PRODUCTS OF ALCOHOLIC FERMENTATION. 2G7 



The Products of Alcoholic Fermentation. 



It has already been stated that saccharose can only be 

 fermented after the intervention of invertase has caused 

 absorption of water and decomposition into glucose and 

 Isevulose. The same holds good with regard to maltose, which 

 is split up into two molecules of glucose. In a similar way 

 lactose is split up by certain species of yeast before alcoholic 

 fermentation takes place. Other sugars (the hexoses) are 

 directly fermentable. Of these, the commonest is glucose or 

 dextrose (grape sugar), which is fermented by every known 

 species of alcoholic yeast. This also applies to Isevulose or 

 fructose, which is so widely distributed in the vegetable 

 kingdom, and usually occurs in conjunction with dextrose. 

 Invert sugar is a mixture of the two. 



The principal product of fermentation is alcohol, more 

 particularly ethyl alcohol. In 1815 Gay-Lussac first estab- 

 lished the true character of the reaction when he showed that 

 cane sugar (more correctly grape sugar) gave 51-11 per cent, of 

 alcohol and 48-89 per cent, of carbon dioxide on fermentation. 

 Pasteur showed that by-products always occur, and that part 

 of the sugar is utilised for the nutrition of the yeast, so that 

 it is never possible to convert the whole amount of sugar 

 into alcohol and carbon dioxide. Pasteur's results were 48-3 

 per cent, of alcohol and 46-4 per cent, of carbon dioxide, which 

 agrees well with recent determinations, showing that practically 

 equal quantities of alcohol and carbon dioxide are formed. 

 It has already been stated that in all probability lactic acid 

 is formed as an intermediate product in the fermentation, as 

 shown by Buchner and Meisenheimer's work on the action 

 of yeast juice. 



Rayman and Kruis proved that beer which had been 

 subjected to fermentation with absolutely pure cultures, and 

 kept for some years at the usual temperature, contained only 

 ethyl alcohol, but when air was introduced and the yeast 

 formed a film, the alcohol was decomposed into carbon dioxide 

 and water. 



Glycerine occurs in varying quantities, and, according to 

 Wortmann and Laborde, this does not depend entirely on the 



