THE NON-VOLATILE BY-PRODUCTS. 493 



percentage of glycerine remarkably low, being only 0.1113 P er 

 cent., as compared with an average of 0.144 ^ n beer from Elsass, 

 and 0.1266 per cent, in Bavarian beer. The minimum ratio of 

 alcohol to glycerine was 100 : 1.65, the maximum being 100 : 4.3, 

 and the mean 10 : 2.38. 



Following the example of PASTEUR (XXXI.), most wt rkers 

 regarded sugar as the source of glycerine during fermentation. 

 UDRANSKY (I.), however, who took yeast that was free from sugar 

 and contained originally 0.053 per cent, of glycerine, and digested 

 it with alcohol, found that, without any autodigestion having 

 occurred in the yeast, the glycerine content increased by 116-285 

 per cent, of the original quantity and even by 355.2 per cent, 

 at the end of 13 months though no sugar had been added. 

 Lecithin is probably the antecedent from which the glycerine is 

 formed, since, under certain conditions, that substance which 

 was also found in yeast by HOPPE-SEYLER (VII.) (see p. 174, 

 vol. ii.) decomposes into fatty acids, cholin and glycerophosphoric 

 acid, the latter being readily split up into phosphoric acid and 

 glycerine. DUCLAUX (XXVI.) believes in the existence of special 

 enzymes that furnish glycerine and succinic acid, pure zymase 

 (alcoholase) probably decomposing sugar completely into carbon 

 dioxide and alcohol. BUCHNER and RAPP (XI.) nevertheless 

 consider that, from the chemical point of view, this decomposition 

 of sugar is a far more complex process than the inversion of sugar, 

 for instance, so that the constant appearance of by-products is 

 not surprising, these being found in all complicated reactions. 

 The problem has been solved by means of an experiment in cell- 

 less fermentation, in which BUCHNER and RAPP (X.) found that 

 100 grms. of saccharose furnished 0.5 grin, of glycerine and 0.3 

 grm. of succinic acid, that is to say, smaller proportions than 

 PASTEUR (XXXI.) and others obtained in fermentations with 

 yeast. After LAXA (II.) had discovered a fat- decomposing 

 enzyme, lipase, in yeast (see p. 66, vol. ii.), DELBRITCK (XI. and 

 XII.) expressed the opinion that glycerine is produced by the 

 decomposition of fat (the glycerine ester of a fatty acid) by lipase. 

 A similar hypothesis had previously been advanced by ROMMIER 

 (II.). Distillery washes always contain fat, from the raw grain 

 used, but in the preparation of wort, most of the fat is left 

 behind, though it may be assumed that a little fat and especially 

 lecithin is present in the wort, in an emulsified condition if 

 not in solution. On the other hand, the glycerine content of 

 beer (and also wine) is so high that it can hardly be derived from 

 the fat present in the wort. Yeast, however, according to NAGELI 

 and LOEW (III.), always contains fat (see p. 173, vol. ii.), small 

 globules of which can be often detected in the cells under the 

 microscope (see p. 155, vol. ii.). Fat is therefore occasionally 

 stored up by the yeast cells, and at other times decomposed again 

 by lipase, the fission products (glycerine) finding their way into 



