Winemaking - What's in a grape?
Sugar - the yeast needs to get at this to convert it into alcohol and carbon dioxide.
Acids - there are two main acids in grapes, tartaric and malic. There is usually more tartaric acid than malic acid. Much of the tartaric acid gets right through the winemaking process, and gives the finished wine its freshness. After alcoholic fermentation a controlled process known as malolactic fermentation takes place during which tart-tasting malic acid is converted to softer lactic acid. The longer and more complete the malolactic fermentation, the softer and rounder the wine. Winemakers typically suppress the malolactic fermentation with sulphur dioxide if a more acidic, fresher-tasting wine is desired.
Water - it is the water from the pulp of the grape that we actually drink. Unlike in brewing, for example, no added water is needed in the winemaking process.
Grape pips contain bitter oils. For this reason, whatever is done in winemaking it is important to avoid crushing the pips.
The stalk contains woody tannins. Some winemakers still include the stalks in their fermentations to extract these tannins, as well as the tannins from the skins. However, the more normal practice nowadays is to de-stalk the grapes when they arrive at the winery.
Colour - the colour compounds, anthocyanins, are located in the skin of the black grapes. The anthocyanins need to be extracted from the skins to get the colour in red wines. By contrast, if the juice can be squeezed from the pulp with little skin contact, then white wine can be made from black grapes. Many of the great champagnes are made from a blend of Pinot Noir, Pinot Meunier (both black) and Chardonnay.
Tannins - these are the dry, astringent tasting compounds that are usually extracted from the grape skins at the same time as the colour. They are one of the elements which give some red wines their longevity.
Flavour - Many of the natural flavouring compounds occur in the grape skin or just below it.
Bloom - the greyish, waxy layer on the outside of the grape skin is called the 'bloom'. Naturally occurring wild yeasts are found in the bloom.