CHAPTER XVII
MILK
COMPOSITION OF MILK
Milk as a Food
Milk contains all the elements necessary in a balanced diet for the adult and furnishes an almost perfect food for the suckling. Milk is lacking in iron and roughage and is therefore not suitable for the sole diet of adults. This is compensated for in the infant by a large amount of iron which is contained in the spleen and furnishes this necessary element during the suckling period. There is no other single food that will so well promote the growth and development in young children. Milk is easily digested, is palatable, and forms one of our best and most important articles of food. It is asserted that the consumption of milk in the United States will average about 0.6 of a pint per capita per day. In many countries there is practically no milk used. In the United States about 16% of the dietary consists of milk and its products.
Milk is an animal secretion produced by the mammary gland and is exceedingly complex in its composition. It consists chiefly of water containing various solids in solution. Cow’s milk consists of 87% water and 13% solids. The solids consist of fats in emulsion, milk sugar, albumin, casein and mineral matter. Milk also contains such gases as oxygen, nitrogen and carbon dioxide. It contains enzymes, phosphatids and vitamins, also antibodies and other substances.
Fresh normal milk is an opaque fluid of white or yellowish-white color and has a sweetish taste and rather pleasant odor. In reaction milk is amphoteric, that is, it is acid to litmus and alkaline to turmeric. The specific gravity of cow’s milk is from 1.027 to 1.035. Under the microscope it is found to contain fat globules and cells, also bacteria and other objects. The oxygen and nitrogen that are found in milk are thought to be carried into it mechanically from the air during the process of milking. Lecithin, cholestrin, citric acid, lactosin, orotic acid and ammonia are found in milk in small quantities.
Proteins
Casein, lactalbumin, and lactoglobulin are the three proteins found in milk and are usually constant in a given species.
Casein is found nowhere in nature except in the secretion of the mammary glands. It is highly specialized and, as a nucleoalbumin, contains a certain amount of phosphorus. Lactalbumin is a protein found in quantities varying from 0.2% to 0.8%. It is similar to the serum albumin in blood and coagulates at 70° C. There is a mere trace of lactoglobulin in milk. It is insoluble in water.
Fat
Milk contains fat in emulsion; that is, the fat is suspended in the serum of milk in the form of emulsion. The fat is lighter than the milk serum and therefore rises to the top in the form of cream, or the fat may be separated from the milk by centrifugal force. Cream does not consist in fat globules alone but contains the same constituents as the milk, only it is very much richer in fat. By agitating the cream, as in a churn, or by means of shaking, the fat globules will coalesce and form into lumps of butter. It is stated by some authors that cream contains a larger number of bacteria than skim milk. The fore milk, or that which is first milked from the udder, has a small amount of fat; the last that is taken, which is known as the strippings, may contain as much as 9% or 10% of fat. An increase in the temperature of the milk will retard the rising of the fat and if the temperature is kept above 65° C. for any length of time, cream will not form on top. Therefore, it follows that a moderately low temperature will increase the rapidity with which fat rises to the top of the milk.
Parkes says, “Milk should not have less than 12.5% of total solids of which 3.5% is fat and 0.7% is salts; ... the percentage of cream by volume not less than 10%.”
Infants placed on a diet of milk that is too rich in fats will thrive for a while, but in time will lose weight and show other symptoms, indicating the inability of Innate to digest the food. The stools become hard and dry, of a pale color and composed largely of fat soaps. This shows that Innate is unable to furnish sufficient alkaline bases through the body to saponify the excessive amount of fat in the intestines. This results in a condition resembling acidosis.
Vitamins
Milk is found to contain all three vitamins, A, B, and C, known as the fat-soluble A, water-soluble B, and water-soluble C. Cream is rich in vitamin A. This vitamin increases growth and promotes nutrition and is therefore valuable in the diet of the young. Vitamin A and B are not destroyed by heat, unless it be a very great degree for a long period of time; they also resist drying and age. For this latter reason milk may be used in cooking and still retain the virtues of these two vitamins, as well as do evaporated milk and dried milk. Vitamin C is impaired and may be completely destroyed by high temperature and deteriorates with age and with drying. There is no article of food (diet) that is superior to milk in dietetic and nutritional value, and especially is this true of butter fat. The standard by which milk is tested is the amount of butter fat it contains.
