Science in the Kitchen / A Scientific Treatise On Food Substances and Their Dietetic Properties, Together with a Practical Explanation of the Principles of Healthful Cookery, and a Large Number of Original, Palatable, and Wholesome Recipes

by E. E. Kellogg

MILK.

hemically considered, the constituents of milk are nitrogenous matter (consisting of casein and a small proportion of albumen), fat, sugar of milk, mineral matter, and water, the last constituting from sixty-five to ninety per cent of the whole.

The proportion of these elements varies greatly in the milk of different animals of the same species and of the same animals at different times, so that it is not possible to give an exact analysis.

The analysis of an average specimen of cow's milk, according to Letheby, is:—

Nitrogenous matter	4.1
Fat	3.9
Sugar of milk	5.2
Mineral matter	0.8
Water	86.0

If a drop of milk be examined with a microscope, it will be seen as a clear liquid, holding in suspension a large number of minute globules, which give the milk its opacity or white color. These microscopic globules are composed of fatty matter, each surrounded by an envelope of casein, the principal nitrogenous element found in milk. They are lighter than the surrounding liquid, and when the milk remains at rest, they gradually rise to the top and form cream. Casein, unlike albumen, is not coagulated by heat; hence when milk is cooked, it undergoes no noticeable change, save the coagulation of the very small amount of albumen it contains, which, as it solidifies, rises to the top, carrying with it a small portion of the sugar and saline matter and some of the fat globules, forming a skin-like scum upon the surface. Casein, although not coagulable by heat, is coagulated by the introduction into the milk of acids or extract of rennet. The curd of cheese is coagulated casein. When milk is allowed to stand for some time exposed to warmth and air, a spontaneous coagulation occurs, caused by fermentative changes in the sugar of milk, by which it is converted into lactic acid through the action of germs.

Milk is sometimes adulterated by water, the removal of more or less of the cream, or the addition of some foreign substance to increase its density.

The quality of milk is more or less influenced by the food upon which the animal is fed. Watery milk may be produced by feeding a cow upon sloppy food.

The milk of diseased animals should never be used for food. There is no way by which such milk can invariably be detected, but Prof. Vaughan, of Michigan University, notes the following kinds of milk to be avoided:

1. Milk which becomes sour and curdles within a few hours after it has been drawn, and before any cream forms on its surface. This is known in some sections as 'curdly' milk, and it comes from cows with certain inflammatory affections of the udder, or digestive diseases, or those which have been overdriven or worried.

2. "Bitter-sweet milk" has cream of a bitter taste, is covered with 'blisters,' and frequently with a fine mold. Butter and cheese made from such milk cannot be eaten on account of the disagreeable taste.

3. 'Slimy milk' can be drawn out into fine, ropy fibers. It has an unpleasant taste, which is most marked in the cream. The causes which lead to the secretion of this milk are not known.

4. 'Blue milk' is characterized by the appearance on its surface, eighteen or twenty-four hours after it is drawn, of small, indigo-blue spots, which rapidly enlarge until the whole surface is covered with a blue film. If the milk be allowed to stand a few days, the blue is converted into a greenish or reddish color. This coloration of the milk is due to the growth of microscopic organisms. The butter made from 'blue milk' is dirty-white, gelatinous, and bitter.

5. 'Barnyard milk' is a term used to designate milk taken from unclean animals, or those which have been kept in filthy, unventilated stables. The milk absorbs and carries the odors, which are often plainly perceptible. Such milk may not be poisonous, but it is repulsive.

There is no doubt that milk often serves as the vehicle for the distribution of the germs of various contagious diseases, like scarlet fever, diphtheria, and typhoid fever, from becoming contaminated in some way, either from the hands of milkers or from water used as an adulterant or in cleansing the milk vessels. Recent investigations have also shown that cows are to some extent subject to scarlet fever, the same as human beings, and that milk from infected cows will produce the same disease in the consumer.

Milk should not be kept in brass or copper vessels or in earthen-ware lined with lead glazing; for if the milk becomes acid, it is likely to unite with the metal and form a poisonous compound. Glass and granite ware are better materials in which to keep milk.

Milk should never be allowed to stand uncovered in an occupied room, especially a sitting-room or bedroom, as its dust is likely to contain disease-germs, which falling into the milk, may become a source of serious illness to the consumer. Indeed it is safest to keep milk covered whenever set away, to exclude the germs which are at all times present in the air. A good way is to protect the dishes containing milk with several layers of cheese-cloth, which will permit the air but not the germs to circulate in and out of the pans. Neither should it be allowed to stand where there are strong odors, as it readily takes up by absorption any odors to which it is exposed.

