242 CHEMICAL INFLUENCES ON YEAST. 



H. MULLER-THURGAU (XIV.) has shown that yeast cells in a 

 nutrient medium in which the alcohol produced by their own 

 activity gradually reaches menacing proportions, assume the con- 

 dition of resting cells (seep. 118, vol. ii.) which remain at the 

 bottom of the liquid, and are incapable of setting up fermentation 

 when transferred to a fresh, non-alcoholic nutrient solution. 

 Under these latter conditions, however, they produce in a short 

 time daughter cells, which effect the fermentation of the proffered 

 sugar. The prevention of this formation of resting cells is the 

 main cause of the beneficial effect resulting from the practice of 

 stirring up the yeast with a stick, &c., when fermentation grows 

 sluggish in the must. When fermentation has reached the stage 

 at which the wine begins to clarify by the deposition of the yeast, 

 the consumption of sugar and formation of alcohol are effected 

 almost entirely by the sedimental yeast collected at the bottom of 

 the vessel. This alcohol, however, diffuses with considerable diffi- 

 culty in the already strongly alcoholic liquid, its buoyancy being 

 insufficient to overcome the frictional resistance. Hence a stratum, 

 rich in alcohol, is formed immediately above the sedimental yeast, 

 the upper cells of which are converted, under its influence, into 

 the resting condition, and constitute a wall separating the active 

 yeast from the still saccharine liquid, so that fermentation is 

 arrested. The object of the stirring is to alter this state of 

 things and remix the yeast with the liquid. The researches of 

 J. WORTMANN (VII.) on the yeast content of bottled wines con- 

 firm the above recorded observation of Mliller-Thurgau, the 

 presence of budding fungi (yeasts and torulse), capable of repro- 

 duction, having been detected in twenty-eight out of fifty-four 

 samples of wine of guaranteed age in bottle. 



The discovery and use of yeasts possessing high powers of 

 resistance and low sensitiveness toward alcohol has proved espe- 

 cially useful to makers of wine and fruit wine ; in the first place 

 for artificially incited secondary fermentation, then for re-fermen- 

 tation, and, finally, for the production of champagne (see p. 188, 

 vol. ii.). Similar interest attaches to the preparation of Sake, 

 the Japanese rice wine, which, according to A. SCHUOHE (II.), 

 usually contains 14 per cent, (by weight) of alcohol, and occasionally 

 even 18 per cent. 



The foregoing particulars relate exclusively to ethyl alcohol. 

 With regard to the influence exerted on the fermentation activity 

 of yeast by the homologous allies of this alcohol, certain experi- 

 ments were instituted, first by P. REGNARD (I.) with an un- 

 specified yeast in 1889, and then in 1897 by K. YABE (III.) with 

 the Sake yeast mentioned on p. 240. The former used for each 

 10 grms. of yeast, 250 c.c. of an 8 per cent, solution of grape 

 sugar, i.e., a not particularly favourable nutrient medium. No 

 fermentation ensued in the cultures when treated with the 

 following additions (per cent, by volume) : 



