Two words are expected to define this year's grape harvest: Late and light.
The harvest is expected to start several weeks later than normal, perhaps kicking off in late August due to cool spring weather that stalled the growing season.
Then, once farmers do start harvesting, most expect a light crop due to a burst of unseasonable rain in June that interfered with vine fertilization and resulted in inconsistent grape growth.
"It's going to be as small as we've seen in many, many years," said Bob Iantosca, director of winemaking at Gloria Ferrer in Sonoma. "We had a cool spring and a lot of shatter."
Iantosca is referring to a rare phenomenon that growers call "shatter," which occurs when rain interrupts the climax of a vine's reproductive cycle.
Normally, a grapevine self-fertilizes by dripping pollen from its stamen down onto its eggs — a process that results in the formation of grape bunches.
But this June, when many vines had started to drop millions of pollen seeds down onto their eggs, heavy rains roared down from Alaska. The unseasonable rain washed away pollen and in some cases prevented a little cap on the stamen from popping off — in effect creating a natural prophylactic that stymied all those reproductive cells from reaching the vine's eggs.
"Now this season is a big question mark," said Chris Bowen, vineyard manager at Hunter Farms, usually one of the first to harvest grapes in Sonoma County. "I'm going to be at least 25 percent down in pinot noir."
Iantosca said this year's crop "could be historically low, aside from the severe frost years" such as 2008, when freezing weather in late spring destroyed a large swath of the year's crop.
Many growers are trying to determine just how small their crops will be.