FERMENTATION 343 



the fermentation induced by them. If this lactic fermentation be allowed to spend 

 itself, the ferment appears to degenerate into the butyric form, and butyric acid is the 

 product, carbonic anhydride and hydrogen being evolved. 



^Respecting the temperatures adjudged to be the best for favouring alcoholic fer- 

 mentation, this is a subject to which wo must give the most patient reasoning ; for, 

 although brewing is an art known and practised throughout the world from time im- 

 memorial, it is a curious circumstance, that in no part of the manipulation is there so 

 much diversity of opinion as upon this one point temperature ; but it is not to be 

 wondered at, when we take into consideration that it is upon the particularly nice at- 

 tainment of a peculiar flavour, that one beer is appreciated by some, and a totally 

 different one by others ; so we see that the ' right flavour ' varies with the palate of 

 the consumer, and that for its attainment we have to rely almost entirely upon the 

 due proportion of the various products of fermentation. This no doubt explains to 

 some extent the cause of the different temperatures that are in favour with different 

 brewers. But there is another circumstance that it will be well to consider. It is, 

 perhaps, much to bo regretted that the chemists who have given us the results of their 

 researches have not considered it necessary to state the bulk of the material _ upon 

 which they operated in the prosecution of their experiments, for undoubtedly this cir- 

 cumstance has an important effect upon the temperature indicated ; the rate at which 

 the heat is generated, is transmitted by the vessel containing the fermenting wash, 

 and is absorbed or carried off by the surrounding medium, must have its effect upon 

 the thermometer's indications, and upon the resulting products of the fermentation. 

 In conducting a mash, we know that for the complete transformation of the starch 

 in a small mash, a considerably higher mashing-temperature is required than is ne- 

 cessary for a largo mash ; and by the same rule, fermentations must be conducted in 

 small vessels with a higher temperature than is required for larger vessels. But in 

 proportion as the yeast is subjected to the higher temperatures, or prolonged expo- 

 sure, so it degenerates both in vitality and character ; therefore it is best to maintain 

 a uniformly low temperature, and give the required impetus by an allowance of a 

 larger quantity of yeast. It would have been of considerable advantage to us as 

 brewers, if those gentlemen to whom we are so much indebted had stated the particu- 

 lar kinds of ferment that appeared to be mostly developed by the influence of the 

 temperature and time attendant on the fermentations which were the subject of their 

 researches ; but their investigations have, however, proved to us thus much : 



1. That alcoholic fermentation with ordinary brewer's yeast may be conducted with 

 a temperature so low even as 40 Fahr. 



2. That alcohol in the presence of gluten or yeast at temperatures above 52 is liable 

 to become acetic. 



3. That at temperatures above 61 the germs of lacteous ferment begin to show 

 vitality. 



4. That at temperatures above 84 alcoholic fermentation ceases, and lactic fermen- 

 tation degenerates into the butyric formation. 



In apportioning the quantity of yeast to a brewing, the gravity of the wort must be 

 a first consideration. 



In practice we find that with different gravities it does not answer to apportion 

 yeast by the rule of proportion, taking gravity for the data of calculation, for the higher 

 gravities require a higher percentage to be allowed them than the lower gravities ; this 

 arises from two causes : 



1st. It is self-evident that, as soon as fermentation commences, the amount of 

 alcohol manufactured in a certain bulk of wort of a high gravity must bear a greater 

 proportion to that bulk than would the alcohol produced from the same bulk of wort 

 at a low gravity; and it is found that the presence of alcohol in a wort has the power 

 of arresting the progress of fermentation, the more effectually as the quantity present 

 bears a higher proportion to the bulk. Of course, therefore, this is more easily accom- 

 plished in worts of high gravities ; and, in order to carry on the attenuation in such 

 worts, an extra quantity of yeast must be allowed to meet this emergency. 



For this reason it is sometimes found necessary to supplement the first addition of 

 yeast to a brewing by another portion to be added when the fermentation appears 

 shiggish, before the full amount of attenuation is reached ; and it is a good plan at 

 this time to freshen up the vitality of the ferment by a slight addition of malt meal 

 well whisked up with it. 



2nd. If worts of different gravities be examined thirty-six hours after the setting-on 

 has occurred, it will be found that each pound of yeast added will have done the work 

 of attenuation at a greater rate in the lighter gravities than will be the case with the 

 heavier worts. This undoubtedly arises in a great measure from the presence in the 

 lighter worts of the larger proportion of albuminous constituents, and this condition 

 adds considerably to the energy of the fermentation. The increased percentage of the 



