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Milk Certification

( Originally Published 1939 )


Principles of certification. The feeding of impure milk to infants has been a potent factor in the incidence of gastrointestinal illness and tuberculosis, and in a high mortality rate. In 1892, a physician of Newark, N. J., Dr. Henry L. Coit, conceived the idea that it was possible to produce cows' milk of a greatly improved quality as compared with that of the ordinary commercial supplies. A plan was formulated to produce such a milk under the direction of physicians. This milk was to be called certified milk because it was approved or certified as having been produced under the most advanced ideas in dairy and medical science. In 1893, Stephen Francisco, of Montclair, N. J., produced the first certified milk for sale, and this performance set a standard of quality which has maintained its pre-eminence.

The certifying group of physicians constitute a committee or "Medical Milk Commission," usually appointed by the state, county, or city medical society. This commission appoints various agents, such as a sanitary inspector, a veterinarian, a physician, and an analyst, to enforce its standards, and enters into a contract with a dairyman whom it considers to have the proper intentions and interest to produce this special milk under their supervision. In 1907, most of the local commissions were organized into the American Association of Medical Milk Commissions for the purpose of unifying certified milk standards and methods, and of extending the work through-out the country. The Association seal may be used by any member while its certification continues. In 1936, there were more than eighty individual commissions comprising the national organization, all working under a single set of regulations. In this respect, certified milk may be said to be the only grade of milk produced and controlled under a nationally uniform code.

Influence on milk-quality standards. The high quality of certified milk soon began to influence the standards of the bulk of the regular milk supply. Health officers and dairymen observed that greater cleanliness and care were possible in the fluid milk industry at large than had previously been the case. When new information became available, the certified-milk industry has been eager and aggressive to apply it to their milk production. In spite of the fact that the quality of the regular milk supply has been steadily rising, the certified-milk people have kept their quality well in advance. Their Research Committee constitutes one of the most aggressive and authoritative organizations of scientists in the dairy industry. The actual amount of certified milk that is consumed constitutes only a relatively small percentage of the total milk consumption, but the influence of the ideals and standards of the certified-milk industry has exercised so salutary an effect on the milk industry in general that its indirect effect is enormous. Many health officers look to this industry to blaze the trail for further advances in dairy husbandry. The great authoritativeness of the pronouncements of their scientific consultants, the high professional standing of their certifying commissions, the personal integrity and financial responsibility of the certified-milk producers, and the sustained superiority of the sanitary and nutritive quality of certified milk have given this industry such a reputation for dependability, excellence, and public service that almost all milk-control laws, ordinances, and regulations not only recognize certified milk as a distinct grade but carry the provision that the rules and regulations of the American Association of Medical Milk Commissions shall be the official requirements for the local production and handling of certified milk.' The legality of such "adoption by reference" is doubted, but it provides the simplest way of incorporating certified-milk methods and standards into local regulations, and is to be preferred wherever possible.

Extent of industry. The high sanitary requirements and the consequent added expense attendant on the production of certified milk necessarily restrict its production to persons who have financial responsibility, a certain idealism and public-health consciousness, and the personal disposition to devote money, time, and attention to a business which seldom pays big dividends. In almost every large community, there is at least one certified-milk producer. In the United States at large, there are about 160 producers. In those communities where this milk is sold, it constitutes about 1 to 10 percent of the total milk consumption, with an average of 1 to 2 percent over the country as a whole. On account of its necessarily higher sales price than that of regular milk, together with the markedly improved quality of the cheaper regular market supplies, the public demand for certified milk has been falling off. This decline is being reduced by the production of special grades of certified milk such as vitamin D, soft curd, and pasteurized, and, in some localities during the past few years, there has actually been an up-trend in the consumption of certified milk.

Operations. The dairyman who would produce certified milk must follow a procedure with the local milk commission very similar to that followed by the ordinary farmer-producer with his health department. He applies to the commission for a contract to produce certified milk. This application is not approved until the premises have been inspected, the employees medically examined, and the cattle given their several tests and found to be in satisfactory health. In addition, the dairyman must secure a milk permit from the local regulatory official.

Medical examination of employees. A medical officer who resides near the certified dairy visits the farm weekly to examine all persons who handle the milk, and all the farm employees and residents who are connected with the milk handling. All new employees must be examined by this officer before assuming their duties. Full report must be made to the commission on blank forms supplied for that purpose. Once a year the attending physician must make a complete examination of all employees. Copies of all reports are to be kept on file at the farm.

