ALCOHOLS AND ESTERS. 507 



of the yeast. The alcohol is formed only when certain carbo- 

 hydrates are present ; and the assumption is put forward that 

 amyl alcohol is formed, not from the hexoses ( 326), but from 

 other sugars that result from the polymerisation of the poly- 

 saccharicles always present in the cereals employed as the raw 

 material. In ten experiments with glucose, fructose, saccharose, 

 and beet juice, ethyl alcohol alone was produced, though, on the 

 other hand, amyl alcohol in considerable quantity resulted from 

 the use of barley worts and inverted brewers' grains, which sub- 

 stances contain fat (see below on this page). 



EMMERLING (XL), on the other hand, believes, from his tenta- 

 tive experiments, that fusel oils are not produced in more than 

 minimum quantities, if at all, in fermentations from which bacteria 

 have been rigorously excluded. He concludes that the amyl alcohols 

 originate in carbohydrates, and are produced by bacteria that are 

 of widespread occurrence and are almost invariably found on the 

 skin of potatoes. 



Great influence on the formation of fusel oils is exerted by the 

 nature of the substance to be fermented, the presence of fat being 

 a contributory factor according to BORNTRAGER (II.). Fermenta- 

 tions with materials that have been freed from fat yield very little 

 fusel oil. 



Sugar and carbohydrates are usually regarded as the sources 

 of the higher alcohols ; but, according to BAU (XXII.), there is 

 another possibility that should not be left out of consideration, 

 namely, the formation of these substances from the fat that is 

 ready formed in the mash and is generated from sugar by yeast, 

 to be stored up and afterwards decomposed again. During fer- 

 mentation the process of hydration is accompanied by those of 

 oxidation and reduction. Moreover, in industrial mashes, one 

 has to reckon with the presence of bacteria, a number of which 

 are endowed with powerful reducing properties. According to 

 DURIN (III.), aldehydes are formed, not only by the oxidation 

 of alcohol, but also by reducing actions occurring during fermen- 

 tation, the nascent aldehyde being then capable of easy reduction 

 to alcohol. 



Lactic acid (see p. 481, vol. ii.) may be regarded as the originat- 

 ing material for the formation of propyl alcohol, this alcohol being 

 found, according to BOUCHARDAT (1.), among the products of lactic 

 fermentation. Frrz (XIV.) states that it is also formed during 

 the fermentation of glycerine by fission fungi. 



According to BAU (XXII.), the higher alcohols originate from 

 the fatty acids derived from fats ; and indeed, butyric acid, 

 caproic acid, caprylic acid, and capric acid are frequently met with 

 in fats. When these acids are liberated by lipase (see p. 494, vol. ii.), 

 they may, in the nascent state, be reduced to alcohols, especially in 

 symbiotic fermentations by yeast and bacteria ; indeed, numerous 

 organisms are known that even eliminate free hydrogen. 



