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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 use- 
ful to bear the following rule in mind:— 
To convert sulphurie acid into tartaric acid, < 1.53. 
To convert tartaric acid into sulphurie acid, X< 0.65. 
Thus, must producing the best claret or light wine contains 
acids equivalent to 4 to 6 pro mille. of sulphuric acid, or 6 to 9 pro 
mille. of tartaric acid. 
Heavy sweet wines are made of grape must showing an acidity 
of 3 to 4 pro mille. expressed as sulphuric acid, or 4.6 to 6 as tar- 
tarie acid. 
Brandies of the best kind are generally made of wines rather 
bigh in natural acidity, and manufactured from must going 6 to 
9 pro mille. as sulphuric acid, or 9.2 to 13.8 as tartaric acid. 
Should the acidity fail to come up to the standard desirable 
for the class of wine to be manufactured, it is not only permissible 
but advisable to supplement the difference by— 
1st. An adequate addition of pure crystals of tartaric acid. 
For this purpose every 1 per mille. may be calculated as Ib. 
per 100 gallons of must. Thus, if a shiraz or a malbee shows 5 
per cent. of must acidity, caleulated as tartaric acid, it is desirable, 
to bring that must up to 7 per cent., to add 2lbs. of tartaric acid 
ervstals for every 100 gallons. 
For that purpose it is best to sprinkle the acid erystals over 
the grapes as they come out of the crusher. 
The tartaric acid then combines with the potash salts in the 
must, and, after it has directed its influence in a beneficial manner 
during the course of fermentation, it settles down as tartar. 
Some wine makers prefer, when. it is found necessary to raise 
the degree of acidity of a must, to use a mixture in equal parts of 
cream of tartar and of tartaric acid. The resulting wine is less 
astringent and raw. 
The belated addition of tartaric acid to made wine fails, it is 
obvious, to have a beneficial influence on the fermentation, and im- 
parts to the wine a raw and acerb taste. 
