EXPERIMENT STATION BULLETINS. 479 



as c'omipajred with other OTgianisimis in the finiis'hed ice cream is strikingly 

 high." 



Hammer (2) investigated the number of bacteria at vairioms stages in 

 the mjanmfactnre of ice cream land condnded "that it is possible to pro- 

 dnoe ice cream in quantities, up to 20 galloins at least, with a low bacter- 

 ial coTint without expensive methods, though it is not certain that this is 

 true under large facton'y conditions." Hammer amd Goss (3) studied the 

 influence of freezing, hardening, and storage on the bacterial conteint of 

 ice cream' and concluded that, "there i's no e\4dence that tlhere is an in- 

 crease in tihe numlbers of contained organisms during the proper storage 

 of ice cream wlhile icommOnly there is a dieorease." Their results wei'e 

 based on colonies developing on agar held at 37° C for 48 hours. They 

 also say that, "there is an apparent increase in the number of bacteria as 

 determined by the plate method during the fireezing of ice cream." Oon^ 

 oeming the proce.^ of hardening they found tihiat, "there is usually a 

 decrease in the number of bacteria in ice cream during the hardening 

 process, presumiably >as la couisequence of the destructivie action of the 

 lowered temiperatuires." 



In a continuaition of the istudy of bacteria in ice cream Hammer 

 and Sanders (4) studied the influence of piasteurization lamd homogeniz- 

 ing upon the bacterial content of the ice cream max and repoi't as fol- 

 lows : "The pasteuirizatiom of the mix reduced the bacterial content very 

 satisfactorily. The method of pasteurizing and homogenizing the mix 

 should be considered as satisfactory for the production of ice cream with 

 a low baicterial count." 



Peterslon and Tracy (15) made bacterial counts on two batches after 

 the completion of each step in the manufacturing process to determine the 

 relative importance of each fstep. Their results indicate "that after 

 the mix is drawn from the pan the subsequent steps in the operatiou will 

 result in the addition of only a very small number of bacteria if ordinary 

 precautions are taken against recontamination. The increase after homo- 

 genizing and freezing is probably due, for the most part, to the breaking 

 up of the bacterial clusters, which results in a higher count by IJhe plafte 

 method." 



The influence of storage upiou the bacterial content of ice cream has 

 been studied hj several workers. Stiles and Penningtoin (5), Gordon 

 (6), Haimmier (2), Esten and Mason (7) amd EUienberger (8) and otihers 

 have worked upon tbis phase of the problem land covered iit quite com- 

 pletely. 



PRESENT WORK 



The present work is a study of the influence of the various manufac- 

 turing operations upon the ^number of bacteria in vanilla ice cream made 

 under factory conditions. The samples of the various batcihes were taken 

 at irandom from the first of September to the first of July. The workers 

 in .the factory were not aware that any attempt was being made to cbeck 

 the sanitairy qualitry' of their work. As a miatter of fact siamples of ice 

 cream were itaken daily at this plamt foir fat determinations and bacterial 

 counts, so that their suspicions mever were airoused so as tO' induce them 

 to take any unusual sanitary precautions to produce ice cream of low 



