500 CHEMISTRY OF ALCOHOLIC FERMENTATION. 



The aldehydes that are always formed during fermentation 

 should be regarded as intermediate products between the fatty 

 acids and the alcohols. Ordinary aldehyde (acetaldehyde) was 

 observed by BECHAMP (XIII.) and ROSER (II.). The cause of its 

 formation will be dealt with shortly. As was shown by DURIN (II.), 

 it can be easily recovered by strongly cooling the fermentation 

 gases in suitable vessels. In works where yeast is produced by 

 the aeration process, a considerable amount of aldehyde is formed 

 under the influence of atmospheric oxygen, especially in mashes of 

 maize, rice, and malt, the resulting spirit having an evil smell 

 and taste in consequence of its high content of aldehyde see 

 M.ERCKER (II.). JAKSCH (III.) also states that aldehyde is formed 

 during alcoholic fermentation. KAYSER (XIII.) regards aldehyde 

 as a product of the activity of the Saccharomycetes ; and, accord- 

 ing to KRUIS and RAYMAN (II.), considerable quantities of this 

 substance are formed when a film is produced and there is a 

 plentiful accession of air. Hence aldehyde is the result of the 

 oxidation of nascent alcohol. According to Ilges, it is not formed 

 during fermentation, but only in the distilling apparatus, by 

 contact of the spirit vapour with air compare M^ERGKER (IV.). 

 During the oxidation of alcohol, the formation of aldehyde is 

 accompanied by the production of acetal, the diethyl ether of 

 aldehyde, OH 3 .OH(OC 2 H 5 ) 8 ; and, according to GEUTHER (I.) and 

 WINDISCH (IV.), it occurs in fairly considerable quantities in 

 fermentation products, whilst ORDONNEAU (I.) found it in cognac. 

 Its formation can be easily explained, since, according to DURIN 

 (II.), alcohol and aldehyde come into contact in the nascent state 

 during the formation of the latter substance, so that the two may 

 unite to acetal, with elimination of one molecule of water. 



The influence of oxygen on alcholic fermentation by yeast will 

 now be considered, though its action on cell reproduction and 

 respiration has already been dealt with exhaustively on p. 231 

 Qt seq., vol. i. It may be mentioned at once that the favourable 

 influence of aeration on the fermentation of must, worts, and 

 mashes has long been recognised in practice, and was fully 

 established by a series of fermentation technologists between the 

 years 1867 and 1874. Blankenhorn did this in an imperfect 

 manner, then Moritz (partly in collaboration with Haas) ; also by 

 Molnar in the case of wine musts, and by ADOLF MAYER (VII.) 

 with nutrient solutions. More accurate researches were under- 

 taken, with wort by R. PEDERSEN (I.) in 1878. It was ascertained 

 that aeration increases both the working action on the extract and 

 also the (absolute) reproductive power of the yeast, though the 

 amount of extract consumed per unit weight of the yeast crop is 

 smaller in aerated worts than in others. The difference, however, 

 is not large as was proved arithmetically by D. IWANOWSKI (I.) 

 in 1893. In repeating Pedersen's experiment, E. C. Hariseii 

 (p. 233, vol. ii.) found that the amount of extract consumed per 



