( Originally Published Early 1900's )
Milk weighs a little more than water. One quart weighs two pounds two and one-half ounces.
Milk is one of the most important protein foods. It should be very clean as it is used by many people with poor digestion and if it is not pure it may do great harm. Before opening a bottle of milk, wash the bottle and top carefully and wipe dry. What is the composition of milk
Color. Good milk is yellowish white and free from specks or streaks. The milk of some breeds of dairy cows looks whiter than that of others. Cows fed on dry feed do not give very yellow milk. Bluish milk is poor. There should be no sediment at the bottom after milk stands. Strain milk through cheese-cloth and see if specks of blood, or pus, or yellowish specks are .found ; if so, the milk is from cows with diseased udders ; distinguish carefully between curdy specks and fat globules. Pure rich milk clings to the glass.
The Odor of Milk. Fresh clean milk is pleasantly sweet, with no trace of mustiness. Unpleasant odors may be caused by dirt in the milk or by the food of the cow.
The Taste. Fresh milk is slightly sweet with no strong taste. The flavor is spoiled by the same conditions that cause unpleasant odors.
Why Milk Sours. Milk sours because bacteria find their way into it from the dust, or from unclean vessels, and change the sugar to an acid. When sufficient acid is formed, the casein (sometimes called ''curd'') is curdled or made solid. The cleaner the milk, the fewer. the bacteria. Milk produced under the best conditions may' have as low a bacterial count as eight thousand per cubic centimeter (about 15 drops). Ordinary market milk has fifty thousand per cubic centimeter. Other bacteria than those that cause souring are found in dirty milk in great numbers. Such milk may decompose or spoil before it sours.
A poison known as ptomaine is sometimes found in milk, cream, buttermilk, and ice cream made from old or unclean milk and cream; it is very dangerous, and often causes violent illness or even death.
Keeping Milk. The two things to remember in keeping milk are: first, it must be kept clean so that few bacteria may enter it; second, it must be cooled quickly and kept cool, to prevent those bacteria that enter from multiplying rapidly. Milk may be cooled in ice water as soon as it is drawn from the cow, then kept in a very cool place. If you have no ice-box, wrap the milk vessel in a wet cloth. Tin and poorly glazed earthenware and vessels with seams or cracks should not be used for keeping milk ; glass or semi-porcelain is best. Do not let milk freeze, and never mix warm milk with that which has been cooled.
MILK AS A CARRIER OF DISEASE
Milk contains the food upon which bacteria thrive, and as it is commonly taken raw we must guard our supply carefully. Cows sometimes have tuberculosis and the germs may be carried in their milk. Not only the cows, but all workers in dairies, should be tested for tuberculosis. The germs of typhoid fever, diphtheria, scarlet fever, and some bowel diseases of young children may be carried in milk, if it is handled by persons who have the disease or who have been in contact with it. Never carry a milk bottle into a sick room. If there are any contagious diseases in the house, have milk bottles sterilized, that is, heated, so that all the germs are destroyed, before returning them to the dairyman. If there is danger of disease, or if one wishes to keep milk sweet for several days, it may be sterilized. Pasteurization, or the heating of milk to a temperature of 145-160° F., is adopted for the purpose of keeping it sweet. This process destroys the germs of some diseases, but can not be absolutely depended on to kill all germs. Milk should not be kept more than thirty-six hours after Pasteurization.
Heat the milk to 212° F. and keep boiling for one hour. For long keeping, boil for three successive days, and seal. Milk so heated, however, is difficult to digest.
1. Fill both parts of the double boiler with water. The .depth of the inner compartment should be such that when the bottles are placed therein the height of the water will be slightly above the height of the milk in the bottles.
2. Place the double boiler on the stove and put the bottles containing the milk to be Pasteurized in the water of the inner compartment. The tops of, the bottles should be tightly stoppered with sterile non-absorbent cotton.
