Modern methods of testing milk and milk products; a handbook prepared for the use of dairy students, butter makers, cheese makers, producers of milk, operators in condenseries, managers of milk-shipping stations, milk inspectors, physicians, etc

Front matter

B()ok_^LL

CopjTiglil N"-

COl'YRlCliT DKPOSIT.

Preface

To attain the highest degree of success in the production of milk and in the manufacture of its products, it has become essential to acquire some knowledge of the methods of testing milk and milk products. The application of these methods to dairying has resulted in lifting the dairy industry to a higher plane of intelligence, and in effecting changes of great •economic importance, among which may be briefly mentioned: (i) Greater justice rendered milk producers in paying for milk according to its quality. (2) Prevention of large losses, once very common, in the manufacture of butter and cheese. (3) Improvement of methods of manufacture through better control of details. (4) Increase of yield of products made from a given amount of milk. (5) Improvement in the uniformity and quality of manufactured dairy products.

This little book has been prepared for the use of dairy students, cheese-makers, butter-makers, producers of milk, operators in condenseries, managers of shipping-stations, milk-inspectors, and others interested. Physicians who are specialists in infant- feeding will find the book useful in testing human milk as well as cows' milk that is modified or to be modified.

No previous chemical training is required for operating successfully the methods described. Any intelligent person who can labor with painstaking patience and appreciate the value of attention to little details should be able to master these methods with a rea-

VI PREFACE

sonable amount of work. The assistance of a trained teacher will, of course, make the task easier. No one, whatever his educational preparation, can hope to use these or any similar methods successfully who can not or will not follow instructions accurately and exercise patience in mastering every minute detail.

In the preparation of this work, the writer has tried to keep in mind the following points : ( i ) Accuracy, simplicity and clearness of statement. (2) Making prominent, as far as practicable, the reasons for each step in each process. (3) Emphasis of common difficulties and instructions for overcoming them. (4) Impressing students with the necessity of precision and care in performing ever}^ detail given. (5) Selection of the methods approved by experience. (6) Avoidance of such technical methods as require unusual skill or equipment. (7) Omission of unnecessary details. (8) Embodiment of the results of the most recent investigations. (9) The special needs of those for whose use the work is designed.

The scope of this work is far from exhaustive, but the methods selected are given with necessary completeness. Chemical methods, requiring elaborate equipment and extended special training, are purposely omitted. Any one desiring a full description of such methods can obtain it by addressing a request to the U. S. Department of Agriculture, Bureau of Chemistry, Washington, D. C, asking for a copy of "Methods of Analysis adopted by the Association of Official Agricultural Chemists."

The methods that have been compiled here are in large measure the direct result of the work of our

PREFACE Vll

agricultural experiment stations, and afford some indication of the direction and value of the work done by these institutions.

In the preparation of Chapter XIV, valuable assistance has been kindly rendered by Mr. George A. Smith, Dairy Expert of this station.

L. L. Van Slyke.

New York Agricultural Experiment Station, 1906.

