Although we usually think of the fruit that grows on vines as grapes, and this is what they are usually called, in wine-making terms, this individual grape is often referred to as a berry.
This berry is formed of the berry skin (epidermis), the berry pulp, or flesh, (the part of the berry containing the juice) and seeds.
The layer just under the skin is called the peripheral pulp. This is where most of the coloured pigments, tannins and flavour constituents can be found.
In order to make red wine, the juice of the black grapes is fermented with the skins in order to extract flavour, tannins and colour.
If you want to make a white wine, or indeed a sparkling wine such as Champagne, from black grapes, then the juice has to be separated from the skins before fermentation. The juice itself is clear.
The seeds contain a high level of tannins and can make a wine bitter if too much of these are released during pressing.