76 SACCIIAKOMVCES LESS. 



is then found to be no longer sweet but to have acquired' 

 what we know as an alcoholic or spirituous flavour. Analysis 

 shows that the sugar has nearly or quite disappeared, while 

 a new substance, alcohol, has made its appearance. The 

 sweet-wort has, in fact, been converted into beer. 



Expressed in the form of a chemical equation what has 

 happened is this : 



C H 12 6 = 2(C 2 H G 0) + 2(CO,) 



Grape sugar. Alcohol. Carbon dioxide. 



One molecule of sugar has, by the action of yeast, been 

 split up into two molecules of alcohol which remain in the 

 fluid, and two of carbon dioxide which are given off as gas. 

 This is the process known as alcoholic fermentation, 



It has been shown by accurate analysis that only about 

 95 per cent, of the sugar is thus converted into alcohol and 

 carbon dioxide : 4 per cent, is decomposed, with the for- 

 mation of glycerine, succinic acid, and carbon dioxide, and 

 i per cent, is used as nutriment by the yeast cells. 



For the accurate study of fermentation the sweet-wort of 

 the brewer is unsuitable, being a fluid of complex and un- 

 certain composition, and the nature of the process, as well 

 as the part played in it by Saccharcmyces, becomes much 

 clearer if we substitute the artificial wort invented by 

 M. Pasteur, and called after him Pasteur's solution. It is 

 made of the following ingredients : 



Water, H 2 O 83-76 per cent. 



Cane sugar, CjgH^Ojj ....'.. 15-00 

 Ammonium tartrate (NH 4 ). 2 C 4 H 4 O . rco ,, 



Potassium phosphate, K 3 PO 4 .... 0-20 ,, ,, 

 Calcium phosphate, Ca 3 (PO 4 ).> . . . 0-02 ,, 



Magnesium sulphate, MgSO 4 .... 0*02 ,, ,, 



lOO'OO 



