494 CHEMISTRY OF ALCOHOLIC FERMENTATION. 



the beer or other fermented liquid. It is probable that Buchner's 

 expressed yeast juice contains lipase and fat (from the yeast). 

 This supposition has much to recommend it, since, despite 

 numerous researches, no regular connection has been discovered 

 to exist between the amount of sugar fermented and of glycerine 

 formed. 



Isobutylene glycol was found by HENNINGER (I.) in a red 

 Bordeaux wine, the amount being estimated at 0.05 percent., or 

 one-fiftieth of the quantity of glycerine present. It is doubtful, 

 however, whether this substance is a fermentation product ; and it 

 most probably existed in the must already, or was formed during 

 the process of recovery. According to BUTLEROW (I.), isobutylene 

 is formed in the decomposition of amyl alcohol by heat. SANSON 

 (I.) frequently detected isobutylene glycol, and according to WIN- 

 DISCH (V. ) it occurs also in cherry brandy. 



Experiments in connection with glycerine have frequently been 

 combined with the determination of succinic acid. BEISSENHIRTZ 

 (I.) is usually credited with the discovery of this substance in 

 alcoholic fermentation, though he only found it in a case of acetous 

 fermentation of a mixture of bread, carob beans, honey, vinegar, 

 brandy, and water. In 1853, SCHUNCK (II.), in the course of an 

 alcoholic fermentation set up, as he believed, by the enzyme of 

 madder erythrozyme (see p. 459, vol. ii.) observed the forma- 

 tion of carbon dioxide, a little hydrogen, and considerable quantities 

 of alcohol, accompanied by a small amount of succinic acid. How- 

 ever, the proof that this acid is a constant by-product of alcoholic 

 fermentation was due to C. SCHMIDT (II.) and PASTEUR (XXXI.), 

 the latter, as already mentioned, obtaining 0.673-0.76 per cent, 

 of this acid from sugar, and explaining its formation by the 

 equation given on p. 490, vol. ii. 



Broadly speaking, the hypotheses on the formation of succinic 

 acid are the same as in respect of glycerine. According to BOUSSIN- 

 GAULT (II.), the yield of succinic acid increases with the tempera- 

 ture, quantity of yeast, and reduction of atmospheric pressure ; 

 NORIN and CLOUDON (I.), on the other hand, stating that it 

 decreases when air is excluded, and increases when the fermen- 

 tation is conducted with access of air. The amount produced 

 during the various stages of fermentation varies. KAYSER and 

 DIENERT (I.) found that the quantity increases at first, diminishing 

 toward the close of fermentation, whilst EFFRONT (XII.), on the 

 contrary, observed a continuous increase in the amount of this 

 acid, the maximum being reached in the final stages of the 

 process, e.g. : 



after 24 48 72 and 96 hours 



0.025 0.045 0.068 and 0.092 per cent. 



THYLMANN and HILGER (I.), inter alia, ascribe the increase or 

 decrease of succinic acid to the same causes that operate in the 

 case of glycerine. 



