DESTROYING GERMS BY DRY HEAT 79 



drawn from the storage cask and sent out to the purchaser. Under normal 

 conditions this clarification is effected in sufficient degree in the storage cask, and 

 recourse should therefore be had to the filter only in such cases where, by reason 

 of defective treatment or other unfavourable circumstances, a turbid lager beer is to 

 be made similar to a beer of standard quality. Such was the practice in Bavaria 

 until a few years ago ; but since the great breweries in that country began to 

 cater for the export trade, they have had to conform to the tastes of their foreign 

 customers, who judge the quality of beer by the eye, and would, without having 

 tasted it, set it down as inferior if it were not perfectly bright. Therefore, in 

 order to render it acceptable to this large and continually increasing clientele, the 

 beer has to be passed through the filter. The South German connoisseurs in beer, 

 who judge their beverage by the flavour, raised objections, and with reason, 

 since nitration causes apart from the exception aforesaid an uncalled-for 

 depreciation of quality. This applies primarily to the chemical composition, the 

 filter removing from the beer sundry mucoid substances, extremely minute in 

 quantity and of as yet undetermined composition, but which, nevertheless, 

 contribute to the fineness of the flavour, so that an experienced palate can 

 distinguish with certainty between a filtered and unfiltered beer. This defect, 

 regretted though it be by connoisseurs, is, however, the lesser evil when compared 

 with the dangers, from a biological point of view, that are obviated by filtration. 



Two main types of beer filters are in general use. The one constructed by 

 Enzinger consists chiefly of a number of chambers, the walls of which are com- 

 posed of perforated plates lined with thick filter-paper, specially prepared for 

 the purpose, and through which the beer is forced by compressed air acting on 

 the storage cask. The second type of filter, recommended for brewery work by 

 Stockheim, contains as its acting ingredient purified (and therefore tasteless) 

 cellulose of a felty nature. No objection can be raised against the use of such 

 appliances in exceptional cases, since by this means a clear filtrate is obtainable 

 when all other methods of clarification have failed to remedy turbidity. This 

 decision must, however, be amended when it is a question of beer already in 

 good condition, this latter often suffering, under such treatment, a considerable 

 alteration (in certain circumstances) with regard to its flora, apart from the 

 depreciation of flavour already alluded to. The filter removes the yeast 

 cells, but allows the (much smaller) bacteria to slip through, so that the latter 

 appear in almost their original numbers in the filtrate, where, moreover, they 

 have free play, owing to their previous competitors, the yeast cells, having been 

 got rid of. This unfavourable modification in the relative condition of the two 

 classes of organisms becomes especially objectionable when a filtering material 

 that has already been in use before is employed, without- having been sufficiently 

 purified in the interim. In this manner the filtrate can be actually enriched 

 with bacteria, as the author ascertained by experiments with the Enzinger filter 

 in 1894. 



Respecting the wine filter in continually extending use in cellar management, 

 a full report can be perused in the handbook issued by BABO and MAOH (I.). 



76. Destroying- Germs by Dry Heat. 



Strictly speaking, the term " germ-free " should be applied only to such objects 

 as have actually been devoid of germs from the beginning or have been brought 

 into this condition by filtration. In the language of bacteriological practice, 

 however, it is also applied to objects wherein all the germs have been destroyed 

 and are only present in a defunct condition. Hence it would be more correct to 

 say that the object in question is " free from living germs," but this distinction, 

 being practically unimportant, is not generally drawn. 



