EXPERIMENT STATION BULLETINS. 



539 



TYPES AND NUMBERS OF MICROORGANISMS IN CREAM AND BUTTER AS IN- 

 FLUENCED BY THE MANIPULATIONS OF THE CREAM DURING 

 THE MANUFACTURE OF BUTTER. 



In this study we have for convenience grouped the microorganisms in 

 three groups : First, bacteria of the starter type ; second, gas-producers 

 (coli-aerogenes and anaerobic gas-producers) and the casein liquefiers; 

 and tliii'd, liacteria wliich are inert or inditferent in milk. 



F i 



2. Graphic representation, based on the log of "2", of the 



total number of microorganisms (auerage of ty>elve churnings) present at 

 different steps in the manufacture of butter. 



The total numJjer of hacteria found at different periods in the manu- 

 facture of butter is represented graphically in "Fig. 2." Pasteurization 

 kills a large percentage, the addition of starter adds enormous num- 

 bers, an increase is noticed during the period of ripening and at the time 

 of churning a marked decrease in the number of living bacteria is ob- 

 served. Neither the butter nor -the buttermilk from the churn contains 

 as many living bacteria as the ripened cream. In butter the total num- 

 ber of living bacteria decrease gradually. 



The starter group i.j by far the most numerous and plays an important 

 part in the ripening process. It is present in large numbers at everj' 