Lactose or Milk Sugar
Milk contains what is known as milk sugar or lactose. It is white crystalline sugar, has a slightly sweet taste and is soluble in water. When acted upon by microörganisms it is changed into glucose, and the glucose is then reduced to lactic acid, the lactic acid being the cause of the milk souring. Milk sugar is found nowhere else in Nature.
SANITARY MEASURES IN PRODUCTION
Milk, a Germ Medium
Milk, because of its characteristic qualities, forms a medium in which all kinds of bacteria and germs, or low forms of life, thrive. When we consider the processes necessary to obtain the milk and deliver it to the consumer, even though the most rigid sanitary methods are observed, it can readily be seen that milk is exposed to almost all kinds of dirt and to the different forms of organisms.
It is very difficult to obtain milk in a state of purity and if germs played as important a part in the production of dis-ease as is thought by some, one of the most important articles of diet would be lost to mankind. Great quantities of these germs are ingested into the stomach of individuals who drink milk.
These bacteria are carried into the milk during milking and in the handling of the milk and the retainers. Bacteriological standards have been established, but vary a little with different authors. Usually it is agreed that certified milk should not contain more than 10,000 bacteria per cubic centimeter. Market milk should not have more than 1,000,000 bacteria per cubic centimeter in the raw state and not more than 50,000 per cubic centimeter after pasteurization.
It can be seen by this standard that even the relatively pure milk contains great numbers of bacteria and yet these bacteria are ingested into the digestive tract and no harm done. As a matter of fact, this helps to substantiate the contention of Chiropractic that these germs and the different bacteria are essential to life. There is no question, however, that poisons may be contained in milk, and when these are taken into the stomach Innate may not be able to properly adapt the tissues and thus a toxic condition will be produced.
Because of the characteristic qualities of milk, the strictest sanitary measures should be observed in all the processes involved, from the time the milk is taken from the cow until it is delivered to the customer.
Milk undergoes certain physical, chemical and biological changes as soon as it is taken from the cow: the cream rises and thus it is separated from the milk; there is also a separation of the solids from the fluids.
Care in the Milking
A sanitary environment should be provided for the cows and special care should be taken in the process of milking to prevent the milk from becoming contaminated with dirt and filth. Those who handle this milk should take proper precautions to prevent dirt from getting into it. All utensils should be kept clean, sweet and free from sour milk.
Sanitary measures should include: Proper care and feeding, or the health of the milch cows; (2) proper regulation of the bottling and transportation of the milk. The cows should by all means be healthy, inasmuch as milk is an animal secretion. It is certain that if the animal is suffering from dis-ease, this secretion will not be normal. Over-exertion and fright will also affect the milk. Care must be exercised to detect dis-ease and such dis-eased animals should be separated from the herd and their milk not used.
Care of the Cows
The cows should have plenty of exercise, but care should be taken that they are not frightened or over-exerted. They should be provided with proper protection from the weather and should have plenty of fresh hay, ground whole grain, and, when possible, be allowed to graze. Spoiled vegetables or fruits, foul or fermented foods are detrimental to dairy cows. A proper supply of salt is necessary and plenty of pure, fresh water is absolutely essential for the health of cows.
Barns and Barnyards
The barns and barnyards where milch cows are kept should be free from manure, pools of stagnant water, dirt and refuse. The ground should be well drained so that it will not become water-logged. Such ground should be located on elevations to assure proper drainage. The habit of allowing the refuse to accumulate in large quantities before hauling it away is not only repulsive but very unsanitary and may become a source of pollution of the milk supply.
Stable should be constructed to assure proper ventilation and to provide proper shelter for the animals. The floors should be of material that is non-absorbent, well drained, and easily cleaned. Concrete is best. Each cow should have a separate stall furnished with a stanchion. The walls should be of material that can be cleaned. There should be 600 cubic feet space for each cow in the barn.
Bottling
Milk should be strained through gauze placed over the wire strainer. All the utensils should be thoroughly cleaned after each milking and, if possible, sterilized in a steam sterilizer. The straining should not be done in the barns where the cows are, but in special separate milk houses. The bottling should be done only in establishments specially fitted for such purpose.
