390 MICRO-ORGANISMS AND FERMENTATION. 



The following notes may be given regarding their physio- 

 logical properties : 



The temperature limits for propagation are Torula (A). 

 40 to 40-5 C. and 5 to 7 C. ; Torula (B) 39-5 to 3-4 C. 

 Optimum temperature : 30 to 35 C. for both groups. They 

 have practically the same limits of temperature for existence. 

 It is worthy of note in this connection that the cells die in 

 fifteen to eighteen months in wort, but if a little calcium 

 carbonate is added life may be preserved for a long time,. 

 probably in consequence of the neutralisation of acid formed 

 by the cells. In bottled beer they can live for a long time. 



With respect to their reaction on sugars, it has been proved 

 that saccharose is easily fermented by (A), and less rapidly 

 by (B). Glucose and laevulose are easily fermented by both ; 

 maltose more readily by (-4) than by (B). Neither ferments 

 dextrin. Saccharose-yeast-water is fermented, but without 

 giving Fehling's reaction, for although inversion takes place, 

 the inverted sugar is immediately fermented. Lactose is 

 fermented only by Torula (B). It is easy to distinguish the 

 two groups through their physiological behaviour. 



They are not very sensitive to the alcohol and acid formed 

 during fermentation, so that at the end of the primary fer- 

 mentation they can hold their own in competition with Saccharo- 

 mycetes, and may, therefore, ferment the sugar residues with 

 which the Saccharomycetes are incapable of reacting. 



When Torula (A) is added to fully-fermented beer (Danish 

 export beer and Danish stout) or to wort, it forms acid along 

 with alcohol, which to some extent combines with the alcohol 

 and produces characteristic aromatic and flavouring ethereal 

 substances. The acid reaction of the liquid is also increased. 

 Torula (B), on the other hand, cannot develop further in these 

 beers, but by the addition of sugar a fresh fermentation sets 

 in, with peculiar aroma and flavour. This Torula is, there- 

 fore, unable to ferment the sugar residues if the beer has 

 already been well fermented. 



In addition to these two species, Schionning isolated from 

 English beers about 150 forms belonging to this group, possibly 

 only varieties or races of the typical species described. Most 

 of them are closely related to the Torula (A) group. Certain 





