. Let the tip of the pipette if large just touch the inside of the neck of the test bottle, in order to permit air to pass out of the test bottle, otherwise the milk will spatter. Allow plenty of time for the pipette to drain; remove the last few drops by blowing. 17. Making the Test. — The test bottle (see Fig. 5) is provided with a neck which has a graduated scale from 1 to 10. Each larger division is divided into five smaller divisions, each representing .2 of a per cent of fat. The test bottle is usually provided with a copper collar bearing a number. Fill the acid measure, Fig. 6, up to the 17.6 cc. mark with sulphuric acid. The action of the sulphuric acid MILK TESTING 17 will be considered in another paragraph. Pour the sulphuric acid from the acid measure into the test bot- tle which contains the milk. The acid and the milk ES should be of nearly the same tempera- i ture, 70° F. By While the acid 2 is poured in, ro- Ls tate the test bot- 4 tle so as to wash E all of the milk down from the stem. After the acid is added, take the bottle by the stem and mix the acid and the milk by rotating. The solution be- comes a dark cof- fee color, due to Fic. 5.— Milk test the acid charring bottle. the sugar. The acid first precipitates the casein and then dissolves it. The acid does not act on the fat. The fat is separated from the milk serum by cen- trifugal action. There are a number of different kinds and sizes of centrifugal machines, but they all act on the same principle. The test bottles are placed in the pockets of the centrifugal machine. Cc Fic. 6.— Acid measure. 18 DAIRY CHEMISTRY In case there are not enough bottles to fill the machine, arrange the bottles so there will be an even number on each side. If this is not done, the machine is unbalanced, and the bearings will soon become badly worn. The bottles are to be whirled five minutes at the rate of 900 revolutions per minute. Directions for speeding the machine will be found in another paragraph. The start- ing and stopping of the machine should be done gradually. After whirling five minutes, the test bottles are to be filled with hot water up to about the eighth mark on the stem. The air bubbles which are sometimes caught in the neck should be allowed to escape. The bottles are then whirled two minutes longer in order to collect all of the fat in the graduated stem. In using the machine always put on the cover so as to prevent any accident. None of the apparatus used in this test is patented, and a good homemade centrifugal machine will answer every purpose. The bottles and other glassware can be purchased separately. 18. Reading the Fat.— When the test is completed, the fat in the stem of the test bottle presents the appearance shown in Fig. 7. Read from the low- est point 6 to the highest point a. Each large divi- sion, as 1 to 2, represents a whole per cent of fat; each of the smaller divisions one fifth or two tenths of a per cent. Suppose the top registers seven large divisions, and three small, then a =7.6. If 8 registers MILK TESTING 19 two large and three small divisions, 6 = 2.6. 7.6 — 2.6 = 5.0, the per cent of fat in the milk. Do not read from other points than a and 4, other- wise the results will be too low. The bottles are made to read in just this way. The reading should be done before the fat cools and streaks down the sides. In case a num- ber of readings Y ecnaia loo HHDIMNS are to be made, 4 the test bottles I 5 should be set in Seb a pan of hot re water, or hot are water can be Lo run into the pan of the machine, to prevent the LA bottles team Fia. 7.— Reading the test. cooling. Dividers can be used as indicated in the figure, but should be spread from 0 to 5. 19. Calibration of Test Bottles. — All test bottles should be rejected when inaccuracy of the divisions can be detected with the eve. In the most careful work they should be calibrated with mercury: 27.18 gm. of clean metallic mercury should just fill the 20 DAIRY CHEMISTRY space between the 0 and the 10 in the scale. Each small division is equal to .04 cc., or, as usually made, about one and one half millimeters. The test bottles can also be calibrated with water in the following way: The bottles are filled with pure distilled water up to the 0 mark, and then from an accurately graduated burette, graduated to 4, cc., water is added. It should require 2 cc. of water to fill the test bottle from the 0 to the 10 mark. For ordinary work the bottles can all be tested with one sample of milk, and all bottles rejected that show a greater difference than one small division. Accurately gradu- ated test bottles can usually be obtained from supply houses that deal in chemical apparatus. Inaccu- rately graduated test bottles are occasionally the cause of much trouble and dissatisfaction in the creamery. 