488 ENZYMES 



catalase, carboxylase, peroxidase, etc. Of the common 

 hexoses only three, namely, glucose, fructose, or mannose, are 

 readily susceptible to direct attack by this yeast, while 

 galactose is only slowly acted upon ; ordinary yeast may, 

 however, be trained to acquire the power of fermenting 

 galactose more readily by cultivating it for some time in a 

 solution containing galactose ; some strains such as Saccharo- 

 myces apiculahis, S. Liidwigii, and 5. anomalus are, however, 

 without action on galactose. 



The ability of S. cerevisecs to ferment disaccharide sucrose 

 and maltose was formerly thought to be due to their possessing 

 the enzymes saccharase (or invertase) and maltase, which 

 were supposed to effect a preliminary hydrolysis of the cor- 

 responding disaccharides ; Willstatter * has, however, found 

 distillery yeasts, containing very little maltase, which were 

 able to ferment maltase quite readily, and, to a lesser 

 extent, lactose though entirely deficient in lactase ; it is even 

 suggested by Willstatter that sucrose may be susceptible of 

 direct attack without the intervention of saccharase. 



From what has gone before it will be noted that practically 

 all yeasts contain maltase, but as a general rule brewers' 

 yeasts are richer than distillers. Yeasts are without action on 

 pentoses. Technically a distinction is made between brewery 

 and distillery yeast ; the strains employed by distillers are 

 selected for their so-called high attenuating power, which means 

 their abihty to effect the alcohoHc fermentation of practically 

 all the saccharified carbohydrate in the substrate, and thus 

 produce a maximum yield of alcohol ; yeasts of this type 

 go by the name of " Frohberg," from the name of the distillery 

 from which the most marked representative of the class was 

 first produced. Brewers, on the other hand, desire to leave in 

 the fermented liquor an appreciable quantity of unfermented 

 carbohydrate both sugar and dextrin, and for this purpose 

 make use of a yeast which yields a higher gravity liquid after 

 fermentation ; this type of yeast is known as the " Saaz " type. 



In addition to the above two types of yeast, brewers further 

 distinguish between top and bottom fermentation yeasts ; 

 * Willstatter : " Zeit. physiol. Chem.," 1925, 150, 287. 