Each employee has an examination for: (a) history of enteric fevers; (b) urine and feces cultures for organisms of typhoid, paratyphoid and dysentery; (c) nose and throat cultures for the organisms of diphtheria, septic sore throat, and scarlet fever; (d) Widal agglutination tests. If these examinations disclose no reasons to the contrary, the employee may be allowed to work, and from 30 to 60 days later shall have the feces examination once repeated. Satisfactory evidence must be presented of recent successful vaccination or immunity against smallpox. These examinations are conducted by laboratories and physicians approved by the commission. No person suffering with any communicable disease, and no person recently exposed to such disease, is employed in the production of certified milk. A full record of the names, addresses, employment dates, medical histories, and results of all physical, medical, and laboratory examinations is kept on file on the dairy premises.

The hands of the milkers must be thoroughly washed and scrubbed with soap, running warm water, and brush, and then dried on clean towels immediately before milking. During the handling of the milk, milkers wear clean white suits and caps. While engaged about the dairy, they are not to use tobacco nor intoxicating liquors. They are instructed to keep their fingers away from nose and mouth. No milker is allowed to contact the milk with his fingers or mouth. He may not touch anything but the milking stool, the milk pail, and the cow's teats. No spitting is tolerated.

Toilets are to be sanitary, and not be in proximity to the bottling or receiving rooms. They are to be properly screened, kept clean, and they must be accessible to wash basins, water, nail brush, soap, and clean, individual towels.

Any illness of an employee is sufficient to exclude him from the milk-handling operations until he can be examined by the attending dairy physician.

Health of cattle. Every member of a herd must be tuberculin tested under the Federal-State Accredited Herd Plan, and semi-annually thereafter. All reactors must be immediately removed, the milk discarded, and the stables and yards used by them cleaned and disinfected in a manner approved by the commission,

All cattle producing certified milk must be free from Bang's disease (Brucella infections) as indicated by repeated agglutination tests of their blood serum. Positive reactors must be removed immediately. All herd members must be tested at intervals as determined by ac-crediting authorities.

Any cow affected with mastitis must be removed at once from certified herds, even if only one quarter of the udder is affected, and none of the milk from the other quarters may be used. All three treated cows must be excluded. Cows removed because of disease shall not be returned to the milking herd without the approval of the veterinarian.

Detailed instructions are issued as to how each cow is to be identified. No sick cows, or those suspected of being ill, may remain in a milking herd, nor may cows be permitted to calve in a milking stable. A veterinary inspection shall be made at intervals no greater than a month.

Plant and equipment. There are the usual requirements that buildings are to be located so as to insure good drainage and to be protected from contaminated surroundings. The construction must be of sanitary type. Stables are to have properly constructed manure gutters. Ventilation is to be adequate, and each cow must be allowed 600 cubic feet of air space and 4 square feet of window area. Flies, insects, rats, and other vermin are to be eliminated. Visitors are to be excluded from all rooms in the dairy building where milk, sterilized bottles, or milk-handling equipment is exposed.

The dairy building must not directly connect with the stables or dwelling, and no manure may be piled closer than 600 feet nor on a higher level. The construction must be sanitary, and light and ventilation plentiful. Covered milking pails are preferably to have an elliptical opening 5 by 7 inches in diameter. The top of the pail must be so convex that the entire interior is visible and accessible for cleaning. All milk bottles must be cleansed and actually sterilized so that the final test is freedom from bacteria, chemical reagents, and any other foreign matter. The water supply must be free from contamination as determined by bacteriological examination at least every four months.

Sanitation. The stables must be cleaned twice daily, not less than one hour before milking. Manure must be hauled directly to the fields. The cows themselves must be currycombed, and thoroughly cleaned with a stiff brush or washed with a clean cloth. The udders and flanks must be kept well clipped. Before milking, the udders and teats are to be washed and dried with clean towels. No horses, hogs, dogs, or other animals or fowls are to be allowed to come in contact with the certified herd.

Milk production and handling. The first milk from each teat is rejected. This milk is milked through a fine-mesh strainer or black cloth to indicate whether or not garget is present. If any dirt gets into the pail, the milk is discarded and the pail is washed and sterilized before it is used again. The milk is removed from the stable for straining, and cooled immediately to 50° F. or below.

Bottling is done on the farm where the milk is produced. The cap is applied by a capping machine, and consists of an inner disc and an outer sterile hood which completely covers the lip of the bottle. All milk is delivered to customer within 30 hours from the time of the latest milking.

Permissive pasteurization. Certified milk may be subsequently pasteurized in equipment that is not used for the pasteurization of any other grade of milk. The pasteurization must be done on the farm where the certified milk is produced. It is labeled on the bottle cap with the words "Certified Milk—pasteurized," and is sealed to protect the pouring lip and the neck of the bottle just the same as for the regular unpasteurized certified milk. This milk meets all the requirements of regular raw certified milk, plus the additional requirement of a maximum limit of 500 bacteria per milliliter.

