Jon Phillips, a Santa Rosa winemaker, walked into his local hardware store in search of a generator only to learn another customer had walked out with the last one.

“I missed it by minutes,” said Phillips, who owns Inspiration Vineyards and Winery.

For months he’s debated investing in a generator, but there was a fresh urgency Monday: PG&E warned of a planned power outage that could have affected 124,000 customers, part of a preemptive measure to lessen the risk of wildfires. PG&E ended up calling off the shut-off in Sonoma, Napa and Lake counties, but the threat remains, with outages still possible Tuesday and Wednesday.

PG&E intentionally turned off electric lines because of fire danger for the first time last year under a program the company developed after its equipment started many wildfires that burned through Wine Country in October 2017. After the deadly Camp Fire, which was linked to a PG&E transmission line, the utility greatly expanded the scope of power shut-offs, which could now affect any of its millions of customers in Northern California.

At Phillips’ facility on Coffey Lane, he makes his own label and counts 12 small-batch winemakers as clients. While the business park has a backup generator that’s enough to keep the lights on, Inspiration Vineyards doesn’t have its own backup power. He ended up ordering one online for $1,200 that will be delivered next week.

Even though Monday’s power shut-offs were canceled for the North Bay, the panic around them exposed how ill-prepared many wineries are. Many wineries can’t afford expensive generators — but they can hardly afford a loss of power, either. Their owners are now reckoning with the possibility that power outages could become a regular feature of harvest season.

California’s wildfire season happens to overlap with the grape harvest, the time of year in which wineries most acutely depend on electricity. After wine grapes are picked, they are processed through various types of machinery — destemmers, sorting tables, crushers, pumps — none of which can work without electrical power. “If we learned we were getting our power shut down, we’d have to cancel our picks,” said Mick Unti, owner of Unti Vineyards in Healdsburg.

Grape picking can be postponed. But a greater concern for winemakers is the loss of temperature control in their cellars. Wine needs to be stored in a cool environment at every stage of its development, from barrel to bottle, ideally between 50 and 60 degrees. If exposed to excessive heat, it can be ruined.

The need for a cool environment is especially urgent while wines are fermenting, as they are during harvest season. Fermentations are extremely temperature-sensitive, and most wineries use specialized cooling systems. Without those, winemakers have to resort to other measures. Unti had dry ice delivered to his winery on Monday, for example.

And the cellar isn’t the only part of a winery that a power loss would affect. “Besides all the craziness of harvest, this is our busiest time of year with consumers coming into the tasting room as well,” said Jake Bilbro, owner of Healdsburg’s Limerick Lane Cellars. “It would not be great if I could not run credit cards.”

After losing power for nine days during 2017’s October wildfires, Bouchaine Vineyards in Napa decided to rent a generator for this harvest season. “We were worried if we didn’t get one in August there wouldn’t be one available in September,” said Bouchaine winemaker Chris Kajani. In addition to making Bouchaine’s own wine, Kajani is also processing 200 tons of grapes for a custom-crush client this fall, and felt she couldn’t let the client down in the case of a power loss.

“We didn’t have the electrical setup for it,” Kajani said of the generator. It took a few weeks to get it set up. She’s crossing her fingers that it will work if they need to use it, “but we haven’t tried turning it on yet,” she said. “This is all uncharted territory.”

To add to the complicated process, large generators need air permits to operate, according to the Bay Area Air Quality Management District.

“Anything that is over 50 horsepower or 30 kilowatts needs an air permit, which can take weeks to get,” said Liesl Ramsay, owner of Leete Generators in Santa Rosa.

Other small wineries said they couldn’t afford to rent or buy a generator — and that even if they could, it’s now too late. “I’m not of a size, nor do I have a flexible budget to go buy a massive diesel generator,” said Bilbro. “And even if I did, it’s not like I would have just gone and bought a generator just to have it sit there, just in case we needed it.”

Ramsay, who lost her home in the 2017 Tubbs Fire, said visits to her store and calls about emergency generators spike whenever PG&E gives a warning for power shut-offs. “Our sales increase by almost 200% whenever the shut-offs are announced.” She said wineries were a focus right now: “They’re in the middle of crush season with millions at stake.”

Her store specializes in industrial, custom generators that can take weeks to build. A trailer-mounted 100-kilowatt generator sells for as much as $40,000. Even smaller systems can cost between $6,000 and $14,000.

She said she’s come across customers thinking they can plug a generator into a wall.

“They can’t —your electrical grid has to be set up to take in a generator,” she said. “If someone were to come into my store today, they’d be out of luck.”

Will PG&E’s planned outages become a fact of life for California wineries, another precarious factor to plan for during harvest every year? If so, the outages may leave winemakers with an especially thorny problem. The outages are likely to occur during hot, dry periods, exactly the sort of conditions that would accelerate grapes’ ripening and potentially result in overripe fruit. The hottest moments of harvest are the moments when winemakers need the most flexibility in deciding when to pick grapes.

Under the best conditions, “it’s already challenging to figure out when to pick,” said Unti. “It’s another complication to think that the forecast is for three days of 98-degree weather next week, and are we going to be in a position where we can’t even process fruit? That really messes us up.”

“This is going to be something that we’re going to have to deal with in the future, from now on,” Unti continued. “As wineries, we’re always dealing with some things that are out of our control — the weather. Now we have this other variable?”

Shwanika Narayan and Esther Mobley are San Francisco Chronicle staff writers. Email: shwanika.narayan@sfchronicle.com, emobley@sfchronicle.com Twitter: @shwanika, @Esther_mobley