Contents

I

Chemistry of Cows' Milk and Milk Products . . 1

II III The Babcock Test — Description of Apparatus and

Materials 32

IV Method of Operating the Babcock Test . . ' . . 53

V

Method of Testing Cream by the Babcock Test . . 69

VI Methods of Testing Skim-milk, Whey, Butter, Cheese,

etc., by the Babcock Test 78

VII Methods "of Testing Acidity of Milk and Milk Products 88

VIII Methods of Testing the Bacterial Condition of Milk 105

IX Methods of Testing Milk by Rennet-Extract and

Pepsin 113

X Methods of Testing Specific Gravity and Solids of

Milk by the Lactometer 119

ix

X CONTENTS

XI

Methods of Testing Milk and Milk Products for Adulterations 133

XII

The Babcock Test applied to Farm Conditions . . 143

XIII Methods of Commercial Testing and Scoring of Butter and Cheese 150

XIV Methods of Commercial Testing and Scoring of Milk

and Cream 174

XV

ILLUSTRATIONS

PAGE

The Original Babcock Tester ..... Frontispiece

Composite-Sample Jars 25

Rack for Composite Samples 26

Sampling-Dipper 27

Scovell Milk-Sampler 27

Equity Milk-Sampler 27

Milk-Testing Bottle ............ 34

Milk-Measuring Pipette 35

Greiner's Automatic Pipette ....... 36

Wagner's Pipette 26

Acid-Measure 36

Acid-Burette and Stand 37

Automatic Burette ^., . . . 37

Steam-Turbine Tester . 38

Hand-Tester 38

Small Hand-Tester 39

Electric Centrifuge 40

Hydrometer for Testing Strength of Sulphuric Acid 43

Milk-Bottle Tester 46

Testing Accuracy of Milk-Bottle ....... 46

Burette and Support 48

Waste-Jar for Emptying Test-Bottles 50

Test-Bottle Rinser 50

Test-Bottle Draining Rack 51

Farrington's Bottle-Cleaner — Bottle-Holder Empty . 51

xi

Xll ILLUSTRATIONS

Farrington's Bottle-Cleaner — Bottle-Holder Immersed 52

Farrington's Bottle-Cleaner — Bottle-Holder Draining 52

Correct Way of Holding Pipette and Bottle ... 55

Wrong Way of Holding Pipette and Bottle ... 56

Measuring Fat-Column . 63

Automatic Russian Pipette 67

Russian Test-Bottle 67

Bulb-Necked Cream-Bottle 70

Straight-Necked Cream-Bottle 71

Cream-Testing Scales 72

Cream-Sampling Sieve 74

Bottles for Testing Skim-Milk 79

Glass Funnel for Use in Testing Butter .... 83

Mann's Acid Test 93

Farrington's Alkaline-Tablet Test . 96

Spillman's Acid-Cylinder 97

Purdue Alkali-Test 99

Hand-Centrifuge for Sedimentation Work . . . 110

Tube for Sedimentation Work 110

Bausch & Lomb Electric Centrifuge 110

International Instrument Co.'s Electric Centrifuge . Ill

Glass for Collecting Sediment in Milk 112

Monrad Rennet-Test 113

Marschall Rennet-Test 115

Quevenne Lactometer 122

Cylinder for Lactometer 125

Comparison of Different Specific Gravity Scales . . 126

Richmond's Slide-Rule 130

Butter-Trier 151

Modern Methods of Testing Milk and Milk- Products

CHAPTER I Chemistry of Cows' Milk and Milk Products

The normal milk of cows contains the following compounds and classes of compounds :

(i) Water. (4) Milk-sugar.

(2) Fat. (5) Salts or ash.

(3) Nitrogen compounds or proteids. (6) Gases.

WATER

The water present in milk, however much its presence may be disguised, is the compound of hydrogen and oxygen with which we are everywhere familiar. The water in milk serves the purpose of holding in solution the soluble constituents of the milk, and it also acts as a diluent, better fitting the mixture for animal nutrition.

Variation. — The amount of water normally contained in milk varies, depending upon such conditions as individuality, breed, stage of lactation, age, character of food, amount of water drunk, state of health, etc. In the case of single milkings of individual cows, the water may vary from 82 to 90 per cent, or more. In the case of milk from herds of cows, the water varies less, usually ranging from 86 to 88 per cent.

The influence of breed. — The following figures, from the records of the N. Y. Agricultural Experiment Station at Geneva, illustrate the influence of breed upon the water content of milk :

NAME OF BREED

Holstein Friesian .

American Holderness

Ayrshire . .

Short Horn

Devon

Guernsey

Jersey

Per cent, of ■water in milk

88.20

87-35

87.25

85.70

85-50

85.10 -

84.60

The influence of lactation. — The variation of water in milk, as affected by advance of the lactation period, is illustrated by the following figures, which cover a period of ten months from the time of calving:

Per cent, of

MONTH OF LACTATION watcr in milk

2 86.50

3 86.53

4 86.36

5 • . . . 86.25

6 86.00

7 85.82

8 : 85.67

9 85.54

10 85.17

There is noticeable a general tendency for the amount of water in milk to increase after the first three months of lactation, after which there is a continuous decrease to the end of the lactation period.

