Quick, tiny ferments could help smoky-wary California North Coast wineries opt to harvest or not

It’s been a year since the first of two massive wildfires started throwing the 2020 North Coast wine grape harvest into turmoil. And as the first 2021 grapes are coming into local wineries, the region’s go-to expert on smoke’s impact on wine reveals the tough lessons learned.

Some of the big research questions like how many of key test indicators for smoke damage in grapes and wine are already present at significant levels in certain varieties may take a few more years for solid answers to be developed. But UC Davis’s Anita Oberholster and colleagues at Pacific Northwest institutions have pulled enough research from around the world and their own work during nearly annual West Coast conflagrations to develop tactics vineyard and winery teams can deploy this season.

One battle that the industry is waging is against public misconceptions, she said.

“Just because there’s lot of smoke everywhere and just because the air smells like smoke around a vineyard you see does not mean that it’s impacted. It’s not that simple,” said Oberholster, Ph.D., associate cooperative extension specialist in enology at the Solano-Yolo institution.

For one thing, research has found that how old the smoke is generally makes a big difference on how much impact it may have on grapes, she said.

“What we’re really concerned about is this really fresh smoke, because the volatile phenols in the air photo-oxidize and break down pretty quickly,” Oberholster said.

That makes it possible for a vineyard next to a fire to get less or negligible smoke impact if wind direction, terrain and other factors delay the arrival of the smoke, she said.

Smoke damage or “taint” in grapes and wine made with them are connected with several chemical compounds released during ignition of fuels. When coming from specially toasted oak barrels, these volatile phenols can be part of a desired wine style. But in heavy levels, these easily sniffed-out compounds can leave the wine with an overpowering aroma described as smoky, medicinal, chemical, burnt or ashtray-like.

What complicates the detection of smoke damage further is that these volatile phenols easily bind with sugars in the grapes and juice. Testing for just the unbound, or “free,” compounds won’t reveal what will be detectible after fermentation releases around 35% more of these smoke markers into the wine months after harvest, Oberholster said.

And when there are massive fires in many major wine regions along the West Coast, as happened last year, tests on grapes and juice can get backed up for weeks. That deprives growers and vintners of information for whether to harvest fruit or not, particularly since grape purchase contracts in the past few years have included general to specific language about what constitutes smoke damage.

Oberholster and fellow smoke-damage researchers such as Tom Collins of Washington State University have become champions of a ultra-small-scale fermentations as a tool used by Australian vintners for several years to better gauge what the true level of free smoke compounds will be after juice transforms to wine.

Measured in a few kilograms versus the typical tons for common wine tanks, these bucket fermentations, accelerated with nitrogen, look to get a quick take on the likelihood of grapes from a specific vineyard block or part thereof having smoke problems after harvest.

“Growers and wineries can taste how grapes will evolve and taste,” Oberholster said. “There’s still risk, because smoke can show up months later for low-impacted wines. For highly impacted wines, it shows up right away.”

And these bucket fermentations also have been helpful with crop insurance claims, particularly when the buckets are tracked to specific parts of the vineyard to show how much of the crop was damaged, Oberholster said.

But one of the problems with bucket fermentations and other sensory testing for smoke is that 20%-22% of people can’t detect it, she said.

“That’s a problem if the winemaker is not sensitive to smoke,” Oberholster said.

So last year she made calibration wines and a tasting protocol to use with screening those who will test for smoke and to ensure reliability. She found that because of the persistence of the smoke compounds on the palate, tasters need to rinse their mouths with water and wait 2 minutes for saliva to replenish before trying the next sample. The tasters also should have a sample of what a wine normally tastes like.

But while smoke ages quickly in the air, ash can be a vehicle to protect the smoky phenols longer, Oberholster said, pointing to Collins’s recent research into a few grape varieties on whether the age of age on the grapes makes a difference. Wet ash tends to release more of these problematic phenols than dry ash, and ash that’s fallen in the past 24 hours may release more than what’s a week old.

But Oberholster found less conclusive connections between whether leaves that have been in contact with ash can transfer the compounds to the grapes if they come with the fruit to the winery crushpad.

One of the longer-term research goals is to build thresholds for these smoky volatile phenols that can be use by grape variety, region, style and other parameters to create testing benchmarks that could add more specificity to grape-purchase contracts. For example, a wine with vegetative notes can amplify the perception of smoke, as can full-bodied red wines more than medium-bodied ones.

“We’re hoping that this year most of the wine regions will not be impacted by smoke, so we can go back to all the sites that were impacted and get site-specific data. We want bookends of what is normal and what is impacted,” Oberholster said.

She is working with Collins and Elizabeth Tomasino of the Oregon Wine Research Institute on a grant to fill out these thresholds.

Jeff Quackenbush covers wine, construction and real estate. Before the Business Journal, he wrote for Bay City News Service in San Francisco. He has a degree from Walla Walla University. Reach him at jquackenbush@busjrnl.com or 707-521-4256.