What is wine?

The juicy flesh of the grape berry contains flavour compounds and sugar, which, when combined with yeast, forms alcohol and carbon dioxide gas. Yeast occurs naturally, and yeast spores stick to the waxy ‘bloom’ on the surface of the grape berries, ready to convert the sugar as soon as the grape is crushed.

The fermentation process doesn’t begin until the grapes are crushed, because the grape skin keeps the yeast and sugar apart.

This is (in very simple form) the ‘Great Wine Equation’ SUGAR + YEAST = ALOCOHOL + CARBON DIOXIDE (+heat).

Fermentation is a gradual process, and the winemaker can decide to stop the reaction at any stage, to make a semi-sweet wine, an off-dry one or a completely dry wine. The carbon dioxide gas is allowed to escape from the fermenting tank when natural, or ‘still’ wines are being produced. When sparkling wine is made, the carbon dioxide is trapped and stored in the wine under pressure, to be released later in the form of tiny bubbles, or mousse, which gives the sparkling wine its seductive twinkle.

In South Africa the sugar content of a wine determines what the wine may be called. Sugar content is expressed in grams per litre, and, in order to get an idea of the actual quantity involved, remember that a teaspoon holds about 2,5 grams of sugar. One litre is the capacity of a large cold drink bottle (the standard wine bottle size, 750 ml, is of course three quarters that volume). The official sugar classification in South Africa is as follows:

Extra Dry: 2,5 gm/l or less
Dry: 4,0 gm/l or less
Off –Dry: 4 to 12 gm/l
Semi-sweet: 4 to 30 gm/l
Special Late Harvest: 20 – 50 gm/l
Noble Late Harvest: 50-plus gm/l (there are other requirements to be met with a Noble Late Harvest as well).

From this it can be seen that considerable leeway is allowed. A wine with 5gm/l, for example, could be called either a semi-sweet or a special late Harvest. A wine with 4gm/l could be anything from dry to semi-sweet. However for a wine to be called either off-dry or semi-sweet another factor enters the equation, which is acidity.
Off-dry wines with up to 9 gm/l of sugar must have no more than two grams less acid than sugar. Up to 12 grams of sugar the acid must not be less than 7 grams. If you have a wine that falls into the off-dry range (i.e between 4 and 12 gm/l) and you want to label it semi-sweet, then it must have less acid than the above figures.

But what does all this talk about sugar mean? The good news for slimmers is that
an extra dry wine will contain less than a teaspoon of sugar to a litre of wine—hardly worth worrying about. The bad news is that alcohol is about as high in kilojoules as sugar is.