A grape is made up of several different parts. Most of the grape is made of water, and this water eventually ends up in the wine. In fact, in ancient times, wine was an excellent source of clean water, which added to its popularity. Grapes also contain sugar, pips (seeds), skin, and pulp. All of these parts are important when it comes to making wine:
- Sugar's role in winemaking comes into play during fermentation, because yeast processes sugar into alcohol. The amount of sugar in the grapes is very important, as an indicator of ripeness. There are several different scales used to measure ripeness in vineyards, depending on the vineyards location in the world. In France, they use the Baumé scale, in Germany, Oechsle or KMW, or Brix in California. All of these scales measure the must weight, or the density of the juice inside the grape. All of these scales provide an approximate judge of how high the alcohol content of wine will be from a given grape. As the harvesting season approaches, workers will comb the vineyard testing grapes on one of these scales, and the winemaker will use this information to decide when to harvest.
- The pulp in almost all grapes, including black grapes, is colorless. You might think that black grapes have a dark pulp and excrete dark juice, but in fact all grapes juice looks like clear grape juice.
- The color of red wine instead comes from the dark skins, that are soaked in the juice for a time during fermentation to provide that color as well as tannins.Grape skins also have natural yeasts living on them, which start the fermentation process once the grapes are crushed.
- The pips, or seeds, inside grapes contain tannins, but also a bitter astringent flavor that does not taste good in wine. For this reason, grapes must be crushed carefully, so the pips are not broken. With modern winemaking advances, this is rarely a problem today.