Total solids. — Under the general term of total solids or milk-solids, we indicate the constituents of the milk other than water (and gases). The per cent, of water in milk subtracted from loo gives the percentage of milk-solids, which include fat, proteids, milk-sugar and salts or ash. The amount of solids in milk varies with the same conditions that affect the percentage of water in milk, but, of course, in just the reverse manner. Most states orescribe a legal standard for milk-solids, usually 12 per cent., and milk containing less than the legal amount is regarded as adulterated.

MILK-FAT

The composition of milk-fat. — Milk-fat, also called butter-fat, is not a single chemical compound, but is a somewhat variable mixture of several different compounds called glycerides. Each glyceride is formed by the chemical union of glycerin as a base with some acid or acids of a particular kind. These glycerin-acid compounds, or glycerides, of milk-fat contain about ten different acids, some being present in small proportions. The four following acids enter most largely into the composition of milk-fat, in the form of their combinations with glycerin: Palmitic acid, oleic acid, myristic acid and butyric acid. The compounds, or glycerides, formed by the combination of glycerin and the acids, have special names derived from the acids; thus, we have palmitin (glycerin combined with palmitic acid), butyrin (glycerin combined with butyric acid), olein, etc. Milk- fat contains, on an average, about 40 per cent, of palmitin, 34 per cent, of olein, 10 per cent, of myristin, 6 per cent, of butyrin, and from less than i to nearly 3 per cent, of each of the glycerides of other acids. Milk-fat contains about 12.5 per cent, of glycerin in combination with the acids. The proportions of these constituents of milk-fat vary somewhat, and this variation influences the character of the milk-fat. Thus, palmitin and myristin tend to make milk- fat harder, while olein and butyrin have the opposite tendency.

The acids contained in milk-fat or butter-fat may be divided into two groups : ( i ) The acids in one group (palmitic, oleic, myristic, stearic, lauric) are insoluble in water and non- volatile, while (2) the other acids (butyric, caproic, etc.,) are more or less completely soluble in water and are volatile. These differences afford a practical basis for distinguishing pure butter from artificial butter. Of the fat-acids contained in butter- fat, about 87.5 per cent, consists of the insoluble fat-acids, while in other forms of animal fat (beef- fat, lard, etc.,) the amount of these insoluble fat-acids is considerably greater. The amount of volatile fat-acids in milk- fat or butter- fat is much greater than in other forms of animal fat.

Fat-globules in milk. — Milk-fat is present in milk, not in solution, but suspended in the form of very small, transparent globules. Globules varying in size between one twenty-five hundredth and one fifteenthousandth of an inch in diameter are the ones most commonly present. The average size of fat-globules in milk is somewhat more than one ten-thousandth of an inch in diameter. The smaller globules are more numerous than the larger ones. In one drop of average milk there are more than one hundred million fat-globules. Skim-milk contains fewer and smaller globules than whole ' milk, while the reverse is true of cream. The large globules do not differ in composition from the small ones. -The size and number of fat-globules in milk are influenced by such conditions as advance of lactation, breed of cow, food, age, health, different milkings, different parts of the same milking, etc.

It was formerly believed generally, and is still by some, that the fat-globules of milk are surrounded by a membranous covering, or else by a semi-liquid, albuminous layer. We may, however, accept it as established beyond reasonable doubt that the fat-globules of milk have no special covering of any kind, but are simply minute particles of fat floating free in milk in the form of an emulsion. Fat-globules quite generally retain their individuality even in butter and cheese.

