(b) The holding process: The milk is heated in large vats and the temperature maintained for some time (Fig. 59). The temperature used is sufficient to kill pathogenic organisms. At the completion of the process the hot milk is cooled by running over cooling coils and then bottled (Fig. 56). The process will efficiently destroy infective agents present, but the milk may be subsequently contaminated.
(c) The in-bottle method, which is a modification of the holding process. The milk is run into clean bottles, the bottles capped with crown seals and submerged in vats of water which are heated to the desired temperature and this temperature maintained, or they are placed in closed chambers and sprayed with hot water. Various commercial modifications of the pro cedure are in vogue (Figs. 6o, 61). After heating the bottles are cooled and chilled. This method possesses the advantage that subsequent contamination is prevented.
The most satisfactory pasteurization from a hygienic stand point is achieved by holding the milk from 35 to 4o minutes at a temperature of 65 degrees C. (Fig. 58). Pasteurization does not alter the digestibility of the milk; though some may observe a difference in its palatability. The heating alters the vis cosity of the butter-fat, so that a distinct cream line is not formed. Oxidases and vitamines are destroyed, so that teurized milk used for infant feeding should be supplemented with orange juice to supply vitamines, otherwise some children may develop infantile scurvy. Pasteurized milk must be cooled and carefully kept cool, otherwise it is apt to putrify instead of souring, due to the destruction of the lactic ferments, while the spore forming proteolytic bacteria survive the heating. To secure the maximum protection, all pasteurizing vats should be equipped with recording thermometers, and the process should be carried out under official supervision.
2. By another classification milk may be divided into three grades: (a) Certified milk.
(b) Inspected milk.
(c) Market milk.
The use of the term certified, as applied to milk, is limited to milk produced in accordance with the requirements of the American Association of Medical Milk Commissions. For its production, the dairyman enters into a contract with the association, agreeing to the following conditions, in return for which his milk is certified.
(a) The producing dairies shall be periodically inspected.
(b) Frequent analysis of the milk shall be made.
(c) Pure water shall be supplied for dairy use.
(d) The dairy herd shall be free from tuberculosis as demon strated by frequent inspections and tuberculin tests. In addi
tion all cows shall be free from other diseases liable to cause deterioration of milk.
(e) The stables must be kept clean and be properly ventilated and lighted.
(f) The cows must be properly fed and cared for.
(g) All milk handlers must be free from communicable dis eases. They must observe scrupulous cleanliness in their work (Fig. 53).
(h) All care must be used in milking, the milk must be promptly cooled, placed in sterile bottles and stored at so de grees F. or lower until delivered (Fig. so).
(i) A bacterial count not in excess of To,000 per c.c. is per mitted and the milk must not be over 24 hours old when delivered.
Certified milk represents the highest grade of milk obtainable. Its careful production makes it well adapted to infant feeding.
The term inspected milk is applied to a very good grade of raw milk, however not as reliable as the certified grade. It is applied to clean, fresh milk from healthy cows which are tuber culin tested and examined by a veterinarian. The cows are fed, watered, housed and milked under good conditions, but not necessarily equal to those required for certified milk.
Scrupulous cleanliness must be used in milking and care taken to prevent persons having communicable disease coming in con tact with the milk. It should be placed in sterile bottles and stored at so degrees F. A bacterial count of not over ioo,000 bacteria per c.c. is permissible.
The term market milk is applied to all milk not certified or inspected in accordance with the above definitions, and to all milk of unknown origin. Common sense indicates the neces sity for the pasteurization of all milk of this grade.
5. Dairy in the hygienic quality of milk can best be accomplished by supervision of the condi tions under which milk is produced and handled. Results are accomplished along two lines (I) by the enforcement of regula tions designed to secure proper conditions and methods, and (2) the education of dairymen along the lines of hygienic milk production. There can be no doubt that markedly bene ficial results follow the introduction of efficient systems of in spection by tactful inspectors. On the other hand, inspection will not cure all of the evils or absolutely safeguard the milk supply. Inspection requires that all sources of supply be examined, hence in order that they may be known to the authorities a system of liscensure is necessary. Inspections are of the greatest value when a fixed routine is followed in making the inspections. To this end score cards are of great value.