Chapter 2

While the composition of milk has much to do with the quality of this food, it varies, as should be noted, in different breeds and even in individual cows, depending on both the food and the care given to them. For this reason, milk that is mixed is preferable to the milk of a single cow, as the mixing of the milk of a number of cows insures a better average composition.

23. ADULTERATION OF MILK.--The composition of milk, and hence its quality, is seriously affected by its adulteration. By this is meant the extraction of any of the food substances from whole milk; the addition of anything that tends to weaken or lower its quality or strength; the use of coloring matter to make it appear of greater value than it actually is; or the use of preservatives to prevent it from souring as soon as it ordinarily would. It is, of course, illegal to adulterate milk, yet it is sometimes done. The most convenient and possibly the most common materials used to adulterate milk are water and skim milk. The addition of water to milk decreases the quantity of all its food substances, but the addition of skim milk reduces the quantity of fat only. The color of the milk is often affected by the use of these adulterants, but when this happens, yellow coloring is usually added to restore the original appearance.

Sometimes the milk that a dairyman markets contains more fat than the law requires; but even such milk cannot legally be skimmed nor diluted with skim milk. The only thing that may be done to it is to mix it with milk that is low in butter fat and thus obtain a milk that will average the legal percentage. For instance, if milk from a dairy averages 5 per cent, of butter fat, it may be diluted with milk that contains only 3 per cent, of butter fat, because the result of such mixing, which will be milk averaging 4 per cent, of this food substance, will be the legal standard.

24. To prevent milk from souring, dishonest milk dealers often put into it such preservatives as soda, borax, and formaldehyde. There is no definite way of telling whether or not one of these has been used, except by a chemical analysis. However, if milk does not sour within a reasonable time when no precautions have been taken to keep it sweet, it should be looked on with suspicion, for it undoubtedly contains a preservative.

25. FRESHNESS OF MILK.--To be most satisfactory for all purposes, milk should be absolutely fresh. However, it is almost impossible to obtain milk in this condition, because it is generally sold at a distance from the source of supply. Milk that is sold in small towns and cities is usually 12 and often 18 to 21 hours old when it is delivered; whereas, in large cities, where the demand is so great that milk must be shipped from great distances, it is often 24 to 36 or even 48 hours old when it reaches the consumer. In order that milk may remain sweet long enough to permit it to be delivered at places so far removed from the source of supply, it must be handled and cared for in the cleanest possible way by the dealers. Likewise, if the housewife desires to get the best results from it, she must follow the same plan, cooling it immediately on delivery and keeping it cool until it is consumed. The freshness of milk can be determined only by the length of time it will remain sweet when proper care is given to it.

26. CLEANLINESS OF MILK.--Milk may be of the right composition, free from all adulteration, and as fresh as it is possible to obtain it, but unless it is clean, it is an injurious food. Milk is rendered unclean or impure by dirt. In reality, there are two kinds of dirt that may be present in milk, and it is important to know just what these are and what effect they have on milk.

27. The less harmful of the two kinds of dirt is the visible dirt that gets into the milk from the cow, the stable, the milker, the milking utensils, and similar sources when these are not scrupulously clean. If milk containing such dirt is allowed to stand long enough in pans or bottles for the heavier particles to settle, it will be found as sediment in the bottom of the receptacle. To say the least, the presence of such dirt is always disagreeable and frequently produces foreign flavors.

Straining the milk through clean absorbent cotton will reveal the presence of such dirt and another kind of dirt that does not show through the opaque fluid. This second kind of dirt is generally found in milk when the first kind is present in any quantity. It is more liable to be harmful than the other, because it enters the milk from the water used in cleaning the receptacles or from some contaminated source.

28. Whenever dirt is present in milk, bacteria are sure to be there; and the greater the quantity of dirt the greater will be the number of bacteria. Should the housewife desire to compare the cleanliness of several lots of milk, she may filter a like quantity from each lot, say a quart or a pint, through small disks of absorbent cotton. If, after the milk has passed through the cotton disk, very little dirt remains on it, as in Fig. 2 (_a_), the milk may be considered as comparatively clean; if the cotton disk appears as in (_b_), the milk may be said to be only slightly dirty; if it appears as in (_c_), the milk is dirty; and if it appears as in (_d_), the milk is very dirty. Milk that leaves a stain like that in (_d_) contains more bacteria than milk that leaves a stain like that in (_c_), and so on through all the lots of milk. Filtering milk in this manner, however, does not indicate whether the bacteria are disease producing. Such information can be secured only by microscopic examination, and only then by persons who have a knowledge of such matters.