Amount of fat in milk. — Normal milk varies greatly in its fat content, containing from below 2 to over 10 per cent., if we consider single milkings of individual cows. The milk from herds of cows varies in fat more commonly between the limits of 3 and 5 per cent. The average amount Of milk-fat in milk produced in this country, taking the true average for the entire year, lies somewhere near 4 per cent., perhaps a little under. Many of the conditions that affect the percentage of fat in milk are fairly well known, while others are little understood. We will briefly consider some of the well-recognized conditions that influence the fat content of milk.

(i) Infincnce of individuality of coiv on fat content of milk. — It is uncommon to find in a herd of

COWS t\yo individuals whose milk contains the same per cent, of fat, whether we consider single milkings or the average of many milkings.

(2) Iniincncc of breed of cow on fat content of milk. — It is well know^n that the per cent, of fat in milk varies in a somewhat characteristic way with the kind of breed of covv^. While there is marked variation in individuals of the same breed, there is found to be a fairly uniform difference, more or less marked, if we consider the averages of several individuals. It is largely owing to this influence that we find the milk of one country differing from that of another, or the milk of one section of a country differing from that of another section. For example, the average amount of fat in milk in Germany and Holland is fully one-half per cent, lower than in this country, because the prevailing breeds of cows there are those producing milk comparatively low in fat. The following figures, taken from the records of the New York (Geneva) Agricultural Experiment Station, represent averages of many individuals for several periods of lactation: Per cent, of

fat in milk NAME OF BREED Average Lowest Highest

Holstein Friesian 3.36 2.88 3.85

Ayrshire ....

American Holclerness Short Horn .

Devon

Guernsey ....

Jersey

444 4.60 5-30 5.60

3.20

(3) Influence of age of coiv on fat content of milk. — So far as published data throw light upon this point, there appears to be a tendency for milk to become less rich in fat with each succeeding period of lactation, especially after the second, though individual exceptions are not infrequent. More data are needed to settle the question definitely.

(4) Iniiiience of advance of lactation on the fat content of milk. — In general, it is found that the per cent, of fat in milk increases as the stage of lactation advances after the third month, as illustrated by the following data from the records of the New York (Geneva) Station, covering 10 months from the time of calving' :

NUMBER OF MONTH OF LACTATION I 2

4 5 6

Per cent, of fat in milk

4-54

4-33

4.28

4-79 5.00

(5) Variation of time between milkings in relation to the fat content of millz. — As a rule, the longer the time between two successive milkings, the smaller is the per cent, of fat in the milk; and the shorter the time between milkings, the greater the per cent, of fat. When the time between milkings is uniformly equal, the variation of fat in milk is small, provided the general environment of the animal is the same. However, as there are not commonly such entirely uniform conditions of surroundings during the day and night, there appears to be a common tendency for the presence of a Httle more fat in the morning's milk, even when milkings are apart the same length of time.

(6) Variation of fat content in different partialis of milk drazvn from the udder. — The following figures, taken from the writer's records, illustrate the general rule that the first milk drawn contains least fat, the milk last drawn (strippings) being the richest in fat:

Per cent, of fat in milk cow I cow 2 cow 3 First portion drawn .... 0.90 1.60 1.60 Second portion drawn . . . 2.60 3.20 3.25 Third portion drawn .... 5.35 4.10 5.00 Fourth portion drawn (strip'gs) 9.80 8.10 8.30

It is also known that the per cent, of fat in milk varies in different quarters of the udder of a cow, and also varies more or less in each quarter with the order in which the teats are milked.

THE NITROGEN COMPOUNDS OF MILK

Some confusion prevails in respect to the names of the nitrogen compounds of milk. They have been spoken of as albuminoids, proteids, etc. Frequently the word casein is erroneously used to include all the nitrogen compounds of milk.

How many nitrogen or proteid compounds are present in normal milk? What are they? Different workers have reported from one to seven or more. The chemical evidence at hand justifies us in the belief that fresh, normal milk contains not more than three or, perhaps, four nitrogen-containing or proteid bodies, viz., casein, albumin, globulin and galactase. Globulin and g-alactase are present in so small quantities that we can properly regard casein and albumin, quantitatively, as being essentially the nitrogen compounds of milk.

