492 CHEMISTRY OF ALCOHOLIC FERMENTATION. 



obtained 2.5-7.75 per cent, of glycerine (mean 3 per cent.) per 

 100 grms. of sugar, from one and the same wine must. The pro- 

 duction of glycerine is in inverse ratio to the activity of the yeast, 

 and increases more particularly when nitrogenous foodstuffs to 

 which the yeast has not been habituated such as Liebig's meat 

 extract, yeast water, &c. are added to the must. An increase is 

 also observed at higher fermentation temperatures, with stronger 

 sugar solutions, and when the medium is strongly acidified with 

 tartaric acid. On the other hand, a diminution is observed when 

 artificial nutrient solutions are used, as well as in sugar solutions 

 to which alcohol has been added previous to fermentation. To 

 some extent the production of glycerine by a given yeast will vary 

 according to the kind of sugar present, 3.15 grms., for instance, 

 being obtained from galactose and inverted milk sugar, as com- 

 pared with 2.45 grms. from glucose, fructose, saccharose, and maltose 

 under identical conditions. A lactose yeast produced 1.75 grms. 

 of glycerine per 100 grms. of sugar in a solution of lactose, but 

 3.16 grms. in the case of inverted lactose. 



At the commencement of fermentation the formation of 

 glycerine is smaller than toward the end, EFFRONT (XI.), for 

 instance, obtaining at the end of 



24 48 72 and 94 hours 



- I 5 -35 4 and 0.91 per cent, of glycerine. 



According to this same worker (XII.), yeast that has been 

 habituated to preservatives (see vol. i, p. 251) will also produce 

 glycerine, the capacity, however, diminishing progressively as the 

 habituation proceeds, so that, eventually, it is possible to obtain 

 fermentations that run their course in accordance with the 

 theoretical equation, no by-products being formed. 



A very large number of experiments have been devoted to 

 determining the ratio between alcohol and glycerine in wine ; and 

 a few of the figures may be reproduced here. For example, 

 according to BORNTRAGER (XIII.), the ratio in question is 100: 

 6.0; RETKOW (I.) gives it as 100:5.6-12.8 in white wine and 

 100:7.0-11.83 in red wine; and WINDISCH (II.) 100:6.1-10.2. 

 The fluctuation of the values obtained by accurate experiment 

 with reliable wines makes it impossible to place any legal 

 restrictions on the amount of glycerine, and such a measure 

 would only open the door to chicanery. 



As regards the formation of glycerine in beer, BORGMANN (I.) 

 fermented samples of one and the same wort with two different 

 pure cultures of yeast, and found the beers to contain 0.109 an d 

 0.137 per cent., respectively, of glycerine, the ratio of alcohol to 

 glycerine being therefore 100:2.63 and 100:3.24. In beers 

 prepared without pure-culture yeasts, the ratio was 100:4.14 to 

 100:5.497. AMTHOR (IV.) also fermented beer worts with 

 pure cultures of eight different races of yeast, and found the 



