Grape wine
Practical Action
the fermentation is active. You know the fermentation is over when no more gas is
produced.
The fermentation has to take place without oxygen (it is an anaerobic fermentation). If
oxygen gets into the system during the fermentation, the alcohol will be converted into
acid (this is what happens when you make vinegar, which is acetic acid). Wine that has
spoiled because it has been exposed to the air may taste very acidic.
There are lots of bacteria and yeasts around in the air and on the surface of the fruits.
They all have the potential to spoil the wine. It is extremely important that these
bacteria do not start to grow in the fermenting grape juice. Particular care must be
taken with the cleanliness of the equipment and personal hygiene.
All equipment must be sterilised with a solution of sodium or potassium metabisulphite
before it is used.
Production of red grape wine
Red grape wine is an alcoholic fruit drink of between 10 and 14% alcoholic strength that is
made from the fruit of the grape plant (Vitis vinifera). The colour ranges from a light red to a
deep dark red depending on the grape variety and the length of fermentation and maturation.
There are many varieties of grape used including Cabernet Sauvignon, Grenache, Nebbiolo, Pinot
Noir, and Torrontes. The skins of the grape are included in the production of red wine, to allow
for the extraction of colour and tannins, which contribute to the flavour.
Production of white grape wine
White grape wine is an alcoholic fruit drink of between 10 and 14% alcoholic strength that is
made from the fruit of the grape plant (Vitis vinifera).. The grape varieties used for making white
wine include the following: Airen, Chardonnay, Palomino, Sauvignon Blanc and Ugni Blanc.
White wine has a pale yellow colour. The skins are removed from the grapes before fermentation
begins.
The fermentation process is very similar for both types of wine:
Raw material preparation
Select healthy, ripe, undamaged grapes. The fruit should taste sweet, ripe and slightly tart. Make
sure they are ripe by squashing two handfuls, straining the juice and measuring the sugar level
with a refractometer if you have one available. The total soluble sugars should be about 22°
Brix, which is equivalent to a specific gravity of 1.0982 or 11% potential alcohol. Remove the
grapes from the stems (stems make the wine taste bitter). Discard any that are rotten or unripe.
Wash them well in clean water to remove dust. Crush the grapes to yield the juice plus skins,
which is known as must. Traditionally grapes are crushed in large open vessels by people
walking on them with bare feet. This really is not very hygienic and is not recommended. It is
preferable to use a sterilised potato masher or very clean hands.
Sterilise the equipment
It is essential to sterilise all the equipment before use. Wash the equipment in boiling water.
Use a solution of sodium or potassium metabisulphite to clean the fermentation vessel and the
bottles for storage. Add 3 tablespoons of potassium metabisulphite to 4.5 litres of water and
mix well. Rinse the bottles well with boiled water afterwards to get rid of any residual sulphite.
Processing
Red wine
Transfer the crushed grapes plus skins to a large fermentation vessel, such as a plastic bucket
with a lid. Seal the lid, place in a warm room (21-24°C) and leave to ferment for between 24
hours and three weeks. The ethanol produced during this initial fermentation helps with the
extraction of pigment from the skins. The longer the fermentation, the darker the wine.
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