29. Since, as has been pointed out, bacteria cling to all dirt, the dirt that milk contains is one of the causes of souring and putrefaction of milk, and may be a cause of disease. Indeed, it is definitely known that dirty milk sours much more quickly than does clean milk. Actual tests in which clean milk was put in a cool place have proved that it will keep for weeks, whereas dirty milk will sour in a day or two, especially in warm weather. This information should point out clearly to the housewife that it is not merely heat that changes milk or causes it to sour. She should understand in addition, that bacteria grow and multiply very rapidly when conditions for their growth are provided. These conditions are moisture, warmth, and the right kind of food, and as all of these are found in milk, this product is really ideal for bacterial development. The only way in which to protect milk is to make sure that no bacteria enter it, or, if they do, to make it impossible for them to grow. This may be done by keeping the milk so cold that they cannot thrive, or by destroying them in various ways, which are taken up later.

30. In former times, there was not much danger of wide-spread disease from the milk supply, for it was cared for almost entirely by those who kept a few cows and distributed milk to a small number of customers. In fact, it has been only within the past 50 years that large quantities of milk are handled by separate dairies and shipped great distances from the source of supply and that the distribution of milk has become a great industry. When so much milk is handled in one place, it is more or less unsafe unless the dairy is kept extremely clean and is conducted in the most sanitary manner. Experience has shown that too much attention cannot be given to the care of milk, for the lives of great numbers of children have been sacrificed through the carelessness of dairymen and persons selling and distributing milk, as well as through the negligence of those who handle the milk after it has entered the home. To overcome much of this carelessness, both the Federal Government and the various states of this country have set standards for safe milk production, and in order to make their laws effective have established inspection service. Independently of these state and national laws, many of the cities, particularly the large ones, have made their own standards, which, as a rule, are very rigid. One of the usual requirements is to compel each person who wishes to sell milk in the city to buy a license, so that the city authorities may keep in touch with those handling milk and so that conditions may be investigated at any time. In view of the care required of dealers in handling milk, the housewife owes it to herself and the members of her family to keep the milk in the home in the best possible manner.

GRADES OF CLEAN MILK

31. Ever since milk has come to be a commercial product, authorities have been devising ways in which it may be brought to the consumer in a condition that will permit it to be used without causing ill results. Their efforts have been rewarded to such an extent that nowadays consumers have little to fear from the milk they purchase, provided they get it from dealers who live up to the laws. Chief among the different grades of clean milk is _certified milk,_ and next in order comes _pasteurized milk,_ followed by _sterilized milk_.

32. CERTIFIED MILK.--The grade of clean milk sold under the name of certified milk is simply natural, raw milk that is produced and marketed under conditions that permit it to be guaranteed as pure, wholesome, and of definite composition. Such milk is necessarily higher in price than milk that is less wholesome and sanitary, because of the extra cost to the dairyman in meeting the requirements that make it possible for him to produce clean milk under sanitary conditions. These requirements pertain to the health and cleanliness of those who handle the milk, to the health, housing condition, and care of the herd and the dairy cows, and to the handling and care of milk in the dairy and during transportation and delivery. They are usually established and enforced by an inspection commission appointed by the city, county, or state in which the milk is produced.

33. If a little careful thought is given to the milk situation, it will be admitted that such precautions are necessary if clean milk is to be the result. Such milk cannot be produced if the surroundings are dirty, because dust and flies, which are two sources of contamination, are practically always present in such places. A stable with poor ventilation, without screens to keep out flies, and with floors that will not permit of cleaning, but cause filth and refuse to accumulate, is sure to contaminate milk that is handled in it. In addition, cows that are not well fed, comfortably housed, or carefully groomed cannot be expected to give milk of as good quality as cows that are properly cared for. Likewise, if the persons who do the milking are not clean, the milk is subject to contamination from this source.

34. All such unfavorable conditions can be remedied, and must be in the production of certified milk; but the good accomplished in this direction will be lost if the milk is carelessly handled after milking. Therefore, in producing certified milk, only the cleanest water available is allowed to be used in the dairy. Impure water is a common source of the contamination of milk in such places. On some farms, the water supply comes from a well that is too near the barn or that is too shallow to avoid being made impure by the germs that filter into it from the barnyard or a cesspool. If vessels in which milk is placed are washed in such water, it is necessary to sterilize them by boiling or steaming before milk is put into them, in order to kill the germs that come from the water. If such a precaution as this is not observed, the germs will multiply rapidly in the milk and, provided they are disease-producing, will make the milk extremely dangerous.

Besides observing the precautions mentioned, it is necessary that all utensils used in a dairy, such as pails for milking, strainers, containers, etc., be kept scrupulously clean. Likewise, they must be sterilized by boiling each time they are used, for, while disease germs may be absent, those which cause the milk to sour are always present and must be destroyed. Finally, to prevent any germs that enter milk from multiplying, even when it is properly cared for, the milk has to be cooled to a temperature of 45 degrees Fahrenheit or lower immediately after milking and then bottled in sterilized bottles, sealed, and packed in ice, within 20 minutes after milking.

