Vineyards - Napa California
Napa Valley, San Francisco North Bay, Ca. USA

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.

Harvest is the picking of the grapes and in many ways the first step in wine production. Grapes are either harvested mechanically or by hand. The decision to harvest grapes is typically made by the winemaker and informed by the level of sugar (called °Brix), acid (TA or Titratable Acidity as expressed by tartaric acid equivalents) and pH of the grapes, as well as berry flavor, tannin development and overall disposition of the grapevine and weather forecasts. °Brix is a measure of the soluble solids in the grape juice and represents not only the sugars but also acids and to a lesser degree esters, terpenes and tannins. The level of sugar in the grapes is important not only because it will determine the final alcohol content of the wine, but also because it is an indirect index of grape maturity.

Mechanical harvesters are large tractors that straddle grapevine trellises and, using firm plastic or rubber rods, strike the fruiting zone of the grapevine to dislodge the grapes from the rachis. Mechanical harvestors have the advantage of being able to cover a large area of vineyard land in a relatively short period of time, and with a minimum investment of manpower per harvested ton. A disadvantage of mechanical harvesting is the indiscriminate inclusion of foreign non-grape material in the gondola by the action of the harvestor. Depending on the trellis system and grapevine canopy management, this foreign material can be moldy grapes, leaves, canes, metal debris, rocks and even small animals.