3. Place a dairy thermometer in the water. When the temperature reaches 150° F. (or when fine bubbles appear in the milk), remove the double boiler to the rear of the stove and allow it to stand covered for thirty or forty minutes.
4. The milk must be chilled quickly. Set the bottles in a large dish pan or bread pan containing cold water. A single bottle can best be quickly chilled by holding the side of the bottle under running water at such an angle that the milk is not spilled or the cotton plug allowed to become wet.
5. As soon as the milk is cold it should be set in the ice compartment of the ice-box until needed. All Pasteurized milk more than twenty-four hours old should be thrown away.
Milk is a protein or building food, although it contains fat and carbohydrate in the form of sugar. The protein of milk is in the form of casein, with a little albumin. The next most important substance is fat. The fat varies with the breed of the cows, being from 3% to 6%. What breeds of cows give very rich milk?
There is about 5% carbohydrate in milk in the form of lactose (or milk sugar). The minerals in milk are very important; they .furnish bone and muscle. They are phosphate of lime, phosphate of potash, and a trace of iron and citric acid, which may be considered with the minerals. Water forms about 87% of milk. Cow's milk is not a' perfect food, although it is very valuable in the diet.
By a series of experiments milk may be separated into its various parts.
EXPERIMENT I. Observe a bottle of milk kept in a cool place over night; note the depth of the cream. In good milk from one-eighth to one-third is cream.
EXPERIMENT II. Keep a half pint of thick cream in a .cool place for twenty-four hours. Cool to 55° F. and beat with a fork in a bowl. Churn in a small glass churn, or shake in a preserve jar until the butter separates. The grains should be about the size of grains of corn. Press gently to re-move the buttermilk. Drain and wash the butter in clean cold water. Sprinkle on one-half teaspoonful of salt and work it in. Handle butter very lightly so as not to spoil the grain or texture. Weigh the butter. How much did it cost? What is the composition of the buttermilk?
If preferred, a quart of rich milk may be put into a bowl in a cool place until the cream rises and is quite thick. It may be skimmed and churned as directed above. Perfectly sweet separator cream may be churned, but the butter lacks flavor. Most persons prefer butter from well ripened sour cream.
EXPERIMENT III. Scald a half cup of milk. Note the skin that forms on the top of the milk; this is chiefly albumin. The protein of milk is hardened by a high temperature; for this' reason it is heated over hot water. Milk scorches easily because of the fine particles of casein in it, and heating it over hot water prevents this.
EXPERIMENT IV. Put a quart of milk into a bowl and keep it in a moderately cool place until it clabbers or coagulates; turn into a thin cloth bag and hang up to drain. After several hours place in a. pan and put a weight on it; when firm remove from the bag and serve with cream and sugar. Note the consistency. What food elements have been lost in its preparation ?
EXPERIMENT V. The water that drains from clabber is known as whey. It contains a little of the protein and some of the sugar of milk. Boil a portion of the whey. Let stand for a few moments. What can you say of the composition of the skin which forms,
EXPERIMENT VI. To a cup of fresh lukewarm milk add one-fourth of a rennet tablet, dissolved in one tablespoonful of lukewarm water. Let stand until it becomes firm; then compare with the curd in Experiment IV.
EXPERIMENT VII. Warm one cup of sweet skimmed milk to about 110° F. Add vinegar, a drop at a time, stirring constantly until it curdles. Let stand until the curd settles. Then drain off the liquid, filter, and boil. Skim it, let settle, strain through muslin; then filter the boiled liquid, and evaporate to dryness in a tiny pan. What is the product? Exhibit commercial milk sugar to classes.