35. It is by giving attention to all such matters that certified milk is possible. Such milk, as will be understood from what has been said, is neither a cooked milk nor a dirty milk that is processed, but a natural, raw milk that is clean at all stages of its production and marketing. Because of this fact, it is the best and cleanest milk to be had and may be used without hesitation, not only by grown persons in good health, but for infants and invalids.

The sanitary condition of certified milk and the consequent length of time it will remain sweet was demonstrated conclusively as far back as 1900 at the Paris Exposition. At this time, two model dairies in the United States--one located at the University of Illinois and the other at Briarcliff Manor, Westchester County, New York--delivered to their booths at the Exposition milk that was bottled under the most sanitary conditions at their dairies. During its transit across the ocean the milk was kept at a temperature of 40 to 42 degrees Fahrenheit, and on its arrival, 2 weeks after leaving the dairies, it was found to be in a perfectly sweet condition. Similar experiments made at later dates, such as shipping certified milk from the East to California, serve to bear out the test made in 1900, and prove what can be done with milk so produced as to be as free as possible from bacteria or the conditions that permit their growth.

36. PASTEURIZED MILK.--While certified milk is undoubtedly the safest kind of milk to use and is constantly growing in favor, much of the milk received in the home is pasteurized. By pasteurized milk is meant milk that has been heated to a temperature of 140 to 155 degrees Fahrenheit, kept at this temperature for 15 to 20 minutes, and then cooled rapidly. The result of such a treatment is that any disease-producing germs that are present in the milk, as well as those which are likely to cause intestinal disturbances, are destroyed, and that the milk is rendered safe as food for a time. Pasteurizing does not materially change the taste of milk, nor does it seriously affect the digestive properties of this food. It is true, of course, that pasteurized milk is not so good as clean raw milk. Still it is better to use such milk than to run the risk of using milk that might be contaminated with the germs of tuberculosis, typhoid fever, scarlet fever, diphtheria, or any other of the numerous diseases that have been known to be carried to whole families and communities through the milk supply.

37. Although pasteurizing is done on a large scale in dairies, there is no reason why the housewife cannot pasteurize the milk she buys, provided it is raw milk and she feels that it is not safe to use. If pasteurizing is to be done frequently and large quantities of milk are to be treated, it would be advisable to purchase the convenient apparatus that is to be had. However, if only a small quantity of milk is to be pasteurized at a time, a simple improvised outfit will prove satisfactory, because milk pasteurized in the home may be heated in the bottles in which it is received. Such an outfit consists of a dairy thermometer, a deep vessel, and a perforated pie tin or a wire rack of suitable size.

38. To pasteurize milk in the home, proceed in the manner illustrated in Fig. 3. Place the rack or invert the perforated pie tin in the bottom of the vessel, and on it place the bottles of milk from which the caps have not been removed. Make a hole through the cap of one bottle, and insert the thermometer into the milk through this hole. Then fill the vessel with cold water to within an inch or so of the top of the bottles, taking care not to put in so much water as to make the bottles float. Place the vessel over the fire, heat it until the thermometer in the bottle registers a few degrees over 150 degrees Fahrenheit, and keep the milk at this temperature for 15 to 20 minutes. At the end of this time, the milk will be sufficiently pasteurized and may be removed from the fire. As soon as it is taken from the water, cool it as rapidly as possible by running cold water into the vessel slowly or by placing the bottles in several changes of water, taking care not to place the hot bottles in very cold water at first, as this may cause them to crack.

When the milk has been cooled by some rapid method, keep it cool until it is used. This precaution is necessary because of the nature of pasteurized milk. The temperature at which milk is pasteurized is sufficient to kill all fully developed bacteria, but those which exist in an undeveloped state, or in the form of spores, develop very rapidly after pasteurization unless the milk is kept cold and clean. If these bacteria were allowed to develop, the purpose of pasteurization would be lost, and the milk would become as dangerous as it was originally. The advantage of cooling milk rapidly will be fully appreciated upon referring to Fig. 4, which illustrates the development of a single germ in milk that is cooled rapidly and in milk that is cooled slowly.

39. STERILIZED MILK.--By sterilized milk is meant milk in which all germs are destroyed by sterilization. Such milk is not sold by dealers, but the process of sterilization is resorted to in the home when pasteurization is not sufficient to render milk safe. This process, which is the only positive means of destroying all germs, consists in bringing the milk to the boiling point, or 212 degrees Fahrenheit, allowing it to boil for three quarters of an hour, and then cooling it rapidly. One who undertakes to treat milk in this way should remember that it is difficult to boil milk, because the solids in the milk adhere to the bottom and sides of the vessel and soon burn. However, this difficulty can be overcome by sterilizing the milk in the bottles in which it is bought.

