Fruit production of grapes is highly dependent on the goals of the grape grower. If the goal is wine production, then a balance must be made between productivity and fruit quality. If the goal is fresh table grapes then usually more grapes can be left on the vine. However, berry size will be reduced at higher yield levels. Winegrape vines can produce from 1 to 12+ tons per acre when mature, with the optimal range being between 3 to 5 tons per acre. Table grapes may be much higher at 8 to 10 tons per acre. At bunch closure (the best time to thin) when cluster thinning
follow these guidelines: if a shoot is less than 12 inches long, remove all clusters from that shoot; if a shoot is 12 to 24 inches long, leave one cluster on that shoot; and if the cluster is up to 36 inches long, leave two clusters on that shoot. You may wish to further reduce yield on the longer shoots. However, removing an excessive proportion of fruit will further stimulate shoot growth.