248 THE BOOK OF CHEESE 



decreased, while butyric and caproic acids continually in- 

 creased during the experimental period covered. Formic 

 acid was detected in the whole-milk cheese only at the 

 five and one-half month stage. In the judgment of 

 the experimenter the principal source of acetic and 

 propionic acids was probably lactates. Traces of these 

 acids may have had their origin in protein decomposition 

 or further fermentation of glycerine. The principal 

 sources indicated for butyric and caproic acids were fats 

 and proteins. 



The distillate from the experimental cheese was desig- 

 nated " flavor solution " and contained alcohols and 

 esters, giving a close resemblance to the cheese aroma. 

 The " flavor solution " from the mild whole-milk cheese 

 contained esters made up largely of ethyl alcohol and acetic 

 acid, while from the more pungent skimmed-milk cheese 

 the esters were largely compounds of ethyl alcohol and 

 caproic and butyric acids. The alcohol may have come 

 from the lactose fermentation. It appears to be an im- 

 portant factor in flavor production. The agencies opera- 

 tive in the production of volatile acids and syntheses of 

 esters are as yet undefined. 



232. Milk-sugar. The milk-sugar (lactose) is changed 

 into lactic acid by the lactic acid-forming organisms, 

 within the first few days after the cheese is made. 

 This acid is combined with the other constituents as fast 

 as it is formed. After a few days, the milk-sugar will 

 have entirely disappeared from the cheese. 1 The relation 

 between the milk-sugar and lactic acid is very close. It 

 is necessary that milk-sugar be present in order later to 

 have the lactic acid develop. 



1 Babcock, S. M., et al., Cheese ripening as influenced by sugar, 

 Wis. Exp. Sta. Kept. 1901, pages 162-167. 



