WHAT IS THE PURE YEAST OF PASTEUR? 137 



Internationale des Brasseurs de Paris en 1878" ('Revue Uni- 

 verselle de la Brasserie/ Paris, 1881, No. 372). They also 

 appeared in the report published by the Congress. In these 

 lectures he says : " If an acid be added to a saccharine 

 solution favourable to the growth of alcoholic ferments, the 

 development of disease ferments is thereby prevented. Acetic 

 bacteria can indeed live in an acid liquid, but they require a 

 high temperature for their development ; the other disease 

 ferments, on the other hand, cannot live in an acid liquid. 

 For the purification of brewery yeast, 4-5 per cent, of acid 

 (for instance, tartaric) may be employed. After four or five 

 cultivations in this liquid, one can be sure that the yeast is 

 pure ; the alcoholic ferments alone survive, being the most 

 vigorous and the most numerous." Pasteur, says Velten, 

 makes use of four such cultivations and each occupies 48 

 hours. It follows from the above that the sole object of this 

 purification of the yeast is the removal of the bacteria, and it 

 is stated that yeast thus purified consists of several species. 

 Duclaux also advocates the employment of this method for 

 purifying brewery yeast (' Chimie Biologique,' 1883, p. 301), 

 but he recommends only a small addition of tartaric acid. 



Shortly after the publication in 1876 of Pasteur's famous 

 ' Etudes sur la biere,' some experiments were made by the 

 late Captain J. C. Jacobsen at Old Carlsberg, and by Carl 

 Jacobsen at New Carlsberg, on the methods described in 

 that work for the purification of brewery yeast, and both 

 tartaric acid and carbolic acid were tried ; they gave no 

 satisfactory result, however, and were consequently com- 

 pletely relinquished. This was also the case in breweries 

 abroad in which similar trials were made ; and Pasteur's 

 methods did not even find favour in France. At the present 

 time Velten is the only brewer who recommends them, and 

 his own writings (' Wochenschrift fur Brauerei,' Berlin, 1886, 

 p. 5) show that he does not invariably employ them. 

 Velten's name is of high standing as the old associate of 



