The 2017 vintage may be a tough one for many Napa and Sonoma winemakers after last week's heatwave, which hit right before harvest for red varietals like Cabernet. The harvest had been shaping up to be a good one, as the Chronicle initially reported just as the heatwave struck, but then came three consecutive days of 110-degree temperatures in St. Helena, and a generally sweltering weekend all over wine country, and winemakers are left assessing the damage.

As the Chronicle reports now, "raisining" is happening all over vineyards up north, given to the fact that some grape varietals couldn't be harvested in time. Lots of the whites for 2017 should be fine, since they get harvested earlier, mostly in August. And some Pinot Noir producers were able to rush out and harvest ahead of the heatwave. But for other who needed the extra couple weeks in September to achieve ripeness, they're stuck with half-dried clusters of grapes that literally cooked in last week's sun.

"I’ve been making wine for 34 years, and I don’t think Napa’s ever seen this excessive heat at this stage of ripeness,” says Pam Starr of Crocker & Starr Wines in St. Helena, speaking to the Chronicle.

Hirsch winemaker Anthony Filiberti says that about 20 percent of his grapes are done-for, either due to water evaporation or raisining.

The other problem has come from a labor shortage among migrant grape harvesters, and when suddenly everyone want to rush to harvest at once, that creates a greater shortage — the workers can't be everywhere at once.

Now winemakers are left to sort the grapes as they harvest them, separate out the raisins, and hope that this year's wines don't all taste like jam.