FERMENTATION 467 



carbonic acid gas to the cells, and it has not yet been possible to 

 convert the one form into the other. 



Characters of some of the more important yeasts. Hansen divides 

 the important yeasts into groups having the same general characters, 

 and distinguishes the varieties in each by Roman numerals (I, 

 II, etc.). 



CEREVTSLS: GROUP. These are the yeasts producing the normal 

 fermentations resulting in beer, etc. They are round or slightly 

 ovoid cells, and four ascospores are produced. In old cultures long 

 sausage-shaped or even filamentous cells may be met with. 



8. cerevisice I. and II. These are bottom fermentation forms in 

 use at the Old Carlsberg Brewery ; the cells of No. II are rounder 

 and slightly larger than those of No. I, and ascospore formation is 

 more abundant. 



There is also a top fermentation form described by Hansen 

 (S. cerevisice I top), which is the yeast employed in the breweries of 

 London and Edinburgh. 



The yeasts of the cerevisice group can invert cane sugar, select 

 dextrose from Isevulose, and ferment maltose, but they cannot 

 ferment lactose, nor decompose malto-dextrin. 



PASTORIANUS GROUP. These are wild yeasts. The cells are 

 elongated or sausage-shaped, and six or eight ascospores are pro- 

 duced in a cell. 



8. pastorianus I. A bottom fermentation yeast producing a 

 bitter taste in beer. 



8. pastorianus II. A feeble top fermentation form. Surface 

 cultures on yeast-water gelatin have smooth edges, which dis- 

 tinguishes it from the next species. 



8. pastorianus III. A top fermentation form producing turbidity 

 in beer. Surface cultures on yeast-water gelatin have woolly margins. 



ELLIPSOIDEUS GROUP. These are wild yeasts. The cells are 

 usually ovoid, or pear-shaped, sometimes round, rarely elongated. 



Five or six ascospores are produced in a cell. 



8. ellipsoideus I. A bottom fermentation yeast occurring on 

 ripe grapes. 



S. ellipsoideus II. A bottom fermentation yeast causing turbidity 

 in beer. 



Both the pastorianus and ellipsoideus groups resemble the cerevisice 

 group in their chemical actions, but they are able in addition to 

 decompose malto-dextrin. 



8. anomalus is a yeast forming small ovoid cells. It is curious 

 in that the spores are hemispheres with a projecting rim at the base 

 like a bowler hat. 



