CAPE WINE-LEVURES. 235 



li we now put the amount of carbon-dioxide formed by 

 fermentation and still kept inside the flask dissolved in the wine 

 and standing above it, at 1.5 grammes, then we should have to 



.. 1-5 46 51- 46 10 



add 4 x 44 g ramm es = . x — x - ccm . = 0-49 ccm. 



alcohol per 100 ccm. wine to the value calculated. 



In other words, the average difference between the calcu- 

 lated and the actually found alcohol-values will be eliminated by 

 assuming each flask to contain about 1.5 grammes of carbon 

 dioxide formed by fermentation, which is quite a reasonable 

 assumption. This point will be examined during my further 

 research on this subject. 



The above at any rate tends to show that the relative 

 amounts of carbon dioxide and alcohol formed during a pure 

 vinous fermentation are in accordance with the equation already 

 quoted, namely. 



C H H lL ,0,i = 2CO., + 2C. 2 H O 

 invert sugar = carbon dioxide -f- ethyl-alcohol 



It is at present impossible to explain the three exception- to 

 the above, namely, HeAi, PB3 and GBi. 



(4) Since the must used contained about 258 grammes sugar 

 per litre, we see that the good wine-levures formed 10 ccm. 



2SS '^SS 



alcohol out of t^o, 7 ■< 10 till 1 ^ 7 . x 10 grs sugar (the wines had 



15.70 - [6.37 volume per cent, alcohol) or 10 volume per cent, 

 alcohol in the wine was formed out of 158-164 grs. sugar per litre 

 of must. In Europe the reckoning is usually 10 volume per cent, 

 or degrees of alcohol for 170 grs. sugar per litre of must. The 

 figures obtained with these levures in cellar experiments will be 

 given in the next part of this paper. According to the above 

 equation 46 grs. or 57.5 ccm. alcohol are formed from 90 grs. 

 sugar, hence 100 ccm. alcohol or 10 volume per cent, are formed 

 from 156.5 grs. sugar. 



In actual practice this figure is never quite reached, since 

 the living levures form in addition to alcohol also several other 

 products, such as glycerine, succinic acid, volatile acids, apart 

 from the sugar which they consume as food. The amount to be 

 allowed for this is usually about 5%. so that it is considered that 

 the above fermentation holds good for about 95% of the total 

 sugar in the must. 



In the experiments here related the following percentages of 

 total sugar were thus decomposed : 



Let x be the percentage sought. 



Then in case of the wine with 15.70 volume per cent, alcohol 



x X 258 . . 1 t 1 



we have — grs. sugar giving 157.0 ccm. alcohol. 



x X 258 grs. 

 Hence 100 ccm. alcohol were found out of _ — 



sugar. 