Special types. Certified milk of lower butterfat content than 3.5 is produced under special names as, for example, nursery milk. Some dairies produce certified acidophilus milk, which is a cultured milk discussed in Chapter X. Soft curd certified milk is produced from cows whose milk has been tested by the Hill or an equivalent method to show curd tensions below 30 grams. Vitamin D milk is produced from cows whose milk has been rendered anti-rachitic by means of a supplemental feeding with irradiated yeast of sufficient vitamin D potency to show by a biological assay a content of at least 430 U.S.P. units per quart. (See Chapter X.)

The Rotolactor. This is the name given to a novel and spectacular machine which has been developed at the Plainsboro plant of the Walker-Gordon Laboratories to expedite the production of certified milk on a large scale.' The Rotolactor is a rotary milking unit or slow-motion merry-go-round—a circular platform on which 240 cows are milked per hour. The cows step on and off the platform at the rate of one every 15 seconds, but there is an intervening ride of 121/2 minutes during which the cleaning, foremilking, and milking operations are carried on. The operation is continuous until all the cows have been milked.

This machine makes possible the volume production of clean milk under the most advanced conditions of hygiene and sanitation. The cows are subjected to a series of warm spray washes and showers, followed by drying of the teats and udders with clean, individual towels. In the meantime, all the milking equipment is being sterilized. Within little more than a minute from the time the milk leaves the cow, it has been cooled to delivery temperature. Only four men are possible contacts, namely, a foremilker, two men who attach the teat cups (but who touch the teats scarcely at all), and the attendant at the bottling machine.


Nutritive value. The nutritive excellence of certified milk depends directly upon its food value, and indirectly on its freedom from the products of bacterial metabolism.

In the production of certified milk, it is required that a well-balanced ration shall be fed the herd, adequate in vitamin and mineral content, and all changes of feed shall be made slowly.' As with sanitation and hygiene, certified-milk producers have been alert to the possibilities in improving the nutritional qualities of their product by what may be termed "controlled feeding" of dairy cows and by proper handling of the milk after it is produced. In June, 1937, the American Association of Medical Milk Commissions adopted provisions relating to the enhancement and maintenance of nutritional values in certified milk in recognition of the findings that the nutritional qualities of milk can be significantly influenced by improved methods of feeding cows and of handling milk.

When bacteria multiply in milk, they metabolize mostly the lactose and some of the protein. As long as the milk remains palatable and has not "spoiled," the percentage content of these metabolic by-products is negligible in the reduction of the food value of the milk. But they are not negligible from the standpoint of their effect on the nutrition of the infant. Certified milk, because of its extremely low bacterial content, has undergone less change from their action than any other dairy product.

Epidemiology. In spite of the great care which is exercised in the production of certified milk, several recorded epidemics of disease have been traced directly to this milk. Williams reports an epidemic caused by a carrier of Salmonella schottmülleri (B. paratyphosus B). This milker on the farm had no history of previous illness from this cause. Sixty infants were affected, but none fatally. Williams states that he knows of only one previous outbreak of infectious disease spread by certified milk. This was a diphtheria outbreak that occurred in Westchester County, New York, in 1920.

Armstrong and Parran quote from the Monthly Bulletin of the New Haven Department of Health that an outbreak of septic sore throat traced to certified milk involved 80 cases. A person was ill on the farm for a week before going to the hospital. Pasteurization of the milk checked the outbreak.

On the whole, certified milk has enjoyed a good record of safety. Data compiled by Hardenbergh from the annual reports of the U. S. Public Health Service on milk-borne outbreaks for the years 1923-1935, inclusive, show that, of a total of 564 outbreaks officially reported, only 2 or 0.35 percent were attributed to certified milk, 20 or 3.54 percent to pasteurized milks, and 526 or 93.30 percent to ordinary raw milks. On the assumption that about 2 percent of the milk consumed in the country is certified milk, 49 percent pasteurized milk, and 49 percent ordinary raw milk, then the relative degrees of incidence of these recorded outbreaks for these three kinds of milk will be in the proportions of 1 : 0.4 : 10.7. The number of outbreaks for the certified and pasteurized milks is so small that these incidence factors are substantially the same, indicating that on the basis of these limited figures the two milks have about equally favorable records.


Definition. The U. S. Public Health Service Milk Ordinance de-fines certified milk as follows: "Certified Milk.—Certified milk is milk which conforms with the requirements of the American Association of Medical Milk Commissions in force at the time of production and is produced under the supervision of the Medical Milk Commission of the Medical Society of the county, and of the state board of health or of the city or county health department officer of ." The American Association of Medical Milk Commissions will recognize other properly qualified agencies to supervise the production of certified milk, and will grant them the right to use its copyrighted seal for as long as they continue to comply with its requirements.

