458 



MICROBIOLOGY OF MILK AND MILK PRODUCTS 



TEMPERATURE. The temperature at which milk is kept is one of 

 the most important factors determining the development of its micro- 

 bial content. Every one at all familiar with milk knows that it spoils 

 very quickly if allowed to stand at warm temperatures. If, how- 

 ever, the milk is held at temperatures of 10 or lower, its keeping 

 quality is greatly increased. Most of the ordinary species of organisms 

 which gain entrance to milk do not grow rapidly at temperatures 

 of 10 or lower. There are, however, certain species which will 

 grow with considerable rapidity at temperatures below 10. especially 

 some of the spore-bearing non-acid forms. If the temperature of the 

 milk is allowed to rise above 10, the growth of the common species 

 increases rapidly. The influence of temperature upon the develop- 

 ment of bacteria may be seen in the following experiment where 

 a given lot of milk was thoroughly mixed and divided into seven 

 portions, which were then held at the temperatures indicated for 

 twelve hours, at the end of which time they were plated for the 

 total germ content. 



EFFECT OF DIFFERENT TEMPERATURES UPON THE DEVELOPMENT OF BACTERIA 



IN MILK 



The fresh milk showed a count of 5,000 per c.c. and curdled in 

 fifty- two hours at a temperature of 21. The curdling time of these 

 samples was determined by placing them at a constant temperature 

 of 21 at the close of the twelve-hour period and holding them at this 

 temperature until coagulation took place. The difference in time of 

 curdling .therefore is due to the maintenance of the special tempera- 

 ture for twelve hours only and not for the entire period up to the time 

 of curdling. 



