VINOUS FERMENTATION. 



107 



us ereraacausis, that is, its conversion into 

 acetic acid, is prevented by the addition of a 

 small quantity of sulphurous acid. This 

 acid, by entering into combination with the 

 oxygen of the air contained in the cask, or 

 dissolved in the wine, prevents the oxidation 

 of the organic matter. 



The various kinds of beer differ from one 

 another in the same way as the wines. 



English, French, and most of the German 

 beers, are converted into vinegar when ex- 

 posed to the action of air. But this property 

 is not possessed by Bavarian beer, which 

 may be kept in vessels only half filled with- 

 out acidifying or experiencing any change. 

 This valuable quality is obtained for it by a 

 peculiar management of the fermentation of 

 the wort. The perfection of experimental 

 knowledge has here led to the solution of 

 one of the most beautiful problems of the 

 theory of fermentation. 



Wort is proportionally richer in gluten 

 than in sugar, so that during its fermenta- 

 tion in the common way, a great quantity 

 of yeast is formed as a thick scum. The 

 carbonic acid evolved during the process at- 

 taches itself to the particles of the yeast, by 

 which they become specifically lighter than 

 the liquid in which they are formed, and rise 

 to its surface. Gluten in the act of oxida- 

 tion comes in contact with the particles of 

 the decomposing sugar in the interior of the 

 liquid. The carbonic acid from the sugar 

 and insoluble ferment from the gluten are 

 disengaged simultaneously, and cohere to- 

 gether. 



A great quantity of gluten remains dis- 

 solved in the fermented liquid, even after the 

 transformation of the sugar is completed, 

 and this gluten causes the conversion of the 

 alcohol into acetic acid, on account of its 

 strong disposition to attract oxygen, and to 

 undergo decay. Now, it is plain, that with 

 its separation, and that of all substances ca- 

 pable of attracting oxygen, the beer would 

 lose the property of becoming acid. This 

 end is completely attained in the process of 

 fermentation adopted in Bavaria. 



The wort, after having been treated with 

 hops in the usual manner, is thrown into 

 very wide flat vessels, in which a large sur- 

 face of the liquid is exposed to the air. 

 The fermentation is then allowed to proceed, 

 while the temperature of the chambers in 

 which the vessels are placed is never allowed 

 to rise above 45 to 50 F. The fermentation 

 lasts from three to six weeks, and the car- 

 bonic acid evolved during its continuance is 

 not in large bubbles which burst upon the 

 surface of the liquid, but in small bubbles 

 like those which escape from a liquid satu- 

 rated by high pressure. The surface of the 

 wort is scarcely covered with a scum, and 

 all the yeast is deposited on the bottom of 

 the vessel in the form of a viscous sediment. 



In order to obtain a clear conception of 

 the great difference between the two kinds 

 of fermentation, it may perhaps be sufficient 

 to recall to mind the fact, that the transform- 



ation of gluten or other azotised matters is 

 a process consisting of several stages. The 

 first stage is the conversion of the gluten 

 into insoluble ferment in the interior of the 

 liquid, and as the transformation of the su- 

 gar goes on at the same lime, carooaic acid 

 and yeast are simultaneously disengaged. 

 It is known with certainty, that mis iorma~ 

 tion of yeast depends upon oxygen being 

 appropriated by the gluten in the act of de- 

 composition ; but it has not been sufficiently 

 shown whether this oxygen is derived from 

 the water, sugar, or from the gluten itself; 

 whether it combines directly with the glu- 

 ten, or merely with its hydrogen, so as to 

 form water. For the purpose of obtaining 

 a definite idea of the process, we may de- 

 signate the first change as the stage of oxida- 

 tion. This oxidation of the gluten then, 

 and the transposition of the atoms of the 

 sugar into alcohol and carbonic acid, are 

 necessarily attendant on each other, so that 

 if the one is arrested the other must also 

 cease. 



Now, the yeast which rises to the surface 

 of the liquid is not the product of a com- 

 plete decomposition, but is oxidised gluten 

 still capable of undergoing a new transform- 

 ation by the transposition of its constituent 

 elements. By virtue of this condition it has 

 the power to excite fermentation in a solu- 

 tion of sugar ; and if the gluten be also pre- 

 sent, the decomposing sugar induces its 

 conversion into fresh yeast, so that, in a cer- 

 tain sense, the yeast appears to reproduce 

 itself. 



Yeast of this kind is oxidised gluten in a 

 state of putrefaction, and by virtue of this 

 state it induces a similar transformation in 

 the elements of the sugar. 



The yeast formed during the fermentation 

 of Bavarian beer is oxidised gluten in a slate 

 of decay. The process of decomposition 

 which its constituents are suffering, gives 

 rise to a very protracted putrefaction (/er- 

 mentation) in the sugar. The intensity of 

 the action is diminished in so great a degree, 

 that the gluten which the fluid still holds in 

 solution takes no part in it ; the sugar in 

 fermentation does not excite a similar state 

 in the gluten. 



But the contact of the already decaying 

 and precipitated gluten or yeast causes the 

 eremacausis of the gluten dissolved in the 

 wort ; oxygen gas is absorbed from the air, 

 and all the gluten in solution is deposited as 

 yeast. 



The ordinary frothy yeast may be removed 

 from fermenting beer by filtration, without 

 the fermentation being thereby arrested ; but 

 precipitated yeast of Bavarian beer cannot 

 be removed without the whole process of its 

 fermentation being interrupted. The beer 

 ceases to ferment altogether, or, if the tem- 

 perature is raised, undergoes the ordinary 

 fermentation. 



The precipitated yeast does not excite or- 

 dinary fermentation, and consequently is 

 quite unfitted for the purpose of baking ; but 



