HANSEN'S EXPERIMENTS WITH YEAST. 267 



stated that film cells may produce a disagreeable flavour. The 

 production of films, and therefore also their disturbing influence, 

 may be avoided by the preparation of an asporogenic variety, 

 which, as has already been shown, is incapable of film formation 

 (see p. 127, vol. ii.). 



The production of varieties with an increased or diminished 

 power of producing alcohol is also of importance in practice. 

 HANSEN (XLIII.) carried out experiments on this point, and, by 

 cultivating Carlsberg bottom yeast No. i in eight successive 

 cultures at 32 0. without aeration, obtained a variety which 

 gave 1-2 per cent, of alcohol (by volume) less in wort containing 

 10 per cent, of saccharose than the standard No. i yeast, whilst 

 at the same time it clarified the beer better. He also obtained 

 a variety with increased powers of alcohol production by growing 

 the same species, Carlsberg bottom yeast No. i, for several months 

 on wort gelatin with frequent renewal of the medium, whereas 

 13 per cent, (by volume) of alcohol was furnished by a vegetation 

 of the same original stock when grown in wort, under equal 

 conditions as regards time and renewal of the cultures ; finally, in a 

 wort containing 25 per cent, of saccharose, the variety obtained 

 by growing in wort gelatin produced 13.6 per cent, of alcohol 

 from the same final medium. By cultivating the spores of another 

 culture yeast, Sacch. cerevisice, on yeast- water gelatin, he also 

 obtained a variety furnishing more alcohol than the original stock 

 yeast, the increased production in this case being 3 per cent, by 

 volume, as compared with that given by the stock yeast grown in 

 wort throughout. According to Hansen the matter is one of 

 selection rather than modification ; but nothing more definite can 

 yet be expressed on the point. It may, however, be mentioned 

 that considerable differences in fermentative capacity are exhibited 

 by the individual cells of one and the same species in pure culture 

 in wort, even when grown under identical conditions; and this 

 applies also to their clarifying power. 



The variety obtained by Hansen from Carlsberg bottom yeast 

 No. i, by the method employed for producing asporogenic varieties, 

 was characterised by diminished attenuation and gave a beer of 

 greater palate fulness than the original stock ; but it exhibited 

 the defect of being too slow in action. 



There is evidently a wide field open for the practical application 

 of varieties of yeast obtained by treating the original stocks in 

 certain ways on the lines indicated above ; and important results 

 are undoubtedly obtainable by continuing these researches. We 

 will now deal briefly with the occurrence of variations in practice, 

 premising that lucid experimental investigations in this connection 

 are still lacking. As already stated, such variations have been 

 observed from the time pure-culture yeast was introduced into 

 practice, but there is little use going into details, since all that is 

 known is based on more or less uncertain observation. Reports 