20. Speeding the Machine. — A centrifugal of 14 inches’ diameter should make about 900 revolutions Fic. 8.— Centrifugal machine. per minute. In order to speed the machine count the number of revolutions that the test bottles make MILK TESTING 21 for every revolution of the crank wheel. Suppose the test bottles make 12 revolutions while the crank makes one. In order that the bottles may make 900 revolutions per minute, the crank must be turned 75 times in a minute (900 + 12= 75). In case the machine is less than 14 inches in diameter a greater number of revolutions is necessary. DiaMerer of CentrirugaL, IncuEs NomsBer or REVOLUTIONS PER MINUTE 10 1050 12 975 14 900 16 850 18 800 20 750 21. Centrifugal Action. — As previously stated, the fats are lighter than the milk serum, and when the milk is whirled in the test bottles, there is a separation of milk fats (lighter particles) from the milk serum (heavier portion). The serum goes to the outside of the circle of revolution, while the fats mass in the center, where they are finally collected in the gradu- ated stem of the test bottle. The sulphuric acid, which is one and eight tenths heavier than water, also aids in the separation both by increasing the specific gravity of the milk serum and by chemical action upon the albumin and casein. The cream separator works on this same principle. In the case of the separator, provision is made for the escape of the fat into a tube as it collects at the center. Cen- trifugal action is well illustrated by whirlpools, where 22 DAIRY CHEMISTRY all of the foam and light material, as leaves, collect in the center. 22. The Acid. —Commercial sulphuric acid (sp. gr. 1.82), about 90 per cent strength, is used. One pound of acid will make about twenty tests. When the acid is too strong, the fat presents a blackened and charred appearance; if too weak, par- ticles of undissolved casein appear immediately below the fat line. When just right, the fat sepa- rates in a distinct and well-defined layer and looks like butter. If the acid is too strong, and chars the fat, use a smaller amount in making the test. In that case, if the test is not satisfactory, the acid should be exchanged for a new lot. Do not attempt to dilute the acid with water. If the acid is too weak, a larger amount than 17.6 cc. may give satis- factory results. The strength of the acid can be determined by using a hydrometer for heavy liquids, and noting the depth to which the spindle sinks in the acid. To obtain the best results, the acid should vary but little from 1.82 specific gravity or 90 per cent strength. Strenetu or Ao SproIFic GRaviTy 88 1.808 89 1.815 90 1.820 91 1.825 92 1.830 93 1.834 94 1.837 95 1.839 MILK TESTING 23 The acid as well as the washings and contents of the test bottles can be handled only in glass or earthen- ware. The acid should never come in contact with tin or a metallic dish of any kind. If acid is spilled on the floor or desks, wash it up imme- diately, using plenty of water. If a large quantity is spilled, ab- sorb it with sawdust, bran, or fine clay. In case any is spilled on the clothing, rinse with water and then apply ammonia to the spots. Never throw the acid waste near a tree or where a person or ani- mal is obliged to walk. A convenient form of apparatus for meas- uring the acid where a large number of tests are to be made is shown in Fig. 9. @ is the acid bottle connected Fig. 9.— Acid measuring apparatus. with glass tube 6d to a pipette. The stopcock f can be turned so as to allow the acid to run into the test 24 DAIRY CHEMISTRY bottle g. The automatic pipette is fastened to an iron stand dd, which rests upon the table. Other forms of apparatus are also in use. In ordinary practice a strong glass vessel with a good lip for pouring is the most satisfactory arrangement for handling the acid. A white tile is excellent to have on the table under the acid bottle. 