ALCOHOLIC FERMENTS. 175 



some of which are sharply defined, whilst in others the out- 

 line is indistinct. The temperature limits for spore-formation 

 are 32 and 0*5 C., the optimum temperature being 24 C. 

 The temperature limit for the vitality of the vegetative cells 

 in wort is 70 C. In old films very numerously-branched 

 clusters occur. Besides causing yeast-turbidity, this species 

 also imparts a sweetish, disagreeable, aromatic taste to beer, 

 and a bitter, astringent after-taste. The yeast sediment 

 always has a dark colour. 



SACCHAROMYCES ILICIS. GRONLUND 



which was found on the fruit of Ilex Aquifolium, is a bottom- 

 fermentation yeast, consisting mainly of spherical cells. The 

 temperature limits for spore-formation are 8 and 38 C. The 

 spores have no vacuoles. In the films, slightly-elongated cells 

 are found. Streak cultures on gelatine have a floury, but 

 otherwise a variable, appearance. This species, grown in wort, 

 imparts a disagreeable, bitter taste. According to Schjerning 

 it contains invertase, and induces alcoholic fermentation in 

 solutions of saccharose, dextrose, and maltose. In ordinary 

 beer wort it can produce about 2*8 per cent, alcohol (by 

 volume). 



SACCHAROMYCES AQUIFOLII. GRONLUND 

 was also found on the fruit of Ilex Aquifolium. It is a top- 

 fermentation yeast, and consists of large round cells. The 

 temperature limits for spore-formation are 8 and 31 C. ; 

 the spores contain vacuoles. In the films, spherical and egg- 

 shaped cells alone occur. Streak cultures in gelatine vary in 

 appearance, some being glossy and some floury. This species 

 imparts to wort a disagreeable, sweet taste, with a bitter after- 

 taste. It inverts saccharose and induces alcoholic fermentation 

 in solutions of saccharose, dextrose, and maltose. In ordinary 

 beer-wort it can produce about 3*7 per cent, alcohol (by 

 volume). 



SACCHAROMYCES PYRIFORMIS. MARSHALL WARD 

 (see ginger-beer plant, page 71). 