THE DIGESTION OF MILK
The first step in the digestion of milk takes place in the stomach. It is then clotted or changed to curd by the action of rennet, a digestive ferment. (See page 49.) Sip milk slowly; the liquid of the mouth dilutes the milk and makes the curd less dense. Buttermilk and clabber are easier to digest than fresh milk, as the curd is finely divided. Very rich milk is not as digestible as that only moderately rich. Why? Owing to the ease with which milk is digested, it is very valuable in sickness, although in some persons it causes constipation. As milk does not form the poisons that other animal proteins do in the process of digestion, it is very useful when there is a tendency to rheumatism, gout, kidney diseases, and colds.
Milk should not be used with acid foods, such as fruits and fruit juices, as a dense clot forms that is not easy to digest. Only rich cream should be served with peaches or berries. Why ?
THE COST AND FOOD VALUE COMPARED
If we consider the actual nutrients contained, milk even at ten cents a quart is not an expensive food. A quart of milk equals in food value three-fourths of a pound of meat, eight eggs, or six ounces of bread. A five cent loaf of bread weighs from twelve and one-half to seventeen ounces. Bread, therefore, is a cheaper food than milk, but lacks protein. A glass of milk equals three ounces of lean beef or two eggs. With beef at eighteen cents a pound and eggs at thirty cents a dozen, milk at ten cents a quart is the cheapest food. A family of five can afford to use three quarts of milk each day.
If good milk is purchased at night the cream may be used for breakfast, leaving an abundance of skim milk of good quality for household use. If a quart of milk, which contains 4% of fat, is kept cool for eight hours or over night, the upper six ounces will form a 16% cream ; the upper eleven ounces a 10% cream. The cream may be removed with a milk dipper or by syphon as shown in the figure, or it may be poured off. A pint of cream weighs sixteen ounces and costs the same as two quarts of milk, which would furnish twelve ounces of 16% cream or twenty-two ounces of 11% cream, and would leave skim milk for cooking purposes.
What is the fat content of your cream? What is the fat content of the milk you buy? What is the price of milk and cream in your market? Which will give you the more food value,—two quarts of milk at ten cents a quart or a pint of cream at twenty cents? Which would be of more value in your housekeeping?
Remember that milk is a food, not a drink. It takes the place of meat, beans, and eggs. It combines well with eggs, and if a moderate quantity of each is used, they will together equal a ration of meat or beans. It is particularly desirable for children up to twelve years of age, as it is quite readily assimilated. For supper or breakfast, mush and milk costs no more than bread and jam or molasses and forms a ration more in accord with the child's needs.
Skim Milk. For such foods as breads and cream soups, skim milk may be used to increase the amount of protein in the diet. Sour milk may be used for making bread and cottage cheese.
Condensed and Evaporated Milk. This is canned milk from which a portion of the water has been removed. (Note difference in amount of water as compared with fresh milk.) Condensed milk ordinarily means milk to which cane sugar has been added. Such milk may be substituted for fresh milk in many cases, but the flavor is not that of the fresh article.
Evaporated Cream. This is usually condensed milk with no added sugar, and resembles cream only in appearance.
QUESTIONS AND PROBLEMS
Give tests for good milk. What are your state or city laws regarding cleanliness in dairies? Is there any inspection or test for tubercular or other diseased animals? Visit the dairy from which your milk supply comes. Is your milk supply clean enough to be used without Pasteurization? What diseases may be carried in milk? Is Pasteurization a safe remedy for all disease germs? Why does milk sour? How can souring be delayed? What conditions are favorable to the growth and spread of bacteria? (See Yeast, page 210.) Should cows be fed hay while being milked? How could the dust be lessened in dairy barns and pens? What is the bacteriological count for market milk in your town? What is meant by this term? If certified milk is sold, what is the difference between the bacteria permissible in it and in ordinary milk? Tell how we can keep milk. How can you air milk quickly so that it will not be exposed to dust? Give directions for washing milk vessels. What is the cost of milk in your home? Give the standards for milk and cream in your state. What foods do we find in milk? Why is milk scalded over hot water? Why not serve a pudding of milk and eggs after a meal with much meat? How may skim milk be utilized? What is its food value?