Of all factors affecting the quality of a wine, the quality of the grapes more than any other factor determines the quality of the wine. Their quality is not only affected by their variety, but also by the weather during the growing season, the soil, the time of harvest, and the way they are pruned. The combination of these effects is often referred to as their terroir. The most common genus of wine grape is Vitis vinifera, which includes nearly all varieties of European origin.
The grapes are usually harvested from the vineyard in the fall, in the northern hemisphere from the middle of October until the beginning of November, or the middle of February until the beginning of March in the southern hemisphere.