A small percentage of the 2017 North Coast winegrape crop was still on the vines when wildfires raged in Sonoma, Napa, Mendocino, Lake and Solano counties early last month.
But laboratories in the region have been busy undertaking the tricky task of gauging how much, if any, of the smoke that filled the air for days made it into the remaining grapes, and winemakers are weighing what to do with the results.
More than 90 percent of the grapes in Napa and Sonoma county had been harvested by the time the fires erupted Oct. 8–9. The remainder was later-ripening varieties such as Napa Valley’s prized cabernet sauvignon, and about three-quarters of that already had been brought in. Smoke significantly reduced air quality for more than a week and a half downwind of the flames.
The fires killed 43, destroyed thousands of homes and buildings, including 15 wineries, and scorched more than 100,000 acres before being totally contained Oct. 31.
But one of the immediate questions in Wine Country has been what impact will the smoke have on the world-class wine the region is known for. Science on “smoke taint,” or noticeable smoky aromas and flavors in wine, has been evolving for a decade and a half, led by researchers in Australia, where wildfires near winegrowing areas are frequent. Out of that work plus experience from the North Coast after the Mendocino County fires of 2008 have come tests that can be done on grapes in the vineyard, juice at the crushpad and wine in the vintner’s cellar.
“Since the fires, we’re going 24/7,” said José Santos, president of Enartis’s Windsor-based Vinquiry laboratory, which has branches in St. Helena and on the Central and South California Coast.
In the first days of the North Coast fires, his labs were receiving more than 200 samples a day. The recommended sample size is five to seven vine branches or, better, 200–300 grape berries, taken from representative areas of a block or whole vineyard. Because the samples each take 30–40 minutes for the equipment to analyze, the staff has been going as far as setting them for analysis overnight, getting results in the morning.
Adding to the backlog are samples that have been pouring in from winegrowing regions in Oregon, Washington and British Columbia, Santos said.
WAIT AND SEE
Wineries have been sending in grape samples from suspect vineyards. Some have rejected deliveries of fruit with results that suggest a problem. That’s because the problem components of smoke concentrate in the skins. Other vintners have taken a wait-and-see approach because of the complexity of connecting test results with unwanted smokiness in finished wine.
“The degree of taint, if any, is still being determined, as the juice results usually tend to trend lower than those past fermentation,” said Randy Ullom, winemaster for Kendall-Jackson.
That’s because the process of fermentation unlocks the chemical compounds associated with the smells and tastes of burned wood, such as “smoky,” “burnt,” “bacon,” “medicinal” or “ash.” That’s because the enzymatic action of the yeasts during fermentation and hydrolysis from the wine’s acids unbind these phenolic compounds from sugars in the juice, according to Santos.
Depending on a given wine’s acidity, complexity and other factors, wine made from grapes or juice with low proportions of indicator freed volatile phenols in the grapes or juice may have higher proportions of the freed form — detectable to the palate and nose — after alcoholic fermentation in several months, he said.