395 



The chief characteristic of glucose, or uncrystallisable sugar, 

 compared with cane sugar, or " saccharose/' is that the former can 

 ferment, whereas cane-sugar, in order to ferment, has previously to 

 be turned into glucose. 



Another characteristic is that while cane-sugar can be turned 

 into glucose, this latter form of sugar has never yet been changed 

 into crystallisable sugar. The inventor of a process that would 

 achieve this would be worth more than all the mines of this country 

 put together. 



During the process of fermentation, " dextrose " is the first to be 

 acted upon by the yeast ; and if the wine is badly fermented, and 

 remains sweetish, it is "Isevulose," which is found to have remained 

 unchanged. 



During the process of fermentation the constituents of glucose, 

 properly diluted, are split up into substances differing from it, both 

 in their physical and in their chemical properties, the products of 

 fermentation being carbonic acid gas and alcohol, besides other 

 bodies such as glycerine and succinic acid, which occur in small 

 quantities, and which varv in some measure with the temperature 

 in the vat during fermentation ; the glycerine giving mellowness 

 to the wine, while the succinic acid gives it that peculiar taste known 

 as "vinosity." 



Acids. Besides these two important ingredients, viz., w r ater and 

 sugar, the must of the grape contains small proportions of acids, 

 such as tartaric acid, which occurs to a large extent in the veget- 

 able kingdom ; malic acid, or the acid found in apples ; and tannic 

 acid or " tannin" ; and cream of tartar, which is an acid salt. 



The presence of these natural acids in must is most important. 

 A due proportion ensures a sound fermentation, being beneficial to 

 the healthy growth of the pure wine yeast, and injurious to that of 

 germs of maladies. Good fermentation ensures good keeping 

 qualities. Acids also fix the colour of wines, which otherwise 

 would by degrees be cast in the lees. Too much acidity, however, 

 makes the wine tart and raw ; too little makes it mawkish, and causes 

 it to get flat. 



The right amount of acidity in must varies according to the 

 class of wine. Its measure is sometimes expressed as equal in 

 strength to sulphuric acid, and sometimes to tartaric acid, and as 

 authors seem to use these two standards indiscriminately, it is 

 useful to bear the following rule in mind : 



To convert sulphuric acid into tartaric acid, x 1'53. 

 To convert tartaric acid into sulphuric acid, +O65. 



Thus, must producing the best claret contains acids equivalent 

 to 4 to 6 pro mille. of sulphuric acid, or 6 to 9 pro mille. of tartaric 

 acid. 



