8 MASS. EXPERIMENT STATION BULLETIN 314 



ever, where pasteurized mixes were recontaminated with lactic acid organisms 

 after cooling to 68° F., it was found that the bacterial count increased as much as 

 600 per cent when these mixes were held for 6 hours at 68° F., as compared with 

 identical mixes held for 6 hours at 38° F. Therefore, in all probability, a pasteur- 

 ized mix recontaminated after cooling would show a marked increase in bacteria 

 after being held 6 hours at 68° F. This point should not be considered an objec- 

 tion to short-time aging at 68° F., as it is not good practice in ice cream making 

 to permit recontamination of the mix after pasteurization. 



In a previous study (3) it was shown that by aging ice cream mixes for 4 hours 

 at 68° F., the efficiency of the gelatin was increased enough so that the gelatin 

 content could be reduced one-fourth without impairing the quality of the ice 

 cream. Since no objectionable increase in bacteria occurs when the mix is held 

 at 68° F. for 6 hours, or in some cases for 10 hdurs, the ice cream manufacturer 

 can increase the efficiency of the gelatin in the mix by aging at 68° F. and yet 

 have at least 2 hours as a margin of safety from a detrimental increase in bacteria. 



SUMMARY 



1. The aging of pasteurized ice cream mixes for 6 hours at 68° F., whether 

 followed by aging for 18 hours at 38° F. or not, did not result in a significant 

 increase in the number of bacteria present. 



2. When a pasteurized ice cream mix was aged for 24 hours at 68° F., a definite 

 increase in the bacterial count did not occur until after the tenth hour. 



3. The aging of an unpasteurized mix for 6 hours at 68° F., whether followed 

 by aging for 18 hours at 38° F. or not, resulted in a material increase in the number 

 of bacteria present. 



4. The aging of a mix for 24 hours at 38° F. did not result in a material increase 

 in the number of bacteria present, which agrees with previous findings. 



LITERATURE CITED 



(1) Olson, N. E., and Fay, A. C. 1925. The bacterial content of ice cream. 



Jour. Dairy Sci. 8 (No. 5):415-444. 



(2) Mueller, W. S. 1933. Aging effects on gelatin dispersions. Indus, and 



Engin. Chem. 25 (No. 6):707. 



(3) Mueller, W. S., and Frandsen, J. H. 1933. Higher aging temperatures in 



the manufacture of ice cream. Mass. Agr. Expt. Sta. Bui. 302. 



(4) Standard methods of milk analysis. 6th edition, 1934. Published by the 



American Public Health Association. 



Publication of this Document Approved by Commission on Administration and Finance 

 5M-10-*H4. No. 2001. 



