High bacterial counts in milk are most fre quently due to growth of the organisms in the milk if it is not promptly cooled at least to 50° F. Bacteria multiply rapidly at temperatures above 50° F. and in general the higher the tempera ture the faster they grow up to 100° F. Milk immediately after production should therefore be cooled quickly and kept cold.
Pasteurisation.-- Since pathogenic bacteria may be present in milk it is a common prac tice to heat it to temperatures above 140' F. This process is known as pasteuriza tion. From a sanitary standpoint pasteurization is of greatest value when market milk is under consideration. The pasteurization of milk, when the process is properly performed, de stroys the organisms which cause typhoid fever, diphtheria, septic sore throat and tery, and offers protection against the and-mouth disease. From an economic stand point, pasteurization is of value because it in creases the keeping quality of milk and pre vents financial losses by souring. As practised at present, pasteurization destroys about 99 per cent of the bacteria present in milk, including all disease-producing organisms.
' Three processes are commonly used in this country: The first is known as the flash, or Continuous process; the second as the holder or holding process; and the third as pasteuriza tion in the bottle. The flash process consists in heating the milk rapidly, usually to 160° F. or above and then cooling quickly. The heating in this process requires only from 30 seconds to one minute. In the holder process the milk is heated to from 145° to 150° F. and held for 30 minutes before being cooled. This is the most commonly used process and is superior to the flash process in every way. Pasteurization in the bottle is one of the latest developments in the process to be used on a practical scale. In this process the milk is bottled, then heated in the bottles to from 145° to 150° F., then held for 30 min utes before being cooled. In any method of pasteurization the milk after heating is cooled as rapidly as possible to 50° F., and lower when possible.
The temperature recommended for pasteur ization is 145° F. for a period of 30 min utes. This temperature and period of hold ing is the most desirable (1) because it is high enough to destroy pathogenic bacteria; (2) be cause it leaves in the milk a maximum num ber of lactic-acid-producing bacteria which cause the milk to sour in a more or less normal manner, although the souring is delayed; (3) because the milk does not undergo any appre ciable chemical change; (4) because it has little or no effect on the flavor or on the cream line of milk; and (5) because of the economic ad vantage of not having to heat the milk to higher temperatures, thereby saving in heating and consequently in cooling.
Cream is pasteurized by the same method as milk, and usually the viscosity of the cream is somewhat reduced. This is particularly true in high-temperature pasteurization. The early ob jections to pasteurization have been shown by scientific investigation not to be valid, so that the pasteurization of milk and cream is now ex tensively and in fact very generally practised. It is even, compulsory in a large number of cities.
Milk should be produced and handled in such a manner as to keep bacterial contamination as low as possible and prevent subsequent growth. The practical way of accomplishing this is to observe the utmost cleanliness in all stages of production, to cool the milk to at least 50° F. promptly after it is drawn and to hold it continuously at such low temperature. As pathogenic or disease-producing bacteria are the most dangerous of all forms ever found in milk, special care should be taken to exclude them. For this purpose, it is necessary to give close attention to the health of the am mals and all persons having to do with the herd or the milk. Some serious outbreaks of dis ease have been due to the handling of milk by persons suffering only mildly with a contagious disease such as typhoid fever or who have been exposed to the disease. Dairy cows should be examined at least twice every year by a com petent veterinarian; some of the best dairies have examinations more often. The milk of a cow suspected of being out of condition or not in good health should not be used. Many bac
teria that enter milk are carried by small parti cles of foreign matter such as manure, dust, dirt, hairs, etc. Of course, these are most abundant in ill-kept barns, where milkers as well as the cows and their surroundings• are al lowed to be unclean. Barns should be kept thoroughly clean. The use of pine shavings for bedding contributes much to cleanliness and they are now found in many of the best dairies. Barns should be so constructed and the work should be so planned that there would be no occasion for unnecessary dust in the atmos phere at the time of milking. Mitch cows should be 'groomed" frequently and udders should always he cleaned just before milking with a damp cloth. Mincing should be done quietly. Freeman has shown that the milk drawn by a man who agitates the udder vio lently may contain 10 times as many bacteria as that drawn by a quiet milker. Milk should not be used until it becomes normal after calv ing. In addition to being in good health and avoiding exposure to contagion, the attendants in a dairy should be personally clean. A spe cial clean suit should be put on and hands should always be thoroughly cleaned before milking. The practice of 'wets milking is ex tremely filthy. All dairy utensils should be sim ply constructed and easily cleanable. They should not be made of any open or porous ma terial such as wood. Immediately after use they should be cleaned and then sterilized for five minutes with steam. Milk should be promptly removed from the stable, strained, cooled and cold-stored. It should be handled in a room specially fitted for the purpose clean and light. A good form of strainer is provided with a double thickness of sterile cheese-cloth filled between with pure white sterile cotton. The cloth and cotton should be changed as often as they commence to show dirt near the lower surface. The usual cool ing device consists of an apparatus made of thin metal and so arranged that cold water is on one side while the milk being cooled passes over the other. With certain forms of coolers, it is found entirely practicable to reduce the temperature of the milk quickly to within 2 to 4 degrees of the temperature of the water. After cooling, milk should be placed in cans or jars, as may be required and held at a low tem perature continuously until used. • When milk is to be used for butter and cheese making it is also necessary for it to be held at low tem peratures to prevent undesirable fermentations_ Items that need to be kept in mind and con ditions which should be observed in the man agement of a first-class dairy are summarized in 'Twenty Dairy issued by the United States Department of Agriculture, as follows: ma cows 1. Have the herd examined at least twice a year by a skilled veterinarian. Promptly remove animals suspected of being in bad health. Never add an animal to the herd until certain it is free from disease, particularly tuberculosis.
2. Never allow a cow to be excited by fast driving, abuse. loud talking, or unnecessary disturbance; do not expose her to cold or storms more than necessary.
3. Clean the entire body of the cow daily; hair in the region of the udder should be kept short by clipping.
4. Do not allow any strong-flavored food, like garlic, cabbage or turnips, to be eaten except immediately after milking Changes in feed should be made gradually.
S. Provide fresh pure water in abundance, easy of access and not too cold.
ma STAHL= 6. Dairy cattle should be kept in a stable. preferably without ? or 'tome loft, and where no other animals are housed.
7. The stable should be light (4 square feet of glass per cow) and dry, with at least 500 cubic feet of air space per animal. It should have air inlets and outlets, so arranged as to give good ventilation without drafts of an on cows.
8. The floor should be tight and constructed preferably of cement; alls and ceilings should be tight, clean, free from cobwebs and whitewashed twice a year. Nave as few dust-catching ledges, projections and corners as possible.
9. Allow no dusty. musty, or dirty litter, or strong. smelling material in the stable. Haul manure to field daily, or store under cover at least 40 feet from stable. Use Iliad plaster daily in gutter and on floor.