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Fermentation
This process acts on sugars and converts them into alcohols, at the same time transforming other constituents of fruit
into aldehydes, aromatics and a million things that give each wine its individual personality.
But the basic action of fermentation is to change sugar into alcohol.Glucose, the basic sugar, has the formula:
C 6H12O6,
or six atoms of carbon, twelve of hydrogen and six again of oxygen.
Scientists put it like this:
In the presence of yeast and in the right conditions, this just gets converted into
C2H5-OH, twice over,as well as two times CO2.
Well, C2H5OH is nothing but the potable, intoxicating ethyl alcohol and CO2 is carbon dioxide. So, during fermentation, the sugar becomes alcohol and carbon dioxide is given off. C6H12O6 -> 2C2H5OH + 2CO2.
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In the traditional method, the grapes are crushed, by treading underfoot, in a wide wooden tub, wooden because grape juice is acid and any metal coming into contact would react and contaminate the wine! The grape juice is then covered and left to ferment, with the skins still there, for a few days. |
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During this period, when the juice is in contact with air, the natural yeast on the grape skins multiplies a million-fold in
the rich nutrients of the grape juice. And the skins release their red colour, and their ‘bite’ of tannin, into the juice. There
is some fermentation, but the main thing in this phase is that the yeast multiplies.
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to continue with no more contact with air. For this, the juice to filled right to the top of a tall container, often fittedwith an ‘air lock’, which lets the carbon dioxide bubble out but not any air in! And the yeast, which is in good quantity, gets on with its main business of fermentation! it is run into bottles and lands on our table! |
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Sugar:
How much sugar?
For table wine with about 12% alcohol, one has to start with juice that contains about 225 grams of sugar
to the litre. The grapes in Europe have more than this and some water needs to be added. Traditionally, it
was considered very bad form to make up for poor grape by adding crystalline sugar to the juice. In fact,
doing this was an offence in France during periods of wine history.Jean-Antoine Chaptal, an accomplished chemist who also served in Napoleon's cabinet, did important work
in regulating the process of wine-making and the technique of adding crystaline sugar during bad seasons.
Addition of sugar to grape juice, which raised protests, both as a departure from tradition and also as
affecting the interests of vintners, is now known as 'Chaptalisation' and is allowed by
law only to a limited extent and subject to the vinyard having followed fair cultivation practices.
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Click to play Lina Margy's 'Ah, Le Petit Vin Blanc'
(Ironically, this joyful, classic, French drinking song was composed in 1943, a dark year in French history)
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