Raasch declined to identify the affected wineries, saying the investigation is ongoing. Deputies in the area have been advised of the crimes, he said, and are trying to be more visible in the rural winemaking region.

Raasch said the burglars seem sophisticated and determined. They know how to find isolated tasting rooms and locate the materials they want. In one case, the burglars spotted a surveillance camera and skirted it, leaving police with little visual evidence of what happened.

"We think it is probably someone who's worked at a winery before," he said, though investigators have not yet identified any suspects.

And the burglars are fast. In at least one case, he said, an alarm was tripped, but the thieves were gone by the time deputies arrived.

While it is not uncommon for equipment or metal fixtures to be taken from outside of vineyards and wineries, Raasch and winery owners say this is the first time they can recall anyone breaking into the tasting rooms in Sonoma County.

"It may make people more aware, more diligent about locking up, filing things away, keeping things confidential," said David Mounts, owner of Mounts Family Winery and a board member of the Winegrowers of Dry Creek Valley.

The thefts seem to require considerable effort, Mounts said, since many tasting rooms have heavy doors and locks, and many are gated.

"Obviously, they are pretty intelligent burglars, not just random hits to get wine," he said.

Mounts' group sent an alert to all 210 members, including 62 wineries, Office Manager Debbie Colgrove said.

"We just want our people to be alert and aware of it," she said.

Napa Valley experienced a similar rash of thefts some years ago, Napa County Sheriff's Capt. Tracey Stuart said, but there have been no recent reports of trouble. The county has a bigger problem with thieves, at least some coming up from the lower Bay Area, stealing outdoor fixtures or breaking into mailboxes at wineries and other rural locations.

"A lot of our patrol is in those remote areas," she said. "Our deputies are just out there trying to be seen" to deter would-be thieves.