The Wine Press and the Cellar: A Manual for the Wine-Maker and the Cellar-Man

by Emmet H. Rixford

J. J. Griffin quotes Pasteur, and estimating the average loss to be 4½ per cent. of the sugar, deduces the figures .4881 as the per cent. by weight of alcohol produced by 1 per cent. of grape sugar. Dubief says that it takes 1.7 per cent. of cane sugar to produce 1 per cent. of alcohol by volume. Mr. Joseph Boussingault gives his experiments on musts fermented in small vessels under conditions similar to those under which fermentation is carried on in wine making on a large scale; and the result of his researches is that the product in alcohol is about 90 per cent. of what the chemical theory calls for: say, .46 by weight for 1 of sugar, or 1.7 + glucose for 1 per cent. of alcohol by volume. Mr. M. Boussingault gives it as the result of his experiment, that it takes 1.8 per cent. of sugar to produce 1 per cent. of alcohol.

So that it is pretty safe to say that it takes on an average about 1.8 of sugar to make 1 of alcohol, making some allowance for loss by evaporation, etc.

As has already been stated in the chapter on Musts, 1 per cent. for every 12 should be deducted from the percentage of sugar shown by the hydrometer for other matters than sugar.

If, therefore, we have a must which shows 24° by the saccharometer, we will deduct two, and call the remainder 22, sugar. Although it is not strictly correct to say that 22 divided by 1.8 will give the per cent. of alcohol which may be expected after fermentation, owing to the well known variation between per cent. by weight and by volume, as the figures increase, yet it is sufficient for all practical purposes.

Let us then divide 22, the supposed sugar in the must, by 1.8, the amount required to produce 1 per cent. of alcohol, and we obtain 12 and a fraction. Now the total indication by the saccharometer was 24 per cent.; if we divide this by two we get the same result in round numbers.

Hence the rule: one-half of the figure indicating the total per cent. by the saccharometer (hydrometer) is approximately the per cent. of alcohol to be expected in the wine.

Owing to the fact that the loss by evaporation and degeneration may vary greatly in different cases, this will be only a rough estimate, but it will prove as satisfactory as any method that can be adopted, and it corresponds very closely with the statement made by N. Basset, that in actual practice, a must of 20 per cent. gives only 7.88 per cent. of alcohol by weight, which corresponds with 10 per cent. by volume, nearly; and it is the rule given by Petiot and Dr. Gall for a natural must.

It seems, however, from what follows below, that this is only true of a normal must, but that a different rule applies to one of a very high degree of sugar.

Limits of Sugar and Spirit.—It is said that when a solution or a must contains over 35 per cent. of sugar, it will not ferment; nor will a wine or other alcoholic mixture which contains 20 per cent. of spirit ferment. Boireau says that the maximum of alcohol which a wine can attain by the fermentation of the richest must is between 15 and 16 per cent., and those wines which show a higher degree have been fortified. He says that the highest degree of spirit ever observed by him in a natural red wine was 15.4 per cent., when it was a year old; from that time the strength diminished, but the wine always remained sweet.

There is, however, a remarkable case given, and which seems to be well authenticated, of an Australian wine which contained naturally, by fermentation, 32.4° of British proof spirit, which is equal to about 18.21 per cent. And Vizitelli states that Mr. Ellis, of the firm of Graham & Co., asserts that perfectly fermented Alto Douro wine will develop 32° proof spirit, or 18 per cent. of alcohol, and when made exclusively from the Bastardo grape, as much as 34°, or about 19 per cent. of spirit. And Mr. Vizitelli adds that he is satisfied from what he saw at Jerez, that sherry wines which have had merely 1 or 2 per cent. of spirit added to them will in the course of time indicate 34°. To produce these results would seem to require more than 35 per cent. of sugar, according to our rule; but while it is approximately correct to say that 2 per cent. of sugar produces 1 per cent. of alcohol as long as we are dealing with a must of 24 or 25 per cent. and under, it may not be true of a must of 30 to 35 per cent., for the other solid matters probably do not increase in proportion to the sugar. Therefore, to reconcile this high degree of alcohol with the statement that a must containing over 35 per cent. of sugar will not ferment, we must use Pasteur’s figures, and then we will find that by them 35 per cent. of sugar is capable of producing over 20 per cent. of alcohol.