THE NON-VOLATILE BY-PRODUCTS. 491 



glycerine when digested with water at 4o-4iC., 30 grs. of yeast 

 yielding 0.19-0.335 grm., or 2.5-2.87 per cent, when referred to 

 the weight of the sugar. The production of glycerine is increased 

 when the fermentation is accelerated by working under reduced 

 pressure, with an augmented quantity of yeast and at a higher 

 temperature. Both MORITZ (II.) and also THYLMANN and HILGER 

 (I.) found the production of glycerine diminished by retarded 

 fermentation and lower temperature, as well as at temperatures 

 exceeding 35 C. accompanied by the first-named condition, 

 whereas, on the other hand, it is increased on the yeast being 

 provided with added nutriment, on accelerated fermentation, and 

 by using more highly concentrated solutions of sugar. In Moritz's 

 experiments the ratio between the alcohol and glycerine produced 

 ranged from 100 : 9.3 to 100: 13.8, and in those of Thylmann and 

 Hilger, 100 : 1.638 to 100 : 11.78, i.e., between very wide limits. 



MORITZ (II.) reports that, according to Miiller-Thurgau, the 

 amount of glycerine produced is determined by the greater or 

 smaller vital energy of the yeast, and is in direct relation there- 

 with, the fluctuations in the alcohol -glycerine ratio being thus 

 explained. The absence of a definite relation between the sugar 

 consumed and the glycerine produced was also mentioned by 

 STRAUB (I.), whose results agreed in other respects with those 

 of KULISCH (IV.) and of Thylmann and Hilger. The amount of 

 glycerine does not increase proportionally with the alcohol content ; 

 it is increased by supplying the yeast with an abundance of food, 

 especially such as contain nitrogenous substances. 



After Miiller-Thurgau, in 1884, had expressed the opinion 

 that glycerine is a metabolic product of yeast and not one of fer- 

 mentation, the following result was obtained by WORTMANN (XX.) 

 from the examination of 41 samples of must, fermented with pure 

 yeast : namely, that the normal ratio of alcohol to glycerine varies 

 between 100 : 7 and 100 : 14. Pure yeasts furnis ha lower average 

 yield of glycerine. The alcohol-glycerine ratio is not a criterion of 

 the quality of the wine. The quantity of glycerine produced is 

 not proportionate to the number of active yeast cells present, but 

 is largely dependent on the specific glycerine-forming capacity of 

 the race of yeast, as well as on the composition of the must. The 

 production of glycerine is not -influenced by the ash content of the 

 must, or the quantity of yeast ; and there is no mutual relation 

 at all between the various fermentation and metabolic products. 

 At a later date, WORTMANN (VII.) expressed himself still more 

 strongly on this point. The amount of any nutrient substance 

 present in must or taken up by the yeast forms no measure of the 

 quantity of any metabolic product obtained. The formation of 

 alcohol and carbon dioxide proceeds quite independently of the 

 formation of glycerine. 



LABORDE (VII.) also regards the amount of glycerine produced 

 as a characteristic racial feature of the various yeasts, having 



