STUDIES ON fer:mentatiox. 351 



tun, whicli is 3 or 4 metres (10 or 12 feet) in depth ; this the 

 brewer, by means of a cord, can lower into the tun and pull up 

 again at will, giving it a kind of see-saw movement which 

 agitates the surface of the liquid and aerates it. The use of 

 the fermenting tun itself and the racking of the wort from that 

 tun into casks have the effect of aerating the beer and the yeast, 

 and imparting to the latter a greater vigour and activity. 



The resumption of fermentation in cask, after the beer has 

 been run out of the tuns in " low " fermentation breweries is, in 

 our opinion, principally due to the aeration of the beer at the 

 moment when it is racked. The brewer ought to bear in mind 

 that, during racking, every detail is of importance ; it makes a 

 great difference whether when the beer is run into the casks it 

 falls from a height or is conducted by a tube to the bottom of 

 the casks, whether it passes directly into the casks, or is poured 

 into them from buckets, and whether it runs in a stream of small 

 or large diameter, since these different methods cause the intro- 

 duction of corresponding different quantities of air into the beer. 



We have devised a simple arrangement for bringing the 

 fermenting liquid into contact with various proportions of 

 atmospheric air. Appended is a sketch of this apparatus (Fig. 

 80). Instead of one tube serving alike for the entrance and 

 escape of gas, there are two similar ones, each of which opens into 

 one of the tubulures on the cover. Round the other end of one 

 of the tubes is fitted a kind of muff or bag, composed of a cylin- 

 drical cage of metallic gauze, over which a layer of well-combed 

 cotton wool is placed, the whole being covered with a muslin 

 bag. The object of this arrangement is to act as an air-filter for 

 retaining the particles of dust. When fermentation has com- 

 menced in the apparatus, we have simply to press momentarilj'- 

 the india-rubber connection between the tube from the lid and 

 the tube with the bag. This will at once cause a regular stream 

 of carbonic acid to issue from the end of the uncovered tube, 

 whilst the air will enter by the filtering tube to take its place ; 

 and this arrangement will be maintained throughout the whole 

 course of the fermentation, even if we omit the precaution of 



