THEORIES OF FERMENTATION. 245 



kinds of organisms. This was proved by E. C. Hansen in 1878 

 for acetic acid bacteria, by Miquel for uric acid bacteria, and 

 by Hansen in 1883 for the alcohol yeasts. 



The chief reason why the reform in brewing technique 

 could not be carried out was that the existing scientific stand- 

 point made it impossible to clearly define the relations existing 

 between the different fungi concerned in alcoholic fermenta- 

 tion. Pasteur was, therefore, unable to escape from the 

 indistinct assumptions and the contradictory views of his 

 predecessors. In a review given in his book (pp. 4-7) regarding 

 the micro-organisms that bring about diseases in beer, he 

 speaks only of bacteria, and this belief is reiterated by Duclaux 

 in 1883, and by other French, German, and English workers. 

 As a result of his studies, Pasteur recommended brewers to 

 undertake the purification of their yeasts, to rid them of 

 bacteria by cultivating them in a sugar solution with tartaric 

 acid or in wort with a little carbolic acid. 



In contrast to all this, in 1883 Hansen published his doctrine 

 that some of the most dangerous and most commonly occurring 

 diseases in low-fermentation beer are not produced by bacteria, 

 but by certain species of Saccharomycetes, and that the names 

 . cerevisice, S. Pastorianus, and S. ellipsoideus, suggested by 

 Beess, do not indicate one, but several different species and 

 races. Hansen proved that species which had been incorrectly 

 grouped under the systematic name S. cerevisice yield different 

 products in the brewery. From this standpoint he elaborated 

 Ms system, utilising a stock yeast derived from a single species. 

 After some opposition, this system was adopted in all brewing 

 countries, and introduced into the industry. Hansen's experi- 

 mental demonstration showed that Pasteur's process for 

 purifying yeast by means of tartaric acid furthers the develop- 

 ment of disease yeast to such an extent that they are capable 

 of completely suppressing the true culture yeasts. Pasteur 

 greeted Hansen's system as an advance, and wrote, " Hansen 

 was the first to realise that beer yeast should be pure, and that 

 not only in regard to microbes and disease ferments in the 

 narrower sense, but also that it should be free from cells of 

 wild yeast." 



The main problem regarding the actual cause of the decom- 