Proper Temperature
Milk should be kept at a temperature not above 50° F. during transportation. The cans or bottles should be properly covered, sealed, and the milk protected from too much agitation.
Because milk undergoes a very rapid change, beginning almost as soon as it is drawn from the cow, it is necessary to either consume it in a short time or provide some means of preserving it. Milk soon deteriorates, becomes sour and unfit for use as food.
The best means of preserving milk is to keep it at a low temperature. Bacteria are not destroyed in low temperature, but the activity is inhibited and their development retarded. In this way milk is kept from souring and from undergoing fermentative changes. The digestibility and character of milk are not changed by cold, and it will be sweet for a day or even longer if kept at a temperature under 50° F.
An entirely sterile milk may be furnished only by raising the temperature to 248° F. for at least two hours, but this destroys the milk ferments. There are certain changes produced by boiling milk which renders it less desirable for food, making it less digestible. It is, therefore, especially undesirable for infants.
PREPARATION OF MILK AND MILK PRODUCTS
Pasteurization of Milk
In pasteurizing milk it is heated to a temperature of 60° C. (140° F.) for a period of twenty minutes. This destroys the so-called pathogenic germs, yet does not destroy the ordinary milk ferments. It does not change its digestibility nor alter the taste or appearance.
All of the so-called pathogenic germs, such as tuberculosis, typhoid, dysentery and diphtheria, for example, are completely destroyed by pasteurization, but the ferments are not destroyed and the milk is in no way altered. This process may be accomplished on a large scale and thus furnish as safe milk for commercial consumption. Pasteurized milk should be rapidly cooled after heating, and if kept cool furnishes a clean, healthy milk entirely safe and satisfactory for infant food as well as for adults.
Pasteurization furnishes a purified milk but not a pure milk. It is undoubtedly the best means of preservation and may be considered as bearing the same relation to purification of milk as filtration bears to purification of water.
The use of formaldehyde, borax and boracic acid is as objectionable in artificial preservation of milk as in the preservation of meat and other foods and should not be tolerated.
Condensed Milk
Milk is condensed by removing some of the water. It is made either from skim or whole milk. It may be unsweetened or sweetened with cane sugar. Condensed and evaporated milk should contain a label stating the grade of milk used. Condensed and evaporated milk are poor in vitamin C.
Dry Milk
It has been found that by certain processes it is possible to dry milk, taking all the water out and leaving a powder. This may be accomplished and still retain most of the nutritive value of the milk. Vitamin fat soluble A and water soluble B remain practically the same, but water soluble C vitamin is diminished. Babies fed on dried milk will thrive, but orange juice or some other food containing antiscorbutic properties must be given to compensate for the loss of vitamin C. Dried milk provides an adequate supply to many parts of the country and to the cities, where it is difficult to obtain fresh milk.
Butter
Butter is produced by placing cream in a proper apparatus and agitating or churning it until the fat globules coalesce into lumps. These lumps are then taken out of the serum known as the buttermilk and the water and milk worked out until it becomes more or less solid. When butter has had the milk and water worked out of it the constituents should be in about the following proportions: Fat, 83.5%; curd, 1.0%; ash, 1.5%; milk sugar, 1.0%; water, 13.0%. By weight butter should never contain more than 16% of water and should contain at least 80% of fat.
Owing to the conversion of the fat into fatty acids butter will, in the course of time, become acid, rancid and unfit for table use.
Oleomargarine is a product resembling butter. It is manufactured from animal fats and vegetable oils. It is not as desirable an article of diet as butter. It contains margarine fat and only .5% of the volatile fats, while butter fat contains about 8%.
Oleomargarine may be distinguished from butter by boiling. Butter boils more quietly and a foam is formed on top, while oleomargarine sputters much like oil mixed with water and there is little or no foam produced.
Cheese
Cheese is manufactured from skim milk, whole milk, or milk to which cream has been added. The more cream the richer is the product. Coagulation of the milk is accomplished by adding rennet; the curd is then pressed to expel the whey; next it is placed in molds and kept in a cool place to ripen. After cheese has been properly ripened it makes an excellent article of diet. It contains a large proportion of nitrogenous substances. There are many grades of cheese, the quality depending not only upon the process involved in the manufacturing, but also upon the richness of the milk from which it is made.