The decline is partly due to a wet spring and a cool growing season which resulted in lower yields in many areas. The California Wine Institute said the conditions created a “balancing act, with some winegrowers trimming fruit or pulling leaves to assure full fruit maturity”.
It added: “The good news is that what was brought in displays remarkable quality throughout the state with several vintners predicting a more restrained, elegant style of wine.”
The crop is forecast as 3.3 million tons.
Michael Weis, winemaker at Groth Vineyards & Winery in the Napa Valley, said: “This year we went from winter directly to fall with very little time for normal summer vineyard activities.
“2010 was a cool year with several heat spikes that not only helped accelerate the maturation of slowly ripening clusters but also desiccated un-shaded fruit.
“It was a year for a great deal of work in the vineyard before, during and after veraison to be sure that only the best fruit reached the crush pad. The level of raisining in the Bordeaux varieties required extensive thinning just prior to picking. Fortunately, most fruit in our area had been picked before the big rain event in late October.”