Grape wine
Practical Action
Remove the skins and transfer the partially fermented wine to a separate tank to complete the
fermentation. Add yeast to the fermenting grape must, close the top of the fermentation vessel
with an airlock that contains water, place in a warm place (21-24°C) and leave to ferment until
all the sugar has been converted to alcohol or the alcohol content of the wine has reached a high
enough level. You know this has happened when the bubbles stop appearing in the water in the
air lock. You can measure the specific gravity of the wine with a hydrometer. This gives an
indication of the amount of alcohol that is present.
White wine
Strain the extracted grape juice into a fermentation bucket. Add the wine yeast, seal the
fermentation vessel and leave in a warm place (12-18°C) for 7 to 14 days to ferment. The low
temperature and slow fermentation encourages the retention of volatile compounds which give
the wine flavour.
Adjusting the Juice
Controlling the acidity, sugar content and temperature of the juice (must) are all critical to
producing good quality wine.
The acid content can be measured using a titration kit. The ideal acid content is 6 to 7 grams
per litre for dry reds and 6.5 to 7.5 grams per litre for dry whites. If the acidity is to low, add
tartaric acid (in very small amounts) until the acidity reaches the desired level.
The sugar level should be about 22° Brix for both red and white wines. If it is lower than this,
increase it by adding a sugar syrup to the juice. Make the sugar syrup by dissolving one cup
sugar into one-third cup of water. Bring it to a boil in a saucepan and immediately remove from
the heat. Cool before adding in small amounts, one tablespoon at a time, until the desired
degrees Brix is reached. To lower the sugar level, simply dilute the must or juice with water.
The temperature of the must should be adjusted to provide optimum conditions for the yeast to
grow. The optimum temperature of the juice is about 22-24°C for red wines and 12-18°C for
white wines. If the juice is colder than this, warm it by gentle heating, but do not boil as this
affects the flavour of the wine.
Racking the Wine
"Racking" means transferring the fermenting wine away from the sediment at the bottom of the
bucket. Use a clear plastic tube to siphon off the wine into a sterilised fermentation jug. Do not
disturb the sediment at the base of the bucket – it is important to have a clear wine without
cloudiness or debris. Seal the top of the fermentation jug with a sterilised bung and a
fermentation airlock. Leave to ferment until no more carbon dioxide gas can be seen escaping
via the air lock (this means that all the available sugar has been converted into alcohol, or the
yeast has died and the fermentation is complete).
Bottling the Batch
After fermentation, the wine is bottled by siphoning it off into clean, sterilised bottles. Do not
fill the bottles to the top (leave about 5cm of head space) to allow room for fermentation in the
bottle if it happens. Insert a cork into the bottle using a hand corking machine.
Some wines can be drunk immediately, however most develop distinctive flavours and aromas by
leaving them to age for a while. The bottles should be laid on their sides during ageing to keep
the cork wet. If the cork dries out, it may allow air into the wine, which causes it to oxidise and
spoil.
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