Milk-Casein is the most important nitrogen compound in milk, because, (ist) it is the one present in largest quantity; (2d) its presence makes it possible to convert milk into cheese; and (3d) it has a high value as food. Milk-casein is most familiar to us in the form of the solid, white substance called curd, which forms in milk when it sours (though, strictly speaking, this well-known, white substance is not milk-casein, but casein lactate).

(i) Composition of milk-casein. — Casein is a very complex chemical compound, containing the elements carbon, oxygen, hydrogen, nitrogen, sulphur, and phosphorus. In milk the proteid molecule of casein is combined with calcium, or some calcium compound, and hence the proper chemical name of milk-casein is calcium casein. It exists in milk, not in solution, but in the form of extremely minute, solid, gelatinous particles in suspension. The slime found in the bowl of centrifugal separators consists, to a considerable extent, of milk-casein.

(2) Action of acids npon milk-casein. — When milk sours in the ordinary way, the lactic acid formed acts upon the calcium casein, two chemical changes taking place. First, the lactic acid combines with the calcium of the calcium casein, forming calcium-free casein, or simply casein set free from its combination with calcium. When more lactic acid forms, the secend change takes place, the free casein combining directly with the acid, forming casein lactate, which is familiar as the curd of sour milk. Similar chemical changes occur when milk is treated with other acids, such as h3^drochloric, acetic, etc. Both free casein and its familiar salts formed with acids are insoluble in water. The action of acids on calcium casein and on free casein is hastened by increase of temperature. Both casein and casein compounds with acids dissolve in an excess of acid, probably forming soluble casein salts.

(3) Action of alkalis on milk-casein. — Dilute solutions of alkalis (caustic soda, ammonia, etc.) act upon casein and its salts with acids, forming compounds that dissolve easily in water. These alkali compounds of casein are not affected by rennet. Some of these compounds are found in commerce as food and medicinal preparations under such names as Plasmon, Nutrose, Santogene, Eucasein, Galactogene, etc.

(4) Action of heat on milk-casein. — Heat alone under ordinary conditions, even at the boiling point of water, does not coagulate the casein in milk. Casein may be coagulated by heating under pressure at a temperature of about 270° F. The browning of milk heated under pressure is more or less due to changes in the casein. The formation of a peculiar skin on the surface of milk heated above 140° F. is largely due to the calcium casein of the milk and not to albumin as was formerly supposed. The skin itself contains practically all of the constituents of the milk and may be regarded as a kind of evaporated milk.

(5) Action of rennet on milk-casein. — One of the most characteristic properties of the calcium casein

CHEMISTRY OF COWS MILK II

of milk is its coagulation by the enzym or chemical ferment contained in rennet, which is an extract of the mucous membrane of a calf's stomach. This property makes possible the manufacture of cheese from milk. The curd formed by the action of rennet is called paracasein or, more properly, calcium paracasein. There appears to be little or no chemical difference between calcium casein and calcium paracasein. The coagulation of calcium casein produced by rennet is quite different from that produced by acids. Calcium paracasein behaves towards acids and alkalis much like calcium casein.

(6) Other changes caused in milk-casein. — Under the action of chemical reagents, of enzyms and of various organisms, calcium casein and paracasein may be changed into a large number of other substances. Among the compounds and classes of compounds thus formed are paranuclein, albumoses, peptones, amides (crystallizable bodies) and ammonia. These products are never found in normal milk as it leaves the cow, but may be present in milk that has stood some time.

Milk-Albumin. — Milk-albumin differs from milk-casein in composition and behavior. Thus, milk-albumin (i) is not acted upon by rennet; (2) is not coagulated by acids at ordinary temperatures; (3) is coagulated by heat alone, though not completely, above 160° F. ; and (4) is in solution in milk.

Milk-Globulin. — This compound is present only in small quantities in normal milk and is of no special importance, so far as known.

