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Fermented Milk

( Originally Published 1939 )


Acidophilus milk. The successful production of acidophilus milk is a difficult commercial undertaking because it is dependent on the use of the best bacteriological and operating room technic.' As the culture seems to lose its potency with time, fresh strains must be isolated from rat or human feces every few months. The milk for carrying the cultures is sterilized under pressure so that it has a slightly caramelized color. It is inoculated with antiseptic care, and incubated at 98-100 F. until the milk has curdled. This culture, known as the mother starter, is maintained by daily transfers from flask to flask.

The bulk starter (used to inoculate the large batch of milk in quantity production) is prepared in large sterile flasks with all the care exercised for laboratory propagation.

The batch of milk must be of the best quality. Ordinarily skimmed milk is used. It is heated near the boiling point for an hour or more to make it as nearly sterile as practicable, and cooled with great care to prevent contamination. After inoculation, it is incubated at about 98 to 100 F. (or similar temperature according to the nature of the culture) for about 18 to 24 hours until the curd has mildly set. This is broken by gentle stirring, cooled, and bottled. Acidophilus milk should contain several hundred million acidophilus organisms per milliliter. These will die off unless the milk is kept at room temperature. Kulp showed that the count will be maintained for several days at 5 C. (41 F.), but that if it is to be held longer it must have no more than a very low contamination and be stored within a temperature range of 12 C. (54 F.) and 16 C. (61 F.), provided that the acidity is 0.65 percent.

Acidophilus milk is covered by U. S. Patent 1,506,501, August 26, 1924, issued to Rettger and Cheplin, to prevent its unscrupulous exploitation. No effort has been made by the inventors to prevent the public from making and using acidophilus milk.

Buttermilk. Buttermilk is the fat-free milk which remains in the churn after the butterfat has been churned out. It may look and taste like ordinary skimmed milk if made from the churning of sweet cream, or it may be sour if churned from cultured cream. Sometimes small granules of butter may be present. The increasing consumer demand for buttermilk has outstripped the production capacity of the churning operations of the milk distributors in the large population centers. This has led to the substituting of what is called cultured buttermilk. In natural buttermilk, the acidity has coagulated the casein into fine particles which will settle out on standing, but in the cultured product a viscosity is imparted to prevent this separation.

Although it is possible to sour milk by letting it stand exposed to the air, a starter culture is used to insure a controlled fermentation. No particular organism has found general favor as yet, although good starters must produce lactic acid and whatever accompanying aroma and flavor are desired.

In commercial plant practice, an excellent quality of milk is heated near boiling for an hour, cooled, and inoculated with the culture. Propagation and maintenance of the culture are effected by daily transfers to freshly steamed and cooled milk. This mother starter is used to inoculate the larger amounts (about 50 gallons) of the bulk milk. Preferably, this milk is pasteurized at 180 F. for 30 minutes, cooled to about 70 F., and then inoculated with the mother culture, incubated overnight to the desired degree of taste and flavor, and finally cooled. The curd is broken to a fine, smooth consistency, and the milk is bottled. Sometimes gelatin may be used to prevent wheying off.

Flavor can be improved and butter granules can be suspended by spraying melted butter into the batch, or by churning the cream until butter just begins to come and then adding the entire contents of the churn to the batch of cultured skim milk.

Other fermented or soured dairy products are kefir, kumiss (kumys, koomiss), yogurt (yoghurt), sour cream, and different cultured butter-milks, but their sale in the United States is relatively limited.

The U. S. Department of Agriculture has defined buttermilk as follows:

Buttermilk. The product that remains when fat is removed from milk or cream, sweet or sour, in the process of churning. It contains not less than 8.5 percent of milk solids not fat.

Cultured Buttermilk. The product obtained by souring pasteurized skimmed or partially skimmed milk by means of a suitable culture of lactic bacteria. It contains not less than 8.5 percent of milk solids not fat.

Numerous commercial laboratories sell lactic cultures of different

types for making cultured buttermilk, but the sources of acidophilus culture of authentic origin or therapeutic effectiveness are very few.

In order to provide a source of cultures of unquestioned potency and reliability, the National Acidophilus Milk Cooperative Association, 270 Broadway, New York City, provides a culture and control service for its member companies.

Epidemiology. In general, the titratable acidity of the sour or fermented milks such as buttermilk, acidophilus milk, bulgaricus milk, and yogurt ranges from about 0.9-1.2 percent as lactic acid. This relatively high acid precludes the proliferation of pathogenic organisms. It is probably because of this fact that epidemics of communicable disease have not been traced to these milk products. If they should become infected, their high acidity would cause the pathogenic organisms to die off.

Therapeutic effects. Several types of fermented milk have long been used in the East as articles of food or as beverages. The purpose of the fermentation was to preserve the milk or to improve its taste (or effect). However, Metchnikoff established a sour-milk therapy when he and his associates published data to show that a milk soured by Lactobacillus bulgaricus possessed properties peculiarly beneficial to the prolongation of human life and the postponement of senility. His reasoning was based on the observation that Balkan peasants who consumed large amounts of this sour milk were conspicuous for longevity.

It was thought that this longevity was induced by the implantation of these acid-forming organisms in the intestine, thereby preventing the development of putrefactive organisms whose harmful metabolic by-products were absorbed by the system. Many people bought this Bulgarian buttermilk, as it was sometimes called. Rogers's review of the literature 1 shows that these expectations were not realized.

The literature on Lactobacillus acidophilus has been reviewed up to 1931 by Frost and Hankinson.

