THE BACTERIOLOGY OF ICE CREAM 191 



water should be circulated or the freezer slowly cooled in 

 some other way before the cold brine is circulated. 



Employees. The direct contamination of dairy products 

 from persons is especially undesirable because of the possibility 

 of the introduction of pathogenic bacteria in this way. The 

 real danger from employees is shown by several typhoid epi- 

 demics in which the ice cream causing the infection was con- 

 taminated by carriers coming in contact with the material 

 during the manufacturing process. The handling of the cream 

 after pasteurization should be done under the most careful 

 conditions, as should also the handling of the materials that 

 are not heated at all. 



CHANGES IN THE NUMBERS OF BACTERIA DURING FREEZING, 

 HARDENING, AND HOLDING 



The changes in the numbers of bacteria during the freezing, 

 hardening and holding of the ice cream are of considerable 

 importance if bacterial standards for this product are to be 

 employed. 



In the modern ice cream freezers, the ice cream mix is sub- 

 jected to rather violent agitation in addition to having its 

 temperature brought down below the freezing point of water 

 and it would be expected that significant changes in the num- 

 bers of bacteria, as determined by the plate method, might 

 occur. The lowering of the temperature would be expected 

 to destroy certain of the bacteria while the agitation would 

 be expected to break up the clumps of bacteria that might be 

 present. The Iowa Agricultural Experiment Station 14 com- 

 pared the bacterial content, as determined by the plate method, 

 of the ice cream mix and the frozen ice cream in 51 cases. In 

 2 cases (4 per cent) there was no change; in 6 cases (11.8 per 

 cent) the freezing lowered the count, the decrease varying 

 from 2 to 31 per cent (Av. 13.0 per cent) while in 43 cases 

 (84.o per cent) it increased the count from 2 to 227 per cent 

 ( Av. 46.3 per cent) . A few representative comparisons follow : 



Unpublished data. 