Galactase. — This substance is an unorganized ferment, or a mixture of such ferments, present in normal milk. It somewhat resembles pepsin in its action, being able to coagulate milk-casein and then digest it or make it soluble. It is present in very small amounts in milk and its action is very slow. It has never been isolated from milk in pure form. It is probably a nitrogen-containing substance. Our knowledge of galactase is very far from complete.

Amounts of casein and albumin in milk. — In single milkings of individual cows, the casein and albumin, taken together, vary from 2.5 to 6 per cent, and average about 3.2 per cent. Milk-casein varies in amount from 2 to 4 per cent, and averages about 2.5 per cent. Albumin varies from 0.5 to 0.9 per cent, and averages about 0.7 per cent. The amount of casein in relation to albumin varies greatly. On an average, milk contains about 3.6 parts of casein for one of albumin, or, stated another way, casein constitutes about 80 per cent, of the nitrogen compounds of milk.

The amount of casein and albumin in milk is influenced by many conditions, such as influence the general composition of the milk, among which are individuality, breed, advance of lactation, etc. As the lactation period advances, there is a general tendency on the part of casein and albumin in milk to increase.

Relation of fat and nitrogen compounds in milk. — In normal milk containing over 3 per cent, of fat, the amount of casein and albumin is rarely greater than the amount of fat, especially in the milk of herds of cows. When the per cent, of fat is less than that of the nitrogen compounds, the milk may generally be regarded as skimmed, especially in the case of milk from herds.

MILK-SUGAR

Milk-sugar, also called lactose, Is present in cows' milk in solution. In general composition, it resembles ordinary sugar, but it is less sweet and less soluble in water. The amount of sugar in milk varies from below 4 to over 6 per cent, and averages about 5 per cent. Its importance in dairy work, especially in connection with the manufacture of butter and cheese, comes from the ease with which it is converted into lactic acid by certain forms of bacteria. In the ordinary souring of milk, the amount of milk-sugar decreases somewhat more than one-fourth and there is formed as a maximum about 0.9 per cent, of lactic acid. More acid may be formed after some time. Hence, sour milk, when two or three days old, contains only 3.5 to 4 per cent, of milk-sugar. The sugar of milk passes largely into the whey in cheese-making and forms over 70 per cent, of the solids in whey. The milk-sugar of commerce is usually prepared by evaporating whey and purifying the impure product first obtained.

THE SALTS OF MILK

The salts of milk, commonly included under the term "ash," are present in only small amounts, 0.7 per cent, on the average ; but they have important relations to milk and its products. Our knowledge of these compounds is very incomplete. The salts of milk are commonly spoken of as the ash or mineral constituents. This conception is somewhat misleading, because the materials appearing in the ash of milk are, to some considerable extent, combined in organic compounds, instead of existing in the milk as separate inorganic bodies. The ash represents in amount, therefore, more than the so-called mineral constituents of milk and less than the salts of milk. While the ash in milk amounts to about 0.7 per cent., the amount of salts probably approximates 0.9 per cent. A portion of the salts of milk is in solution, including such compounds as calcium citrate, sodium chloride, potassium acid phosphate, etc., while a portion (tricalcium phosphate) appears to be in suspension in the form of very finely divided particles.

THE GASES OF MILK

Milk contains more or less oxygen and nitrogen, these gases being carried into it mechanically from the air in the process of milking. It contains also, when freshly drawn, carbon dioxide, already present in the udder milk, there being probably between 3 and 4 per cent, by volume, a portion of which escapes at once while being drawn from the udder under usual conditions.

GENERAL SUMMARY

Milk contains water, fat, casein, albumin, sugar, salts, carbon dioxide and some other constituents in small quantities. The fat and casein and some of the salts are in suspension and not in solution, while albumin, sugar and the larger portion of the salts are held in solution by the water.

