STUDIES ON FERMENTATIOX. 365 



a greater quantity of oxygen than ordinary wort. In good 

 bre\yeries it is put apart by itself to ferment, and the yeast 

 which it yields is firmer and deposits more easily than that of 

 unfiltered wort. As for the fermentation, it is, under similar 

 conditions, quicker by a day or a day and a half than in the 

 case of ordinary wort. The difference in the quantity of 

 oxygen held in solution in the two kinds of wort is greater in 

 proportion as the external temperature is lower ; in winter it 

 may be twice as great as in summer. The reason is that in 

 summer a boiling wort does not obtain a minimum temperature 

 of 20° C. (68° F.), on the best coolers, in less than six or 

 seven hours. After leaving the coolers it is passed over a refri- 

 gerator. In winter it attains that temperature in about three 

 hours, or less, which then goes on sinking on the coolers. 

 During the last two or three hours which are employed in 

 bringing the temperature still lower, as also during the running 

 off, the wort absorbs an appreciable quantity of oxygen. In 

 other words, wort in winter remains for a longer time at low 

 temperatures, in free contact with air. 



Another circumstance unites with this exposure upon the 

 coolers to increase the aeration of the wort ; the wort is run into 

 the fermenting tuns through pipes of large sectional area, more 

 or less bent, and carries with it by suction considerable quan- 

 tities of air, which, from the continual agitation, gets well 

 Inixed with it. The effect of this mixing in the pipes is to 

 considerably increase the proportion of air in solution in the 

 wort, especially in winter, when the temperature of the wort is 

 lower ; and from the figures given below we may, althouo-h it 

 is very variable, put the average increase at a quarter of the 

 whole amount. The calculation has been made by comparing 

 the quantities of air held in solution in two samples of the same 

 wort, one of which was taken from the coolers at the moment 

 of "turning out,''* and the other from the fermenting vessel 

 after it was filled. 



* See foot-note, page 367. 



