214 BUTTER-MAKING. 



CREAM I. 



Sugar. Acid. ^ S^L 



1st ripening period 1% produced .04% .33% 



2d " '' 1 " .06 .35 



CREAM II. 



1st ripening period 1% produced .08% .58% 



2d " " 1 " .06 .64 



3d " " 1 " .045 .82 



CREAM III. 



1st ripening period 1% produced .051% -58% 



2d " " 1 " .050 .63 



3d " " 1 " .016 .68 



Average of Siexperiments 1 " .05 + 



Conn states that the lactic acid produced in cream during 

 ripening is not always of the same kind. Some species of 

 bacteria produce the kind which turns the plane of polarization 

 to the left; other species produce the kind which turn it to 

 the right, and still other species produce the so-called inactive 

 lactic acid. The most common are those which produce acid 

 that turns the plane of polarization to the right. 



The souring of cream, according to Conn, is not due to the 

 development of lactic acid alone. Two kinds are produced, 

 (1) fixed, and (2) volatile. The fixed acids appear to be chiefly, 

 if not wholly, lactic acid, and the volatile are chiefly acetic and 

 formic acids. The fixed acids are produced in the greatest 

 proportion. 



In the table quoted above, it will be seen that during the 

 first ripening period of sample 3, .1% sugar produced .051% of 

 acid, while during the last or third ripening stage .1% of sugar 

 produced .016% of acid, being only about one- third of that 

 produced during the first ripening period. The same is true 

 in experiment II, where three separate analyses were made of 

 the cream. It is difficult to account for the constant decrease 

 of lactic acid in proportion to the sugar decomposed in the 

 advanced stage of the ripening period. Is it the lactic acid 

 already present that decomposes into other products when so 

 much acid is formed? Or do the bacteria continue to decom- 

 pose the sugar, but the by-products being of a different nature? 





