NA TURE 



213 



FERMENT A TION 



EtJides sur la Bilre. Par M. L. Pasteur. (Paris : 



Gauthier-Villars). 



I. 



IN a recent notice of an article on Brewing contributed 

 by Mr. Pooley to Stanford's "British Manufacturing In- 

 dustries," some statistics were quoted showing the gigantic 

 development which the production of beer has acquired in 

 the United Kingdom. The amount of beermanufactured in 

 the British Islands, vast though it be, forms yet but a small 

 portion of that made throughout the world. Probably no 

 industry — saving agriculture — employs sd large an amount 

 of capital as that of brewing and the various industries 

 supported by it. Important though this old and at pre- 

 sent vastly extended industry be, it is yet one which, until 

 ve recently, scientific methods of investigation had done 

 but little to add to our knowledge of the complex phenomena 

 underlying the apparently simple art, and therefore even 

 less in preventing the serious losses constantly occurring 

 even with the most careful manufacturer. 



The valuable contribution to our knowledge of the 

 biological aspect of fermentation, which M. Pasteur has 

 just given to the world, is a worthy sequel to the classical 

 researches described by the illustrious chemist in the 

 papers read before the French Academy during the last 

 fifteen years, and summarised by him in a popular form 

 in his " ifetudes sur le Vin," and " Etudes sur le Vinaigre." 

 TheseT important works, containing the results of long 

 years of laborious and brilliant research, have done much 

 to remove the charge brought against science, and have 

 indeed become to the brewer and wine-grower as the 

 brightening sky to the mariner groping his way in fog 

 and uncertainty to his haven. The grateful recognition 

 of twenty years fruitful labour is due alike from practical 

 and scientific men to the illustrious investigator of the 

 Biology of Fermentation, and he certainly will not deem 

 it the less hearty and sincere if occasional exception here 

 or elsewhere be taken to some of his propositions. 



Before considering Fermentation and the recent views 

 promulgated by Pasteur and others regarding the inter- 

 esting and complex phenomena grouped under this term, 

 it will be useful to discuss the changes produced in the 

 malting and mashing processes of the brewer as neces- 

 sary precursors to the greater change produced in Fer- 

 mentation properly so-called. Let us, then, examine the 

 change brought about by the action of water arid heat on 

 the grain of any of our common cereals — barley, for 

 example ; if this be ground and digested for a few hours 

 at a temperature of 60° C. with five or six times its weight of 

 water, it will be found that the whole, or nearly the whole 

 — this depending upon the comparative activity of the 

 albuminous matters present— of the insoluble starch will 

 be changed into products soluble in water. By the agency 

 of the albuminous ferments or alterative agents water will 

 be assimilated and dextrine and Glucose and products of 

 transformation intermediate between these will be ob- 

 tained. 



This reaction is general, and applies not only to the 

 grain of our common cereals, but also to other stored-up 

 Vol. XV. — No. 376 



amylaceous vegetable products. While, however, the 

 agency of heat and moisture suffice to bring about this 

 remarkable change, it yet requires too much time, and the 

 products formed are not well adapted to the brewer's 

 wants. Various albumenoid bodies, such as the ptyalin 

 in the saliva, and those in the secretions from the pan- 

 creas and intestinal canal in the animal economy in- 

 tensify the action of the soluble albumenoids in ordinary 

 bread-stuffs, and hence produce a greater hydration, and 

 therefore solution, in a given time. Now the object of 

 malting is to convert some of the inert albumenoids into 

 these more active agents of change, and thus the maltster 

 avails himself of a property existing throughout all vege- 

 table tissues, whereby previously stored-up insoluble 

 amylaceous matter is converted, through the joint agency 

 of moisture, heat, and albumenoid ferments, into soluble 

 sugars, and used along with soluble albumenoid matters 

 for the production of new tissues. 



To produce an increase in the albumenoid ferments in 

 barley — the grain chiefly employed in England— the 

 maltster first steeps the grain in water for a period varying 

 from fifty to seventy hours according as the skin is thin 

 or thick, that is, more or less pervious to water. So soon 

 as the desired amount of water has been absorbed, it is 

 removed from the cistern and spread out on the floor of 

 the malt-house, the temperature best suited for the pro- 

 duction of sound malt being about 15° C. The germina- 

 tion of the grain commences and is allowed to proceed, 

 with occasional turnings, until the plumule of the young 

 growing plant has advanced far enough up the back of 

 the grain to satisfy the objects which the brewer may 

 have in view. Thus, if a full and somewhat dextrinous 

 ale be required, the plumule is barely allowed to grow to 

 the bend, or bridge, of the grain, whereas, if a dry alcoholic 

 ale be required, the growth is allowed to proceed further. 

 According to the growth of the plumule, so does the pro- 

 duction of active ferment vary. This point being obtained, 

 the malt is placed on the floor of a kiln, whereby further 

 growth is stopped. Without dwelling with too much de- 

 tail on this malting, or germinating, process, it will be 

 useful to consider here some of the changes produced. In 

 the first place, by the absorption of water the grain swells 

 and the albumenoid ferments previously existing in the 

 grain are made soluble, and these, by the aid of moisture 

 and heat, begin to act on the starch. Meanwhile, a por- 

 tion of the insoluble albuminous bodies are rendered 

 soluble, and aid in this conversion of starch, and at the 

 same time, in conjunction with the transformation pro- 

 ducts of starch, serve to build up the cell structures of the 

 growing plumule and rootlets. Throughout the germinat- 

 ing process carbonic acid and heat are evolved precisely as 

 in the subsequent process of the conversion of sugar into 

 alcohol. The analogy does not, however, rest here, 

 because alcohol is also produced in small quantities. If 

 the growing grain be shut in an air-tight vessel, it will be 

 found that as the growth of the young plant is stopped, 

 the amount of alcohol becomes largely increased, attended 

 at the same time by the production of a large quantity of 

 gas, the chief constituent being carbonic acid. This pro- 

 duction of alcohol by vegetable cells has already been 

 noticed in the case of fruits by Lechartier and also by 

 Pasteur. The enormous volume of carbonic acid gas 

 produced without the intervention oi free oxygen is a fact 



M 