40. To sterilize milk, place the sealed bottles on a wire rack or a perforated pie tin in a deep vessel, as for the pasteurizing of milk, and pour cold water into the vessel until it nearly covers the bottles. Then raise the temperature of the water quickly to the boiling point, and after it has begun to bubble, allow it to boil for three quarters of an hour. At the end of this time, cool the milk rapidly and then keep it cool until it is used.

41. Although milk thus treated becomes safe, sterilization changes its flavor and digestibility. If milk of this kind must be used, some raw food should be given with it. A diet composed entirely of cooked food is not so ideal as one in which some raw food is included, because raw foods contain substances that are essential to health. The change that takes place in the composition of milk that has been sterilized can be easily observed. Such milk on becoming sour does not coagulate as does pasteurized or raw milk, owing to the fact that the lime salts in the milk are so changed by the high temperature as to prevent the thickening process from taking place. Then, too, sterilized milk is not likely to become sour even after considerable time. Still, such milk is not safe to use except when it is fresh, for instead of fermenting in the usual way it putrefies and is liable to cause such a dangerous sickness as ptomaine poisoning.

42. MODIFIED MILK.--For infants who cannot be fed their normal diet, cow's milk must be used as a substitute, but in order to make it a more nearly ideal food for them it must usually be modified, or changed, by adding other materials. When it is so treated, it is known as modified milk. The materials used to modify milk are sterile water, lime water, barley water, cream, skim milk, milk sugar, or some other easily digested carbohydrate, one of these or a combination of them always being employed. The proportion of these ingredients to use varies with the age of the child that is to be fed and must be constantly changed to meet the child's requirements. In the production of modified milk, a physician's prescription and directions should always be followed closely. Only the best quality of milk should be used, and, in addition, the greatest care should be taken to have all the bottles, utensils, and materials used as clean and sterile as it is possible to make them. If such conditions cannot be met, it is advisable to pasteurize the modified-milk mixture after the materials have been put together.

PRESERVED MILK

43. Besides milk that is commonly sold by dairymen and milk dealers, it is possible to buy in the market many grades of so-called PRESERVED MILK. Such milk is produced by driving off all or part of the water contained in milk, and it is sold as _condensed, evaporated,_ and _powdered milk_. Usually, it is put up in tin cans, and while it is not used so extensively as regular milk, many firms are engaged in its preparation.

44. CONDENSED AND EVAPORATED MILK.--As has just been mentioned, condensed and evaporated milk is produced by the complete or partial evaporation of the water contained in milk. Such milk can be shipped long distances or kept for long periods of time, because it does not contain sufficient moisture to permit the growth of bacteria. In evaporating milk to produce these preserved milks, each gallon is diminished in quantity to about two and one quarter pints, the original 87 per cent. of water being reduced to about 25 per cent. Therefore, in order to use such milk, sufficient water must be added to restore it to its original composition. Sometimes comparatively large amounts of cane sugar are added to such milks, which, besides sweetening them, assist in their preservation. If cane sugar is not used, the milks are usually made sterile in order to prevent them from spoiling.

45. POWDERED MILK.--The form of preserved milk known as powdered milk is the result of completely evaporating the water in milk. Such milk has the appearance of a dry powdered substance. It does not spoil easily and is so greatly reduced in quantity that it can be conveniently stored. Because of these characteristics, this product, for which skim milk is generally used, is extensively manufactured. It is used chiefly by bakers and confectioners, and, as in the case of evaporated or condensed milk, the water that has been evaporated in the powdering process must be supplied when the milk is used.

STANDARD GRADING OF MILK AND CREAM

46. In order that a definite idea may be formed of the sanitary and bacteriological standards that are set by milk commissions, there are here given, in Table I, the regulations governing the grades and designation of milk and cream that may be sold in the city of New York. As will be observed from a study of this table, only definite grades of milk and cream can be sold in that city; likewise, it must conform to certain standards of purity and the producer must handle it in such a way that it may be delivered to the consumer in as clean and fresh a condition as possible.

Without doubt, a grading similar to this one will become general throughout the United States eventually, for this is the only way by which the housewife may know with certainty whether or not the milk she purchases is of the right composition and is safe, fresh, and sanitary in every respect. The different qualities of milk and cream as shown by this grading are, of course, sold at different prices, those which require the greatest care and expense in handling selling for the highest price.

MILK IN THE HOME

PURCHASE OF MILK