39° 



MICROBIOLOGY OF MILK AND MILK PRODUCTS 



cream as they come from the machine will normally show larger 

 bacterial counts in agar and gelatin plates than will the milk before 

 treatment, due of course to the breaking up of colonies. The usual 

 effect upon the germ content of passing milk through a separator or 

 clarifier may be seen in the following tables: 



Effect of a Centrifugal Clarifier upon the Germ Content of Milk 



These increased counts do not mean that there is an actual in- 

 crease in individual bacteria in these samples due to the action of 

 the separator or clarifier. What it does mean is that the small clus- 

 ters or groups of organisms, as they exist in the whole milk are thrown 

 apart by the centrifugal force and therefore develop individual colonies 

 in the plate cultures. 



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 kjiows that it spoils 

 very quickly if allowed ' to stand at warm temperatures. If, howr 

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

 quality of the milk 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 



