214 



NATURE 



\7an. II, 1877 



of great interest to which we must again refer when con- 

 sidering the action of yeast upon sugar. 



In this germinating process we have an example of the 

 way in which insoluble matter stored up, whether in the 

 seed or in the tissues of a plant, becomes digested and 

 used for the production of fresh tissues. Th:s property 

 is not limited to vegetable organisms ; in animals, also, we 

 find stored-up matter, fatty or amylaceous, acted upon by 

 albumenoid ferments, and being thus rendered soluble, 

 become available for the building up of fresh structures, 

 or for the production of heat by their oxidation in the 

 system. It would lead us too far to discuss here the 

 manner and the agents by which albuminous food, such 

 as llesh meat, cheese, &c., are made soluble in the human 

 economy. Suffice it here to state that the means by which 

 nature produces the desired end of solution in animal and 

 vegetable alike, are moisture, heat, and albumenoid fer- 

 ments. 



The following analyses by Oudemans show the changes 

 produced in the malting process and in the subsequent 

 drying on the kiln :• — 



These analyses, though made some years since, and 

 differing in some points from our existing knovvledge, are 

 yet sufficient for our present purpose. We see tha* the 

 air- dried malt, when compared with the barley from which 

 it was made, is poorer in starch, and richer in woody 

 fibre. 



Again, as regards the changes in the albuminous bodies, 

 still quoting Oudemans, we find — 



We notice that there has been a loss of some of the albu- 

 minous matters in the germinating process, but at the 

 same time an increase in the soluble or active agents of 

 change, to obtain which the malting process is followed. 

 Let us now examine the changes which the malt under- 

 goes when placed in the brewer's mash tun and submitted 

 to the action of heat and water. In England the amount 

 of water employed varies with the nature of the beer to be 



made, it may be taken, however, as being about twice the 

 weight of the malt, and the temperature of the mixture of 

 malt and water varies from 63° C. to 67° C. In the course 

 of half-an-hour the insoluble starch is converted into 

 soluble sugars and dextrine. The infusion thus obtained 

 is, however, too dextrinous in character for the production 

 of dry alcoholic ales, but as the process continues, more 

 and more water is assimilated, and finally an infusion is 

 obtained rich in alcohol-yielding sugars. 



Many theoretical explanations have been given, and 

 will doubtless yet be given, as to the action and the 

 products formed. We are indebted to the admirable 

 and suggestive researches of O'SuUivan for the first clear 

 exposition of what takes place, or rather of one of the 

 changes which occur. He formulates the reaction thus : — 

 C18H30O15 + H'jO = CfiH^oOg + C12H22O11, 



iitarch Dextrine Maltose 



and he states that this is the final action of soluble fer- 

 ments on starch. This equation, however, expresses only 

 what takes place when a small quantity of malt acts on 

 starch paste at a temperature of only 40° C. to 45° C. 

 We must rather assume the probability of several changes, 

 of which that formulated by O 'Sullivan is one. Thus if 

 the amount of starch be large in comparison to the active 

 albumenoid ferments, and if the water and time of in- 

 fusion be lessened, we obtain a solution having a reducing 

 power on Fehling's liquid equal to 33 per cent, of glucose. 

 On the other hand, if the conditions be reversed, that is, 

 if we increase the time, the amount of ferment, and the 

 water, we obtain an infusion having a reducing power 

 equal to 66 per cent, of glucose. 



Here, however, the action ceases, and the so-called 

 diastase of malt is unable to carry on the hydration 

 beyond the point last-mentioned, where we obtain a solu- 

 tion which reduces Fehling's liquid to the extent of two- 

 thirds of the reduction obtained when the starch is fully 

 hydrated by weak mineral acids. 



Formulating the reactions according to the Fehling 

 reducing products obtained we should have — 

 Ci2H2oOj o + 2HaO 



this product having a 33"33 per cent, reducing action. 

 On the other hand, where we continue the action of 

 diastase for a longer period and with more water, we 

 have — 



CiaHjioOio + 2HaO 



Ci.H,oO,o + 2H,0 



C13H20O10; 



this product having a 66 '66 per cent, reducing power, 

 and being apparently the final action of diastase on 

 starch. When the hydration of the starch is effected by 

 dilute acid we obtain — 



Ci,H,oOio + 2H2O 



CisH.oO,, + 2HjO 



Ci-jHaoOie f 2HjO ; 

 that is, dextrose having the full reducing action. 



O'SuUivan's dextrine-maltose reaction might similarly 

 be thus expressed — 



Ci aHgoOjo + H,0 



ClaH.oOio + H.,Q 



Ci2HjoC)io 

 and giving a product having a 44*44 per cent, reducing 



A 