Rettger and his associates 8 have shown that intestinal hygiene can be improved if conditions can be induced in the intestinal tract suitable for the proliferation of the aciduric organisms of Lactobacillus acidophilus. They showed that, when lactose (or milk) is fed in substantial amounts, the fecal flora undergoes a change, so that the originally few Lactobacillus acidophilus bacteria can outgrow and counteract the mixed flora of putrefactive organisms and thereby prevent the formation of the nitrogenous decomposition products which are believed to induce senility and to shorten life. The work of Rettger and his students, especially Cheplin, Kopeloff, and Kulp, has been confirmed and extended. Rettger and associates 9 report favorable results in the treatment of simple constipation, constipation accompanied with biliary symptoms, mucous colitis, and chronic ulcerative colitis. About two-thirds of their cases responded favorably to this dietary regimen, especially when feeding periods of 8 to 12 weeks were alternated by rest periods of 4 to 6 weeks, until implantation of the acidophilus organisms had been effected. For some individuals several such cycles were necessary to secure persistent implantation.

In another series, 22 of a group of 27 children, ranging in age from 10 months to 13 years, were completely relieved of intestinal stasis by the use of acidophilus milk. It forms a very fine curd which digests with ease.

Stark and his associates studied the therapeutic effect of drinking acidophilus milk by examining the feces of 56 constipated persons and 58 normal ones over a period of 18 months. During the feeding period, the number of these organisms in the feces increased enormously but soon disappeared after the milk was withdrawn. In general, the types of bacteria were only slightly changed, but the significant discovery was made that the amount of indole definitely decreased. The feces of all the patients contained more moisture. Of the constipated group, 67 percent reported definite improvement, and the non-constipated group- reported that they were in better physical condition while they were drinking acidophilus milk.

Unpublished work of the Sealtest System Laboratories showed that about two-thirds of a group of more than 100 persons, who suffered to some degree from what they called "constipation," were benefited or relieved after drinking acidophilus milk for several weeks at the daily rate of 1 pint per person.

Rettger's school holds that Lactobacillus acidophilus is the normal inhabitant of the intestinal tract, and that when these organisms are fed in large numbers, particularly when lactose is a large part of the diet, they will proliferate, will transform the intestinal flora into a predominantly aciduric one, and will remain implanted after the treatment has been discontinued. His ideas have not been accepted in many quarters, largely because enthusiasts and some commercial concerns have made extravagant claims and have marketed various kinds of acidophilus therapeutic preparations of indifferent potency.

Ordinary buttermilk has not been shown to have any therapeutic action simulating that of acidophilus milk. Its content of lactic acid bacteria is no more potent than the bulgaricus organisms.

Food value. The food value of the fermented milks does not differ greatly from that of skimmed milk. Most of them have Iittle or no butterfat. A large part of the lactose has been converted into lactic acid. However, this acid and the remaining carbohydrate are avail-able, together with all the original proteins and minerals. The finely divided or incipient coagulation of the protein greatly improves its digestibility and renders it especially useful in certain gastric disturbances when scarcely any food can be tolerated. Its sharp taste and possibly the carbon dioxide aid its palatability and stimulate its digestion respectively.


Chemical. The butterfat content and the acidity of buttermilk and acidophilus milk are determined by the same methods as are employed for milk (see page 94).

Bacteriological. Bacteriological examination includes identification of the predominating organisms present and determination of the number of living cells of this type and the extent of contamination with foreign strains.

There is difference of opinion as to the therapeutic effectiveness of the rough filamentous (fuzzy) X type as compared with the smooth dense Y type. The X type are isolated from the intestines and stools of infants; the Y type are found in the mouth and on cereal grains and also as dissociates of the X type. Platings are prepared on dilutions up to 1-1,000,000 on modified tomato agar (or other special media), and the plates are incubated inverted under an atmosphere containing 10 percent CO2 at 37 C. for 14 days. Gram-stained smears of lactobacilli are all Gram-positive, non-sporulating rods. Gram-stained smears are prepared from tubes of milk inoculated with characteristic colonies, and compared with those from the sample.

Contamination with other types of bacteria can be determined by plating the sample on nutrient agar, incubating aerobically for 10 days, and then counting all colonies.


1. L. A. RocERS, U. S. Dept. Agr. Bul. 319, revised, November, 1928.

2. W. S. KuLe, Am. J. Pub. Health, 21, 873 (1931).

3. Associates of Remits, Fundamentals of Dairy Science, Reinhold Publishing Corp., 2d ed., New York, 1935, pp. 35, 38, and M. A. BRIDGES, Food and Beverage Analyses, 2d ed. Lea & Febiger, Philadelphia, 1935.

4. Service and Regulatory Announcements, Food and Drug 2, fifth revision, November, 1936.

5. W. D. FROST and H. HANKJNSON, Davis-Greene Corpn., Milton, Wis., 1931.

6. L. F. RETrGER and H. A. CHEPLIN, A Treatise on the Transformation of the Intestinal Flora, Yale University Press, New Haven, Conn. 1921.

7. M. KOPELOFF, Lactobacillus Acidophilus. Williams & Wilkins Co., Baltimore, 1925.

8. W. D. FRosr, T. H. BUTTERWORTIH, and S. M. FARR, Am. J. Pub. Health, 21, 862 (1931).

9. L. F. RETTGER and associates, Lactobacillus and Its Therapeutic Application, Yale University Press, New Haven, Conn., 1935.

10. L. F. RETTGER, L. WEINSTEIN, M. BOGIN, and J. E. WEISS, Am. J. Digestive Diseases Nutrition, 5, 170 (1938).

11. C. N. STARK and associates, Am. J. Pub. Health, 24, 470 (1934).

12. Amer. Pub. Health Assoc. Year Book, 1937-8, p. 56.

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