506 CHEMISTRY OF ALCOHOLIC FERMENTATION. 



suppresses anaerobic bacteria. It should be borne in mind that 

 in nearly every case, except the so-called " Amylo process" (see 

 pp. 94 et seq.j vol. ii.), the grape, potato, and grain mashes 

 employed for fermentation are only imperfectly sterilised (addi- 

 tion of malt !), if at all, so that bacteria may gain access from the 

 start. 



In the case of brewing, where the worts are mostly sterilised, 

 few reports are met with, in the literature, concerning the forma- 

 tion of higher alcohols during fermentation. CHAPMAN (I.) distilled 

 six samples of English beers and found, per 100 parts of crude 

 alcohol, 0.051-0.250 part of fusel oil, as amyl alcohol, 0.021-0.062 

 part of esters, chiefly ethyl acetate, and traces of furfural. As 

 mentioned already on p. 504, vol. ii., ORDONXEAU (I.) ascribes the 

 formation of the higher alcohols to the vital activity of the yeast 

 itself. RAYMAN and KRUIS (I.) attempted to decide the question 

 by fermenting sterile worts with pure cultures of four different 

 yeasts and one of a species of Mycodenna. All the experiments 

 in which Sacch. cerevisice, L., furnished a low yield of fusel oil, 

 were performed with cells that had been cultivated for a long 

 time in the laboratory under unfavourable conditions. It seems 

 that the formation of amyl alcohol results from the yeast having 

 reached a certain state of exhaustion. According to M^ERCKER (V.), 

 on the other hand, it should be pointed out that grain mashes, 

 which are particularly well adapted for the energetic nutrition and 

 reproduction of yeast, greatly favour the production of fusel oil. 



A. high fermentation temperature is said by KRUIS and 

 RAYMAN (II.) to increase the yield of fusel oils. A yeast, other- 

 wise incapable of producing fusel oil in malt worts, furnished a 

 large quantity of amyl alcohol in an imperfectly sterilised yeast 

 mash that had turned sour spontaneously with formation of lactic 

 acid ; but no higher alcohols were formed by yeast and aeration 

 in a yeast that had been completely sterilised after turning sour. 

 It was also found that in all cases where fusel oil was produced, 

 the amount of acetaldehyde formed was merely small, and vice 

 versd. Hence, anaerobiotic conditions seem to contribute essentially 

 to the formation of the amyl alcohols. 



According to GENTIL (I.), the above experiments do not 

 sufficiently prove that fusel oils are produced by yeast, owing to 

 the conditions adopted, namely, the selection of a yeast previously 

 inhabiting a medium containing amyl alcohol, and the weakening 

 of the yeast by an abnormally high temperature and shortened 

 fermentation. Gentil himself failed to obtain amyl alcohol in 

 fermenting a solution of saccharose containing malt peptone as 

 yeast food. 



In subsequent experiments, KRUIS and RAYMAN (III.) found 

 that, contrary to the results previously obtained, the formation of 

 amyl alcohol is unaffected either by unfavourable composition 

 of the nutrient medium or by the age and physiological condition 



