200 



MINERAL FOODSTUFFS. 



facilitate the differentiation of natural and sophisticated wines by 

 the chemist, the latter wines usually containing phosphoric acid 

 solely in the form of (added) orthophosphates. 



260. The Importance of Sulphur. 



The value of sulphur in connection with the metabolism of 

 yeast is still in complete obscurity. The fact that this substance 

 is never absent in yeast samples justifies the inference that it is 

 indispensable for the growth of the plant. It is almost impossible 

 to prove this directly, i.e., by cultivation experiments, because up 

 to the present no one has succeeded in eliminating the sulphurous 

 impurities (vol. ii. p. 48) from the comparatively large amount 

 of sugar needed to furnish a sufficient crop of yeast for analytical 

 purposes, which impurities according to a calculation made by 

 Adolf Mayer suffice to supply the sulphur present in the proteid 

 substances of the crop. The next problem on the list, namely, 

 the nature of the assimilable sulphur compounds taken up by the 

 yeast, also remains unsolved. All that can be said at present is 

 that the sulphates (of calcium and magnesium), so greatly appre- 

 ciated by the higher plants, appear ill adapted for the construc- 

 tion of the yeast cell. The sulphur in these salts is eliminated 

 and expelled either as sulphur dioxide or even sulphuretted 

 hydrogen. Further information on this point will no doubt 

 be welcomed by fermentation technologists. 



The first reliable information on the production of sulphur 

 dioxide during alcoholic fermentation by yeast was supplied by 

 FR. PFEIFER (I.), who traced the gradual accumulation of this 

 reduction product in fermenting beer wort, and obtained the 

 following figures : 



SO 2 CONTENT IN MGRMS. PER LITRE. 



In saccharose solutions, treated with the necessary nutrient 

 salts (including ammonium sulphate), sterilised and inoculated 

 with a large quantity of yeast, 11.4 mgrms. of S0 2 were detected 

 at the end of five days, when fermentation was almost completed. 

 The same results were obtained by B. HAAS (I.) in his experi- 