Laboratory standards. Bacteriological. Certified milk must be examined bacteriologically at least weekly. The bacteria count must not exceed 10,000 per milliliter, as determined by the special methods and technic of the American Association of Medical Milk Commissions 1 in pasteurized milk, the count must not exceed 500 organisms. In addition, the milk must contain fewer than 10 organisms of the coli group (Escherichia-Aerobacter) per milliliter, and pasteurized certified milk should contain none. Furthermore, the milk must not contain any Streptococcus epidemicus (Davis) organisms.

Chemical. The butterfat content should average 4.0 percent, with a minimum of 3.5 percent, but higher or lower percentages are permissible if declared on the label. The total solids should average not less than 12 percent, and the specific gravity at 60° F. should be not less than 1.029.

Laboratory examination. Physical. These tests are the same as those described in Chapter V, page 93.

Chemical. These tests are the same as those described in Chapter V, page 93.

Bacteriological. Routine bacteriological examination is made for the total count and the presence of hemolytic streptococci by plating 0.1 and 0.01 milliliter of milk on blood agar plates. Certified milk is relatively free from all bacteria other than those which come from the udder, and many of these grow best on blood agar.' The general technic is the same as that used in Standard Methods of Milk Analysis (see page 94) except that the composition of the media is different.

The determination of coliform organisms is made by plating 1 milliliter of milk on desoxycholate agar. Their presence indicates uncleanly milking, contaminated utensils, or the improper handling of milk, either from contamination or lack of proper refrigeration. In pasteurized milk, their presence indicates improper pasteurization or contamination of the milk after it has been pasteurized.

Inasmuch as the milk from healthy cows, produced under clean conditions and protected from subsequent contamination, does not contain bacterial spores, it has become a standard requirement to examine certified milk for the absence of these indications of insanitation. This is the Weinzirl spore test. When milk in test tubes containing petrolatum in incubated, gas formation is indicated by the raising of the plug of petrolatum. A proper quality of certified milk should rarely show gas formation, coagulation, or digestion in any of the tubes.

Control procedure. Inspection of farm. The health record of employees should be examined. All persons who come in contact with the milk or who are employed on the farm should be listed, their medical history checked, and the dates of their physical examinations and the findings recorded.

Records of the tuberculin test of each cow in the herd should be on file at the farm. Each animal should be examined for ear tags or ear marks for identification, and for its full record of the physical examinations, freshening dates, milking record, tuberculin test, and agglutination tests of blood serum for Bang's disease.

The inspection should comprise careful observation of the sanitary condition of the premises, including particularly the removal of the manure, the potability of the water, the sterility of the equipment, the cleanliness of the milking procedure, the promptness of the milk cooling, the proper bottling and capping, and the adequacy of the storage refrigeration.

Examination of samples. Samples should be taken from the original unopened packages which are collected at the plant or from the vehicle of the delivery agent. The samples should be well iced until they are opened in the laboratory for analysis and should be examined within four hours after collection.

An occasional high count does not indicate any serious condition, but, if the counts are high on numerous samples or for several days, they indicate that some condition obtains which should be corrected. In practice, certified milk should be expected to average materially less than 5000 organisms per milliliter, and many farms operate on an average of less than 1000 per milliliter. Brown shows 6 that the arithmetical average of a series of bacterial counts is not nearly so significant of good sanitary practices as a "uniformity rating." The uniformity rating is the ratio between the logarithmic average and the arithmetical average. If a milk was perfectly uniform by all its samples having less than the legal bacterial limit, this ratio would be 1.0. The compliance rating gives the percentage of the number of samples that fall within the legal limits.

If any samples are found to contain Streptococcus epidemicus, the milk from each cow should be plated for this organism so that the infected animal can be identified and removed from the herd immediately.

If any lapse in the regulations is discovered, a violation notice must be left with the proprietor and a date given for its correction and full compliance. If any of the cattle or workmen are found to have developed a communicable disease, the health officer should order the immediate pasteurization of the entire supply until further inspection shows that the emergency no longer exists.


1. Methods and Standards for the Production of Certified Milk, May 12, 1936. Am. Assoc. Medical Milk Commissions, Inc., New York. (a) p. 19; (b) p. 17; (c) p. 18.

2. J. G. HARDENRERGII, Am. J. Pub. Health, 25, 959 (1935); see also J. Am. Med. Assoc., 105, 601 (1935).

3. H. WILLIAMS, J. Am. Med. Assoc.. 84, 251 (1925).

4. C ARMSTRONG and T. PARRAN, JR., Pub. Health Repts. Su l. 62, 1927.

5. J. G. HARDENRERGM, 21st Ann. Rept. Internat. Assoc- Dairy and Milk Inspectors, 1933.

6. J. H. BRowu, Am. J. Pub. Health, 28, 1053 (1938).

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