A few years ago Dr. Dougall, of Glasgow, made some very interesting experiments on the absorbent properties of milk. He inclosed in jars a portion of substances giving off emanations, with a uniform quantity of milk, in separate vessels, for a period of eight hours, at the end of which time samples of the milk were drawn off and tested. The result was that milk exposed to the following substances retained odors as described:—

Coal gas, distinct; paraffine oil, strong; turpentine, very strong; onions, very strong; tobacco smoke, very strong; ammonia, moderate; musk, faint; asafetida, distinct; creosote, strong; cheese (stale), distinct; chloroform, moderate; putrid fish, very bad; camphor, moderate; decayed cabbage, distinct.

These facts clearly indicate that if the emanations to which milk is exposed are of a diseased and dangerous quality, it is all but impossible that the milk can remain free from dangerous properties.

Too much pains cannot be taken in the care of milk and vessels containing it. Contact with the smallest quantity of milk which has undergone fermentation will sour the whole; hence the necessity for scrupulous cleanliness of all vessels which have contained milk before they are used again for that purpose.

In washing milk dishes, many persons put them first into scalding water, by which means the albumen in the milk is coagulated; and if there are any crevices or seams in the pans or pails, this coagulated portion is likely to adhere to them like glue, and becoming sour, will form the nucleus for spoiling the next milk put into them. A better way is first to rinse each separately in cold water, not pouring the water from one pan to another, until there is not the slightest milky appearance in the water, then wash in warm suds, or water containing sal-soda, and afterward scald thoroughly; wipe perfectly dry, and place if possible where the sun will have free access to them until they are needed for further use. If sunshine is out of the question, invert the pans or cans over the stove, or place for a few moments in a hot oven.

The treatment of milk varies with its intended use, whether whole or separated from the cream.

Cream rises best when the milk is quite warm or when near the freezing-point. In fact, cream separates more easily from milk at the freezing-point than any other, but it is not thick and never becomes so. An intermediate state seems to be unfavorable to a full rising of the cream.

A temperature of 56° to 60°F. is a good one. Milk to be used whole should be kept at about 45° and stirred frequently.

All milk obtained from city milkmen or any source not certainly known to be free from disease-germs, should be sterilized before using. Indeed, it is safest always to sterilize milk before using, since during the milking or in subsequent handling and transportation it is liable to become infected with germs.

To Sterilize Milk for Immediate Use.—Put the milk as soon as received into the inner dish of a double boiler, the outer vessel of which should be filled with boiling water. Cover and heat the milk rapidly to as near the boiling point as possible. Allow it to remain with the water in the outer boiler actively boiling for half an hour, then remove from the stove and cool very quickly. This may be accomplished by pouring into shallow dishes, and placing these in cold water, changing the water as frequently as it becomes warm, or by using pieces of ice in the water. It is especially important to remember that the temperature of the milk should be raised as rapidly as possible, and when the milk is sufficiently cooked, cooled very quickly. Either very slow heating or slow cooling may prove disastrous, even when every other precaution is taken.

Or, well-cleaned glass fruit cans may be nearly filled with milk, the covers screwed on loosely, then placed in a kettle of cold water, gradually heated to boiling and kept at that temperature for a half hour or longer, then gradually cooled. Or, perfectly clean bottles may be filled with milk to within two inches of the top, the neck tightly closed with a wad of cotton, and the bottles placed in a steam cooker, the water in which should be cold at the start, and steamed for half an hour.

This cooking of milk, while it destroys many of the germs contained in milk, particularly the active disease-germs which are liable to be found in it, thus rendering it more wholesome, and improving its keeping qualities somewhat, does not so completely sterilize the milk that it will not undergo fermentative changes. Under varying conditions some thirty or forty different species of germs are to be found in milk, some of which require to be subjected to a temperature above that of boiling water, in order to destroy them. The keeping quality of the milk may be increased by reboiling it on three successive days for a half hour or longer, and carefully sealing after each boiling.

To Sterilize Milk to Keep.—This is a somewhat more difficult operation, but it may be done by boiling milk sealed in very strong bottles in a saturated solution of salt. The milk used should be perfectly fresh. It is best, when possible, to draw the milk from the cow directly into the bottles. Fill the bottles to within two inches of the top, cork them immediately and wire the corks down firmly and place them in the cold salt solution. Boil fifteen minutes or half an hour. Allow the solution to cool before removing them. If the bottles are removed from the solution while hot, they will almost instantly break. When cold, remove the bottles, and cover the tops with sealing wax. Store in a cool place, shake thoroughly once or twice a week. Milk sterilized in this manner will keep indefinitely.

Condensed Milk.—Condensed milk is made by evaporating milk in a vacuum to one fifth its original volume; it is then canned like any other food by sealing at boiling temperature in air-tight cans. When used, it should be diluted with five times its bulk of warm water.

Condensed milk, when not thoroughly boiled in the process of condensation, is liable to harbor disease-germs the same as any other milk.