SCIENTIFIC RESEARCH IN PRACTICE. 263 



fermentation yeast types were introduced into a brewery by the 

 author in the year 1884. It was urged, as an objection to 

 their adoption, that, in consequence of the high temperatures 

 at which such fermentations are conducted, the yeast would 

 not long remain pure. Experience has proved that this 

 objection is of no moment, and that in this section of the 

 brewing trade important progress may be made and consider- 

 able advantages realised by the use of a single selected type. 

 More recently, it has been stated that it is impossible to secure 

 a suitable after-fermentation with one species an objection 

 which had previously been erroneously urged in the case of 

 low-fermentation yeast. VAN LAER especially has laid stress 

 upon this supposed disadvantage ; and, while admitting that 

 there exist low- fermentation yeasts capable of carrying through 

 a normal after-fermentation, he has asserted that the writer 

 wrongly attributed the same properties to high-fermentation 

 yeasts. In spite of our accurate experiments, and although 

 practical results had been obtained with a single selected 

 species, even in English breweries, to which VAN LAER'S theory 

 (unsupported as it was by any exact evidence) especially 

 related, our experience was disregarded, and he prepared 

 mixtures of high-fermentation yeasts for use in breweries, which, 

 he claimed, are able to fulfil all practical requirements. Thus 

 the one species would carry out the principal, the other the 

 secondary fermentation. Indeed, the possibility of preparing 

 such a " composite yeast " cannot be denied ; but assuming 

 VAN LAER'S preparations yielded satisfactory results in the 

 breweries, it does not follow that these are due to the action 

 of the " composite yeast " as such. By no means ; it had first 

 to be proved that this new yeast was really a composite yeast 

 in practice, i.e. that the different species of which it was 

 composed were really able to co-operate. In conjunction with 

 J. CHR. HOLM, the author examined several of the preparations 

 sold for use in breweries, with the result that, even during the 

 first fermentation, one of the species prevailed at the expense of 

 the others, the latter entirely disappearing during the following 

 fermentations. Thus, it was shown that the problem of 

 preparing a real " composite yeast" had not been solved. The 

 experience gained in recent years, even in English breweries, 



