WHAT IS MEANT BY "QUALITY" IN MILK.* R. S. BREED, H. A. HARDING, W. A. STOCKING, JR., INTRODUCTION. Milk is often called good or bad, but it is difficult to define either quality. It needs but a slight study of the milk question to recognize that the goodness or badness of milk depends upon several factors. Because of the complexity of this situation there is much confusion in the public thought regarding quality in milk. As a result, milk is still commonly sold without the use of grades to designate quality, the State of New York being one of the few exceptions to this rule. The present publication is a brief summary of previous considerations of the various sides of this question, a plea for a broader consideration of the problem of milk quality, and a suggestion regarding the line along which future progress in the improvement of city milk supplies will undoubtedly be made. ELEMENTS OF QUALITY IN CITY MILK. Many factors combine to determine the quality of milk. Each of the factors has been recognized as important at one time or another, but apparently thus far no one has succeeded in so fully analyzing the city milk situation as to formulate a complete expression for milk quality. The following summary1 of the elements of quality in city milk under the headings of food value, healthfulness, cleanliness, and keeping quality is an attempt at such an analysis. The order of presentation of these elements is essentially that in which they have been previously brought to public attention. 1 This summary of elements of quality in city milk does not consider the occasional occurrence in milk of disagreeable substances, of which onions and gasoline are the most common examples, because the evident presence of such substances automatically excludes such milk from the city trade. Reprint of Bulletin No. 438, October, 1917. FOOD VALUE. While milk is sometimes used as a beverage, the fundamental reason for the existence of the present vast traffic in milk is the fact that milk is one of our most important foods. Not only does it offer energy in a readily available form, but the amount and variety of the compounds contained in milk make it a peculiarly valuable food for growing children. The present consumption of milk in this country is only about 0.6 pint per capita per day, altho from the standpoint of protein, which is especially needed by the growing child, or from the standpoint of total energy as utilized by the adult, much more food value is obtainable from milk for a given sum of money than can be purchased in any comparable food. The high food value of milk is shown by the following table recently prepared by the U. S. Department of Agriculture: PROTEIN 1 quart of milk is equal to: 6 ounces of round steak 8.5 ounces of fowl ENERGY 1 quart of milk is equal to: 10.7 ounces of fowl In 1856 the laws of Massachusetts2 attempted to protect milk from adulteration and since that time federal, state, and municipal authorities have enacted laws establishing standards for butter fat and the other solids in milk. It was the original conception that milk is of essentially fixed composition and that the establishment of minimum standards would stop the watering and skimming of milk. The establishment of these legal standards undoubtedly has had a pronounced effect in limiting open and gross adulteration of milk, but the secondary and unexpected effects of such enactments have been such as to raise the question whether, taken as a whole, they have been beneficial to the quality of the milk supply. While it is true that these legal standards set definite limits to the extent to which the food value of milk could be reduced without incurring the penalty of the law, at the same time they offered indirectly a stimulus for the reduction of such food value to a figure approximating these legal minimum standards. 2 Parker, H. N. City Milk Supply, p. 370. 1917. The cost of producing milk at the farm is fairly proportional to the amount of food value in the milk. With the narrow margin of profit which exists in milk production, there has been a strong impelling force toward the production of milk with the smallest food value that the market would accept without reduction in price. When the law prohibited the reduction of food value by the direct addition of water, the same result was frequently accomplished by the selection of animals producing milk which approached or even fell below the legal minimum limits. It is a matter of common knowledge that the milk supplies of our larger cities have been falling in food value, and today much of the milk sold in such cities is almost exactly at the legal limit of fat and below the legal limit in solids not fat. This reduction in food value is all the more striking in view of the marked preference which the consuming public has for milk of high food value. Many progressive milk dealers, recognizing this situation, have offered milk high in fat content at an advanced price. with commercial success. While there is no simple, and at the same time, entirely satisfactory method of expressing the food value of milk, it may be roughly measured in a variety of ways. The housewife customarily judges the food value of milk by noting the depth of the cream line in the milk bottle. The food values of the other constituents of normal milk do not vary in absolute proportion to the fat, and therefore the fat is not an entirely accurate measure of the food value of the milk; but, at the same time, the variations in total food value are so nearly proportional