2-3 THE YEAST CELL 



FROHBERG AND SAAZ TYPE BOTTOM FERMENTERS 



Bottom beer yeasts are again subdivided into vigorous and weak 

 fermenters. The vigorous fermenters are called Frohberg yeasts; 

 the weak fermenters are Saaz yeasts. There are many types of the 

 Frohberg yeasts, but only a few Saaz yeasts are known. Saaz yeasts 

 are generally low in vigor and therefore not desirable for most pur- 

 poses. Frohberg yeasts have long ellipsoidal cells and are obviously 

 diploid. Saaz cells are probable haploid and are much more variable 

 with occasional giant cells. Frohberg yeasts form few dauer cells; 

 Saaz cells are less viable than Frohberg. The optimum temperature 

 for both yeasts is 25° to 26 ; the maximum is 35 for Frohberg and 

 33° for Saaz. Saaz yeast is especially sensitive to alcohol. 



Many haplophase yeasts resemble the characteristic bottom fer- 

 menting yeasts in being autoagglutinable and weakly fermentative, 

 while most diplophase yeasts are top fermenters. 



BAKERS' YEASTS 



Distillery and bakers' yeasts are top fermenters. There are no 

 clear cut differences between top fermenting beer yeasts and distill- 

 ery and bakers' yeast, but they are not generally interchangeable. 

 A good bakers* yeast has the following characteristics: (1) keeping 

 quality, it does not autolyze nor lose viability excessively when held 

 in a cake for a few days at room temperature; (2) baking strength, 

 it causes dough to rise quickly; (3) high yield, it transforms the maxi- 

 mum amount of nutrients in the fermentors into yeast in the shortest 

 possible time. 



FOOD YEASTS 



Torulopsis utilis is widely used as a food yeast, but other stand- 

 ard variants of Saccharomyces have also been used for this purpose. 

 Torulopsis utilis was originally selected by Henneberg as a food 

 yeast when he observed that it was capable of crowding out bakers' 

 yeast in plants engaged in the production of baking yeast. Torulopsis 

 is not a fermenter and compressed bakers' yeast containing a large 

 proportion of this organism causes the dough to rise very slowly. 

 Complaints from bakers resulted in the original isolation of the Toru- 

 lopsis from the abnormally slow yeasts. Bakers' yeist is grown in 

 a heavily aerated nutrient medium. Generally speaking, Saccharo- 

 myces is adapted to relatively anaerobic conditions and heavy inocu- 

 lations are necessary in industrial practice to insure the predomi- 

 nance of Saccharomyces over chance inoculation by the more aerobic 

 Torulopsis. When the need for protein became acute in Germany 

 during the first World War, Henneberg proposed that pure cultures 

 of Torulopsis be used as a source. 