23. Composite Sample. — In actual creamery prac- tice the daily testing of each patron’s milk, or in the dairy, the testing of both morning’s and evening’s milk from each cow is too expensive. To obviate this daily testing, a composite or compound sample is made up by saving a small sample of each milk in a pint fruit can. At the end of one week or of two weeks the compound sample is carefully mixed and tested. Inasmuch as this test represents a propor- tional part of each lot of milk, it gives the average amount of fat in the milk for the period. In cream- eries and factories, where milk is paid for by test, the composite test when properly carried out gives good results. The composite sample should be kept covered so that the surface of the cream will not become dry and leathery. The sample should also be kept ina cool place to prevent fermentation. Various chemicals are used to keep the milk fresh. Potassium bichromate has been found to give the best satisfaction. About one half gram of potassium bichromate will be sufficient to preserve a pint of milk. Winton and Ogden state that a .22 pistol MILK TESTING 25 shell cut one-half inch long will hold, loosely filled, approximately one-half gram of bichromate. For convenience in handling the shell can be soldered to a piece of stout wire. Put the bichromate in the sam- ple cans when empty, and no more need be added until a new composite sample is started. The bichromate imparts its characteristic yellow color to the milk. In case corrosive sublimate or any other poisonous material is used for preserving the composite sample, it is best to color the milk with aniline so as to pre- vent accidental poisoning from use of the milk. Small four or six ounce, wide-mouthed bottles may be used for holding the composite samples. Bottles with glass stoppers are the best. Rubber stoppers may be used, but cork stoppers should never be used. They are difficult to clean, and they cause the milk to sour. When the composite sample becomes “lumpy” and is difficult to sample, a very small (.1 gm.) piece of caustic potash may be added before mixing the milk. The potash will dissolve the lumps of curd. A few drops more than 17.6 ec. of acid should then be used. When only a small number of tests are to be made, the following plan may be followed: Save about two ounces of each milk separately in glass bottles or cans; at the next milking add a proportional quan- tity. A composite sample of the day’s milk is thus obtained, and while still fresh is mixed, and then by means of a small pipette, 5.9 cc. are measured into a test bottle twice the size of those ordinarily used, or test bottles made for 35 cc. of milk. In a similar 26 DAIRY CHEMISTRY way the milk for six days may thus be measured directly into the test bottles, and then tested. 24. Testing Skim Milk. — In testing skim milk the special test bottle devised by Farrington, with the - small neck and the side tube for the addition of the acid, should be used (see Fig. 10). Each division on the neck represents .05 of a per cent. In using these bottles, it must be remembered that the small amount of fat ob- tained in the neck is not neces- sarily all of the fat in the skim milk, because some of it may be present in such a fine state of divi- sion that it is not brought up into the neck. Hence the results are usually slightly lower than those obtained by chemical analysis. This, however, does not seriously impair the test. When the test shows only a trace of fat, the Frc. 10.—Skim milk test butter maker can feel satisfied that aie he is doing good work. 25. Sampling Frozen Milk.— When a can of milk freezes, the ice forms on the outside and there is usually a central part that does not freeze. The un- frozen part is richer in fat and solids than the frozen part. The ice in the center of a can is richer in milk solids than the ice of the outer portions. When {1 trererrrrt MILK TESTING 27 frozen or partially frozen, milk is not in a condition to sample, but should be allowed to thaw and then be thoroughly mixed. 26. Cleaning Glassware. —JIn order to secure the best results, the test bottles and all of the glassware used in testing milk should be kept clean. The test bottles should be emptied before the fat becomes cold and hard. By shaking the test bottle, the sedi- ment of lime sulphate or gypsum is removed with the acid mixture. The test bottles can be left to drain on the drain board placed over the acid waste jar. A drain board with holes large enough to receive the neck of the test bottle will be found very useful in handling a large number of test bottles. The test bottles should be rinsed while still hot with warm water and after draining this should be followed by a second rinsing with hot water. 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