5 io CHEMISTRY OF ALCOHOLIC FERMENTATION. 



The distilled spirits, cognac and brandy, also undergo changes 

 in storage, which changes are influenced by esterification, as well 

 as by other factors, such as storing the products in casks that are 

 (in contrast to those used for beer) neither lined with pitch nor 

 varnished. 



Besides these true by-products of alcoholic fermentation, we 

 have to consider substances that exist ready formed in the raw 

 materials, and are decomposed under the influence of fermentation. 

 These substances are principally glucosides which, on being 

 decomposed by enzymes, yield up their components to the 

 fermented liquid. This explains the occurrence of hydrocyanic 

 acid, benzoic acid, benzaldehyde, and benzaldehyde-cyanhydrin, 

 for instance, in cherry brandy according to K. WINDISCH (IV*) 

 and also of methyl alcohol in fermented fruit juices. In these 

 latter, prepared from plums, cherries, and apples, WOLFF (I.) 

 found, almost invariably, methyl alcohol in the proportion of i 

 per cent, of the ethyl alcohol present. In the case of wines prepared 

 from grapes with the stalks unremoved, the resulting alcohol 

 contained about 0.150.4 per cent, of methyl alcohol, whereas 

 wines from grapes freed from stalks furnished 0.03 per cent, at 

 most. The alcohol obtained by fermenting sugar with wine 

 yeast was, on the other hand, entirely free from methyl alcohol 

 in every case. 



The nitrogenous constituents of the yeast (see p. 2 1 8, vol. ii.) and 

 of the raw material undergo changes during fermentation. Thus 

 fermentation products have been found to contain the following 

 volatile and non-volatile compounds : ammonia, by KKUIS and 

 RAYMAN (II.) and by K. WINDISCH (IV.); trimethylamine, and 

 other amines, by ORDONNEAU (I.) and LUDWIG (I.) ; pyridin, 

 cullidin, &c., by KRAMER and PINNER (I.) and ORDONNEAU (1.) ; 

 6-glycosin, by MORIN (I.) and TANRET (V.) ; derivatives of pyrazin 

 and other bases, by SCIIROTTER (I.), OSER (I.), GUERIN (I.), STOHR 

 (I.), E. BAMBERGER and EINHORN (I.); leucin arid tyrosin. 



The distillates of fermented mashes and liquors also contain 

 other chemical compounds, which were formerly believed to 

 originate, at least in part, during alcoholic fermentation. Fore- 

 most among these is furfural, which was found by Kruis and 

 Ray man, more particularly associated with the formation of large 

 quantities of acetaldehyde. Furfural was discovered in 1882 by 

 K. FORSTER (L), in crude spirit, and also in the distillates from 

 wine and beer. He ascribed its formation to the effect of the 

 heat (boiling temperature) on the pentosans (see pp. 205 and 247, 

 vol. ii.) contained in the raw materials. Kruis and Rayman regard 

 furfural as a product of the metabolism of yeast, a view opposed 

 by CHAPMAN (I.). According to LINDET (VI.), it is formed only 

 during the fermentation of worts from raw materials (cereal 

 grains) that have been dissociated with acids, or when the fer- 

 mented mash has been distilled by direct fire heat. No furfural 



