31: STUDIES ON FERMENTATION. 



that a few minutes' boiling renders liquids, and more especially 

 wort, absolutely free from liability to change when in contact 

 with pure air, that is, air which contains none of the germs of 

 organisms that are continually floating about in the atmo- 

 spheie. 



What is true in the case of wort is equally so in the case of 

 all organic liquids ; there is not a single one that could not 

 be rendered inaccessible to any subsequent change if it were 

 brought, first of all, to a suitable temperature, which would vary 

 with the nature of the liquids. Amongst them there are some 

 which, like vinegar, lose their tendency to change after having 

 been rapidly raised to a temperature of not more than 50° C. 

 (122° F.) ; others, like wine, require a greater heat. "Wort, 

 to which no hops have been added, should be subjected to a 

 temperature of not more than 90" C. (19-1° F.) ; milk to about 

 110° C. (230° F.).* 



It is easy to show that these differences in temperature, which 

 are required to secure organic liquids from ultimate change, 

 depend exclusively upon the state of the liquids, their nature, 

 and, above all, on the conditions that affect their neutrality, 

 whether towards acidity or alkalinity ; for it is not difficult to 

 observe that the least changes in these respects lead to consider- 

 able variations in the temperatures which we must employ. t 

 We could adduce many examples of this. The only diflference 

 between the nature of must and that of wine is caused by 

 fermentation. We may say the same thing of wort and beer, 

 and, better still, of new milk and sour milk. Must, to be 

 secured from change, requires a much higher temperature than 

 wine does ; similarl}^, wort requires a much higher temperature 

 than beer. Milk must be heated to about 110° C. (230° F.), as 

 we have just stated, but sour milk would require 20° C. or 30° C. 



• We have heard of liquids even less sensitive than these, which re- 

 quired a temperature of 120° C. (248° F.) or more, hut we have had no 

 opportunity of studying them. 



t See Pasteur, Memoire sur les Generations dites Spontanees {Annalea 

 dc Chiviie et de Physique, t. Ixiv. Z' serie, annee 1862). 



