AIR AND WATER. 75 



for microbiological examination, in order that the micro- 

 organisms which appear may be more closely investigated 

 in regard to their action on wort and beer. For water analyses 

 in connection with distilleries and allied industries, sweet wort 

 is usually employed. This has been found to answer the 

 purpose well, and is easier to obtain clear after sterilising than 

 the mash i.e., the worts from distilleries and yeast manu- 

 factories. If special problems arise, as, for instance, the 

 presence of certain species of micro-organisms, the analytical 

 apparatus should be modified to suit the characteristics 

 of the particular species. Thus, for yeast factories, the 

 appearance of moulds and putrefactive bacteria will be of 

 special importance. Provision for the former can be made 

 by cultivation of the water on the surface of congealed gelatine 

 which has been mixed with a decoction of fruit, and for the 

 latter by employing ordinary plate - cultures consisting of 

 neutral nutrient gelatine. For special demonstration of the 

 Sarcina forms in beer a neutral decoction of yeast, with the 

 addition of a small quantity of alcohol, will be suitable. For 

 developing " wild yeast," wort may be used with an admixture 

 of hydrofluoric or tartaric acid, and so on. 



Experiments may also be arranged in connection with 

 other branches of the brewing industry by mixing the liquid 

 which is to be fermented with a certain quantity of the sus- 

 pected water at different stages of the fermentation, the 

 addition of pure yeast having been previously made. The 

 difficulty of this method when working with small quantities 

 consists, as is well known, in approaching sufficiently near to 

 practical conditions to make it possible to draw direct con- 

 clusions. If, as is the case in our own laboratory, it is 

 desired to ascertain what groups or species of organisms occur 

 in the water, then it will be of no consequence if the sample 

 has been delayed in transit. 



