The juice from black grapes is colourless - the colour, flavour and texture of red wine are derived from the skin, pips and stems. A winemaker aims for a balance of flavours and tries to add colour without overpowering the wine with too much tannin.
Harvest
One of the most important decisions the winemaker has to make is when to pick the grapes. Red grapes are usually picked later than white. The criteria for picking are the level of sugar, flavours and the ripeness of the stems and pips. When grapes have not reached full ripeness, unripe tannins can lead to a hard, stalky taste. Rain can change the quality and tends to dilute the grapes and increase the risk of mould.
Crush and destem
Grapes need to be lightly crushed to release their juices. The stems may be left or removed. The winemaker may retain the stems during fermentation for tannin and structure.
Fermentation
The fermentation process involves mixing the skin and the juice with yeast that may be added or occur naturally. The microscopic organisms convert sugar in the fruit to alcohol. Fermentation happens between 20 and 40 degrees Celsius. At the cooler end of the scale, the wine's fruity character will be enhanced. Higher temperatures are used to extract the colour, flavours and tannin from the skin and the pips. The winemaker can use a number of methods to extract flavour and tannin from the skins. This may involve people treading on the grape skins in the vat or the use of machines.