1 What is Wine? Wine is fermented grape juice. The grapes are crushed to release their sweet juice. Alcoholic fermentation is needed to change the grape juice into wine.
Parts of a Grape There are two principal types of grapes: white grapes and black grapes. On the inside, these grapes look very similar. The key difference between them is that black grapes have deeply coloured skins that also contain tannins.
Grape Skins
Pulp
This is a black grape, which has a deeply coloured skin.
The pulp of a grape is soft and fleshy. The colour of the pulp is the same regardless of the colour of the grape skins.
The skin also contains tannins, which can make your mouth feel dry.
The pulp contains the grape juice, which is mostly made up of water, sugar and acid.
The skin of white grapes has a golden colour.
Alcoholic Fermentation In order for alcoholic fermentation to take place, yeast are required. Yeast are microscopic organisms that eat sugar and convert it into alcohol and carbon dioxide gas. In most cases this process continues until the yeast have eaten all of the sugar (but see also section Sweetness on p. 10). The alcohol stays in the newly made wine and in most cases the carbon dioxide escapes into the atmosphere. sugar
+
yeast
alcoholic fermentation
alcohol
+
carbon dioxide
The level of alcohol within a wine is usually measured as ‘alcohol by volume’ (abv); in other words, 10% abv means that ten per cent of the liquid is alcohol.
