STUDIES ON FERMEISTATION. 231 



In the place of flasks we may make use simply of shallow 

 basins, covered with sheets of glass, such as we have already 

 had occasion to describe, for cultivating yeast in wort after 

 it has been for a longer or shorter time in the sweetened water. 

 The success of these methods of purification is mainly due to 

 the fact that wort is highly aerated, and experience shows that 

 the principal disease-ferments of beer are as much checked 

 in their development by the presence of air as they are favoured 

 by its absence, the inverse of which holds good in the case 

 of alcoholic ferments. So true is this that, working with 

 commercial yeast, which is invariably impure, it would be im- 

 possible in our opinion to make beer in closed vessels ; and, 

 indeed, as a matter of fact, one has never succeeded in doing 

 this, although the attempt has often been made. To do so 

 requires, much more than in methods actually in use, the 

 employment of pure yeast. 



There is, therefore, this advantage in cultivating yeasts in 

 shallow basins, that the multiplication of the alcoholic ferments 

 is promoted, and that of most of the disease -ferments is 

 checked. There is an exception, indeed, in the case of myco- 

 dermata ; but of all disease-ferments these are the most easily 

 got rid of, by repeating our growths before they make their 

 appearance. Notwithstanding this, our two-necked flasks, 

 which also contain much air at first, are to be preferred to 

 the shallow basins, inasmuch as they are a perfect safeguard 

 against the germs floating in the surrounding air, as well as 

 those of the ferment saccharomyces pastorianus. 



Another method is suggested to us by the curious results 

 of which we have already spoken, obtained by sowing yeasts 

 in a wort rendered acid and alcoholic by the addition of 

 bi-tartrate of potash and alcohol. Experience proves that 

 many disease-ferments find great diflSculty in withstanding 

 a succession of growths in wort to which 1| per cent, of 

 tartaric acid and from 2 to 3 per cent, of alcohol have been 

 added. Such a mixture, however, is equally well adapted to the 

 requirements of saccharom>/ces 2)cistori'anus, and we must always 



