THE alcohol which we seek as an ingredient of our wine is a by-product of the yeast's process of self-reproduction.

When the yeast is put into a sugary solution, it begins to multiply vigorously, and in the complex chemical processes which ensue, the sugar is converted roughly half to alcohol by weight and half to carbon dioxide—the babbles in your beer, wine, cider or champagne.

It is an encouraging thought that for every bubble you see in your wine there is an equal weight of alcohol! The fermentation will be in two stages, but there is no distinct dividing line. The first, the aerobic ("with air") fermentation, will be comparatively vigorous, perhaps with some froth, but may last only five or six days. The wine will then settle down to the secondary, anaerobic ("without air") ferment, which will be much quieter and which towards the end may be barely discernible. This may last two, three or four months, or even longer.

Temperature plays an important part. Above 100 deg. F. (38 deg. C.) the yeast will certainly be killed; at too low a temperature it will ferment only very slowly, if at all. A fermentation should be started off at about 70 deg. F. (21 deg. C.), the secondary fermentation should be at about 60 deg. F. (16 deg. C), and the finished wine should be stored at 50 deg. to 55 deg. F. (10-13 deg. C). So the temperatures are easy to remember—70, 60, 50 F. (or 20, 15, 10 C.). A slow, quiet fermentation usually produces better wine than a fast, over-vigorous and short one, and there is no need to be fussy within 5 degrees F.

During the secondary fermentation it is wise to employ a device called a fermentation trap, or air lock, which both cuts off the air supply to the yeast and protects your wine from bacterial infection, of which more later.

As the fermentation proceeds, so the alcohol content increases, until finally it reaches a concentration (usually about 16-17% alcohol by volume) which is such as to inhibit the yeast, preventing any further activity. Any sugar still left in the wine then remains only as a sweetening agent. Once the fermentation is finished the wine will not normally become any stronger no matter how long it is kept, although it will undoubtedly mellow with maturity. So discount all the stories you hear on the lines: ". . . and this wine was 40 years old; it had become as strong as whisky!"

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