Red Grape Wine

Product description - Red grape wine is an alcoholic fruit drink of between 10 and 14% alcoholic strength. The colour ranges from a light red to a deep dark red. It is made from the fruit of the grape plant (Vitis vinifera). There are many varieties of grape used including Cabernet Sauvignon, Grenache, Nebbiolo, Pinot Noir, and Torrontes (Ranken, Kill and Baker, 1997). The skins of the grape are allowed to be fermented in red wine production, to allow for the extraction of colour and tannins, which contribute to the flavour. The grapes contribute trace elements of many volatile substances, which give the final product the distinctive fruity character. In addition, they contribute non-volatile compounds (tartaric and malic acids) which impact on flavour and tannins, which give bitterness and astringency.

Raw material preparation - Ripe and undamaged grapes should be used. Red grapes are crushed to yield the juice plus skins, which is known as must.

  • Selection of grapes

Mature and undamaged grapes

  • Crushing

Traditionally manually, but now by crushers

  • Pre-fermentation

24 hours to three weeks depending on colour required

  • Removal of skin

Can add sulphur dioxide to inhibit wild yeasts

  • Fermentation

 

  • Maturation

Ageing to develop aromas and flavours

Flow diagram

Processing - The crushed grapes are transferred to fermentation vessels. The ethanol formed during this fermentation assists with the extraction of pigments from the skins. This takes between 24 hours and three weeks depending on the colour of the final product required.

The skins are then removed and the partially fermented wine is transferred to a separate tank to complete the fermentation. The fermentation can be from naturally occurring yeasts on the skin of the grape or using a starter culture of Saccharomyces cerevisiae in which case the juice is inoculated with populations of yeast. This approach produces a wine of generally expected taste and quality. If the fermentation is allowed to proceed naturally, utilising the yeasts present on the surface of the fruits, the end result is less controllable, but produces wines with a range of flavour characteristics (Fleet, 1998), (Rhodes and Fletcher,1966), (Colquichagua, 1994).

Traditionally, fermentation was carried out in large wooden barrels or concrete tanks. Modern wineries now use stainless steel tanks as these are more hygienic and provide better temperature control.

Fermentation stops naturally when all the fermentable sugars have been converted to alcohol or when the alcoholic strength reaches the limit of tolerance of the strain of yeast involved. Fermentation can be stopped artificially by adding alcohol, by sterile filtration or centrifugation (Ranken, Kill and Baker, 1997).

Some wines can be drunk immediately. However most wines develop distinctive favours and aromas by ageing in wooden casks.Packaging and storage

Traditionally wine was delivered to the point of sale in casks. The product is traditionally packaged in glass bottles with corks, made from the bark of the cork oak (Quercus suber). The bottles should be kept out of direct sunlight. During storage, wines are prone to non-desirable microbial changes. Yeasts, lactic acid bacteria, acetic acid bacteria and fungi can all spoil or taint wines after the fermentation process is completed.

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