29 



valuable for a baker than the one in number 3 tube, because it produces 

 more eas : but this variety would not be suitable for other purposes, — 

 say for the manulacture ot wme. 



In the same wav, a yeast used for the making- of champag^ne would 

 not be suitable for making- beer ; and such is the influence of the yeast on 

 the flavour of the product, that very g-ood imitations of certain wines 

 may be made by g-rowing in apple juice the yeast taken from the wine. 



Fig. 38, Feniientation tubes containing flour and water— 



1. With addition of a distillery yeast. 



2. " " brewery yeast. 



■5. " " dried cake yeast. 



Note, in the right anns of the tubes, that there is more gas in 1 than 

 in the others, i-howing the more energetic working of the distillery 

 yeast. For the same reason, there is more gas in 2 than in 3. 



The injurious yeasts are also quite numerous. Besides those we 

 have already spoken of, we might mention those that produce bitterness, 

 not only In wine, but occasionally in milk and cheese. These yeasts 

 grow in milk, feeding upon the milk sugar, changing it into other com- 

 pounds, and giving rise to an unpleasant bitter taste, which aff"ects, not 

 only the milk, but the cheese made from it. 



