J 64 



Journal of Agricultural Research 



Vol. VT. No. 4 



A study of Table III shows that mold spores possess much greater 

 ability to withstand dry heat than heating in milk. Very few forms 

 were destroyed at i8o° F. (82.2° C), but they include Penicillium 

 hrevicaule, which has a thick-walled spore and in laboratory cultures 

 has remained viable at least 7 years. Only a few species of Penicillium 

 survived heating to 200° F. (93.3° C.) for 30 minutes. All these are 

 forms which grew at 98.6° F. (37° C), and some of them are widely 

 distributed. 



Aside from A. wentii, all the species of Aspergillus survived heating 

 at 200^ F. (93.3° C). Several of them survived at 230° F. (110° C), 

 but after 250° F. (121.1° C.) for 30 minutes no species showed growth 

 after 6 days' incubation. Three of six mucors, however, survived the 

 heating to 250° F. (121.1° C.) for 30 minutes. These species were killed 



quickly by both forms of heating 

 in milk. The results of these 

 experiinents are plotted in 

 figure 3. 



The destruction of mold spores 

 by dry heat has no relation to the 

 subject of pasteurization of milk, 

 but it is of scientific interest. 



DISCUSSION OF RESULTS 



These results with mold spores 

 agree in general with bacterio- 

 logical studies of pasteurization. 



Fig. 3.-Curve of the number of spedes of molds sur- Very few of thcSC Orgauisms 

 viving dry heat for 30 minutes at a series of temper- found in milk SUrvive af tCf 30 



minutes' heating to 145° F. (62.8° 

 C). Certain molds, notably Aspergillus fumigatus and A. flavus, do 

 survive, but they occur only occasionally in milk. Oidium lactis and the 

 mucors, which are probably more important as milk-borne organisms 

 than all the rest, are destroyed at the low temperatures used in the holder 

 process of pasteurization. In the flash process very few mold spores 

 survived at 165° F. (73.9° C). Occasionally some spores seem to have 

 escaped destruction at 175° F. (79.5° C), but the organisms surviving 

 in these cases were of minor importance in the decomposition of dairy 

 products. In confirmation of these results the writers have had access 

 to unpublished data of Mr. R. O. Webster, of the Bureau of Chemistry, 

 giving cultural analysis of butter made from flash-pasteurized cream on 

 a commercial basis. Cultures from this butter showed no mold spores, 

 while cultures made at the same time from country butter showed 20,000 

 to 60,000 per gram. 



