Search for wine ‘smoke taint' solutions intensifies after Northern California wildfires

The international pursuit of ways to predict how much smoke from a wildfire will end up in finished wine and what to do about it got a boost when the dark clouds of particles pumped out by the massive North Bay fires in October descended on the University of California, Davis, experimental vineyard in Napa Valley.

'The moment the smoke started, my phone started ringing off the hook,' said Anita Olberholster, Ph.D., a specialist in the science of winemaking for University of California Cooperative Extension. When the fires erupted Oct. 8, most of the North Coast winegrape crop had been picked, but some late-ripening fruit, particularly cabernet sauvignon was still on the vine, in the home stretch of the 2017 harvest. 'It quickly realized how thin the data is I need to base recommendations on.'

Australian researchers had done extensive studies of a number of years on the interplay between smoke in the air and unpleasant 'ashtray' smells and flavors in the bottle, and such work continues Down Under. Knowledge has increased about the number of culprit compounds to test for — now seven, up from two — but how tests on grapes and on wine over time will predict 'smoke taint' and how that relates to winery fixes remains to be solved, Olberholster said.

As the Business Journal reported in November as samples of possibly tainted wine were flooding into commercial wine labs, a big challenge in such testing is the chemical markers associated with the off odors and flavors travel come in two forms: nonvolatile precursors and volatile compounds consumers can detect. The nonvolatiles bond to sugars in the grape juice and get released gradually during fermentation into the volatile, or free, form.

Commercial labs have precision in detecting levels of the nonvolatile and volatile chemicals, but the meaning of those levels in predicting taint isn't well-known, Olberholster said. And insurance companies have been using varying levels in determining claims for crop insurance.

'The best they get is 70 percent probability for volatiles,' she said about the lab results.

Trouble is, different varieties of grapes — such as syrah — have naturally high levels of the precursors, she said. And any time a wine spends in contact with toasted oak will skew the numbers.

Olberholster is working with grape and wine chemistry researcher Tom Collins of Washington State University to study the process of the release of the problematic volatile compounds and the testing methods that can better predict results. At the same time, Elizabeth Tomasino, assistant professor of enology at Oregon State University, is seeking grant money for a large, multiyear study on this.

'Unfortunately, I don't think fire events will decrease,' Olberholster said. 'This may possibly happen again, and we need to be ready to help the industry again.'

The fires near the UC Davis vineyard provided the perfect experimental platform, so she and her research team sprang into action to start their own research project on the fly. Remaining grapes on those vines were picked, loads of commercially grown grapes deemed too questionable to accept at a winery were accepted. Off the test vines came 6 tons of grapes, and the research winery at the Davis campus took in two loads from growers, resulting in 10 tons to test from four locations in the North Coast.

Different from a commercial winery, where up to tons at a time are prepared for fermentation, the research winery's fermenter only accepts 300 pounds at a time. Samples are taken in triplicate at multiple stages of the grape's travel from bin to bottle.

'The wines need to be very close to each other, so we can trust the treatments we test,' Olberholter said.

It's been five months since the suspect grapes stared becoming wine at the Davis research facility. They made larger-scale wines with a variety of yeasts known for imparting variable fruitiness, wines that had a spectrum of contact with oak and wood alternatives, wine at different temperatures and length of contact with the grape skins.

'Maybe lower fermentation temperatures or less contact time will make an impact,' Olberholster said. 'If it extracts in 10 minutes, it's not worth recommending. But if it's over a few days, there might be a change in winemaking style to get less of the compounds.'

Bottled test wines were tasted recently, but measurements on those samples aren't yet available, she said.

'They all have different levels of smoky character,' Olberholter said. 'Some on the nose are actually quite pleasant and not smoky, but the aftertaste is the problem. All of them, even if in small amounts, had that 'old smoke,' 'ashtray,' 'new smoke' aftertaste. It all depends on how sensitive you're going to be at it.'

A good thing about when the smoky compounds are in their free form is there are treatment methods that have found to be effective before bottling, Olberholster said. One is reverse-osmosis filtration, which can impact wine color. Another the Australian researchers found to be effective and are reinvestigating are about a dozen different activated-charcoal fining agents, but the optimal type and amount is key to avoid stripping wine of its character.

'We want to find something that will remove the smoky compounds but as little as possible of anything else,' Olberholster said.

Jeff Quackenbush (jquackenbush@busjrnl.com, 707-521-4256) covers the wine business and commercial construction and real estate.