The quality of the grapes determines the quality of the wine more than any other factor. Grape quality is affected by variety as well as weather during the growing season, soil minerals and acidity, time of harvest, and pruning method. The combination of these effects is often referred to as the grape’s terroir.

Grapes are usually harvested from the vineyard from early September until the beginning of November in the northern hemisphere, or the middle of February until the beginning of March in the southern hemisphere^.  In some cool areas in the southern hemisphere, for example Tasmania, Australia, harvest extends into the month of May.

The most common species of wine grape is Vitis vinifera, which includes nearly all varieties of European origin.

Source: Wikipedia