As a matter of convenience, the compounds of milk are divided into certain arbitrary groups. By one system of division, the compounds of milk are arranged in two classes: — (i) Water, and (2) inilksolids (or total solids), this second class including fat, casein, albumin, sugar, salts (ash), etc. Another division is made on the basis of the milk-fat into (i) fat and (2) milk-seriun, which includes all the milk constituents except the fat. Separator skim-milk is nearly pure milk-serum. Then we have the milk-solids subdivided into (i) fat and (2) solids-not-fat (casein, albumin, sugar, salts (ash), etc.)

The following arrangement shows the general relation of the compounds contained in milk, the figures indicating the percentages present in average milk:

Water

87.1

Fat 3.9

Solids^ Solids-not-fat

9.0 r Nitrogen compounds 3.2

j Milk-sugar 5.1 Ash (salts) 0,7 f Casein, I 2.5

I Albumin, etc. t 0.7

Carbon dioxide Gases -^ Nitrogen Oxygen

A^^RAGE ANALYSIS OF COWS MILK

WATER

TOTAL SOLIDS

FAT

CASEIN

ALBU- MIN

SUGAR

ASH

Average of 5,552 American analyses c o mpiled by the

Per cl. 87.1

87.4

12.6

3.75

Per ct.

2.5

2.45

Per ct.

0.7

0.7

5.0

0.7

Average cheese-factory milk for the season (May to Nov.) in N.Y. State...

i6

REPRESENTATIVE ANALYSES OF PRODUCTS AND BY-PRODUCTS OF MILK

TOTAL

ALBU-

WATER

SOLIDS

FAT

CASKIN

MIN

SUGAR

Per ct.

Per ct.

Per ct.

Per ct.

Per ct.

Per ct.

13.0

87.0

83.5

1.0

....

36.8

63.2

33.75

23.75 2

90.3

9.7

0.10

2.75 o.eo

5.25

93.4

6.6

0.35

0.10

0.75

4.80

90.6

9.4

0.13

2.80

0.80

4.40*

Butter.

Cheddar Cheese

(green) Skim-milk

(separator)

Whey

Buttermilk

5.73 0.80 0.60 0.70

1 Salt. 2 Paracasein. ^ Salt and Ash. * .60 per cent, lactic acid in addition.

DEFINITIONS AND STANDARDS OF MILK AND MILK PRODUCTS

The United States Department of Agriculture has estabHshed official standards for purity of dairy and Other food products, defining also what is meant by the terms used in designating different materials. These definitions and standards have been most carefully worked out by members of the Association of Official Agricultural Chemists, several years having been devoted to the collection of data. The official definitions and standards relating to milk and milk products are as follows :

MILK

Definitions. — i. Milk (ivholc milk) is the lacteal secretion obtained by the complete milking of one or more healthy cows, properly fed and kept, excluding that obtained within fifteen days before and five days after calving.

2. Blended milk is milk modified in its composition

SO as to have a definite and stated percentage of one or more of its constituents.

3. Skim-milk is milk from which a part or all of the cream has been removed.

4. Buttermilk is the product that remains when butter is removed from milk or cream in the process of churning.

5. Pasteurised milk is milk that has been heated below boiling but sufficiently to kill most of the active organisms present and immediately cooled to fifty degrees (50°) Fahr. or lower to retard the development of their spores.

6. Sterilised milk is milk that has been heated at the temperature of boiling water or higher for a length of time sufficient to kill all organisms present.

7. Condensed milk is milk from which a considerable portion of water has been evaporated.

8. Szveetened condensed milk is milk from which a considerable portion of water has been evaporated and to which sugar (sucrose) has been added.

9. Condensed skim-milk is skim-milk from which a considerable portion of water has been evaporated.

Standards. — i. Standard milk contains not less than twelve (12) per cent, of total solids, not less than eight and one-half (8.5) per cent, of solids-not-fat, and not less than three and one-quarter (3.25) per cent, of milk- fat.

2. Standard skim-milk contains not less than nine and one-quarter (9.25) per cent, of milk-solids.