24 MICRO-ORGANISMS AND FERMENTATION. 



problem is to maintain such large vessels in a condition of 

 absolute cleanliness. 



The experience of many years has, however, shown that 

 in breweries with open refrigerators and cooling apparatus, 

 open fermenting vats, and ordinary storage casks, a product 

 can be obtained with such a small content of harmful germs 

 that they have no practical influence on its quality, notwith- 

 standing the fact that the wort, especially on the refrigerators, 

 is exposed to a number of foreign germs. It has now been 

 proved that the harmfulness of the atmospheric germs in the 

 fermentation industry has been greatly exaggerated, for in 

 competition with the enormous number of yeast cells which 

 are established in the wort, the vast majority of these germs 

 never come to development. If it happens that, notwith- 

 standing the use of pure yeast, the product is strongly con 

 taminated with disease organisms, the explanation is, in the 

 great majority of cases, that these are developed in the plant 

 itself. It is from the surface of the different vessels employed 

 that the dangerous carriers of disease have developed, just 

 because a rational method of cleansing has not been adopted. 

 The chief importance must be attached to those stages in 

 the process where the liquid is longest under treatment, in the 

 fermenting vats and storage casks. In order to purify these 

 vessels, as well as the connections, disinfectants are almost 

 always used, and it may be remarked that a summary treat- 

 ment with these is not sufficient. This, at any rate, holds 

 good for wooden vats, in which it has often been proved that 

 notwithstanding disinfection the disease germs retain their 

 hold. A special investigation must, therefore, be made into 

 the physical character of the vessels, and the necessary pre- 

 cautions must be adopted. If in this way a rational method 

 is worked out, it will be found that the atmospheric germs 

 exercise no noticeable influence on the course of fermentation 

 or on the character of the product, since no opportunity is 

 given for them to establish themselves in the plant. 



Under special circumstances chemical reagents are used for 

 disinfection, the antiseptics. The ground work of the technical 

 application of antiseptics was laid by Schwann, who proved 

 in 1839 that yeast cells die under the influence of certain 