to the variations in the fat of the milk that the fat content. of milk of cows may well be used as an index of the relative food value of various samples of milk. This index has the added convenience of being easily and accurately determined by means of the Babcock test. HEALTHFULNESS. It is not enough that a bottle of milk shall have abundant cream in order to be accurately characterized as good milk. If such milk should contain even a limited number of virulent typhoid-fever organisms, it would be rejected by anyone who was acquainted with this fact. While the milk business is conducted primarily because milk is a valuable food, the occasional appearance of an epidemic spread by the use of milk has made the public suspicious of the healthfulness of all milk. This public suspicion is a severe handicap to the milk business, and any procedure which will remove this suspicion and stimulate the increased consumption of milk will be of great economic benefit to the dairy industry as well as to the consumer. 4 While the possibility of milk functioning as a carrier of disease had been previously discussed, beginning about 18933 the use of the tuberculin test revealed a large amount of tuberculosis in dairy cattle and the public was impressed with the danger of spreading tuberculosis thru the milk. Later investigations, particularly those made during the past fifteen years, have fully demonstrated the danger of tuberculosis being transmitted from cows to children thru the milk. Occasional epidemics of septic sore throat and typhoid fever and less frequently epidemics of scarlet fever and diphtheria transmitted in the same way have given good grounds for suspicion regarding the healthfulness of the ordinary raw milk supply. The amount of danger from this source is commonly overestimated, but its existence, particularly in the case of children, is beyond question and should not be overlooked. 5 Health authorities, early recognizing tuberculosis of cattle as a public menace, attempted to stamp it out by the widespread application of the tuberculin test. The difficulties encountered in such an attempt made it evident that whatever may be the value of the tuberculin test as such, there is little prospect that the application of the test will become so widespread as to offer protection to the general milk supply. It has also been recognized that tuberculosis is only one of a number of diseases which may be distributed thru the milk supply. Any plan which is to make milk a safe article of food must take account, 3 Pearson, L. A. Proceedings of the First International Veterinary Congress of America. Oct., 1913. 4 Park, W. H., and Krumwiede, C. The Relative Importance of the Bovine and Human Types of Tubercle Bacilli in the Different Forms of Tuberculosis. Collected Studies from the Research Laboratories, Department of Health, New York City, 7: 88-92. 1913. 5 Trask, J. W. Milk as a Cause of Epidemics of Typhoid Fever, Scarlet Fever, and Diphtheria. Public Health and Marine Hospital Service of the United States, Hygienic Laboratory Bul. 56, pp. 23-149. 1909. Kelley, Eugene R. The Quantitative Relationship of Milk-borne Infection in the Transmission of Human Communicable Diseases. Jour. Am. Med. Assoc. 67: 1997-1999. 1916. not only of diseases which may be transmitted from the cow, but also of the more formidable list of diseases which may be transmitted by the milk from the people who handle it to those who consume it. The history of certified milk has made it evident that a careful medical supervision of both animals and men will reasonably protect the milk from danger of transmitting human diseases, but the expense of such supervision is large. Pasteurization of milk was early advocated as a means of safeguarding the consumer from the dangers, not only of tuberculosis, but of other transmissible diseases. As with the tuberculin test, so with pasteurization, many practical difficulties were encountered in applying the process to the milk supply. The studies of Theobald Smith and of Russell and Hastings7 which pointed out the practicability of pasteurizing milk at 140° F. for thirty minutes, mark the real beginning of modern successful milk pasteurization. This pasteurization, which both gives the desired protection against disease germs and furnishes a product satisfactory to commercial milk requirements, was the beginning of a widespread general interest in the subject. This interest has grown to the point where the regulations of the largest cities and of some of the smaller cities make such pasteurization of the general milk supply compulsory. In some instances this movement toward pasteurization has even taken the form of state enactment.8 It is evident that if the milk supply is to be made so safe as to banish the suspicion of danger from disease germs, which is now a factor limiting the consumption of milk, the milk must either be produced under a careful medical supervision regarding the health of the cows and men or it must be properly pasteurized. CLEANLINESS. In order to conform to the general opinion of a good milk, it is not sufficient that a milk shall have high food value and shall be 6 Smith, Theobald. The Thermal Death-Point of Tubercle Bacilli in Milk and Some Other Fluids. Jour. Exp. Med. 4: 217-233. 1899. 7 Russell, H. L., and Hastings, E. G. Thermal Death Point of Tubercle Bacilli under Commercial Conditions. Wis. Agr. Exp. Sta. Ann. Rpt., 17, pp. 147-170. 1900. 8 California St. Bd. of Health. Special Bul. 13. 1916. Oregon Dairy and Food Bul. 5, p. 2. 1917. |