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North Coast winemakers clear the air on ‘smoke taint’

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.

“The analysis we offer is critical, because it helps winemakers assess how much potential smoke taint is possible in grapes, juice or wine,” Santos said. “You can think of the total pool of smoke taint aromas as an iceberg. The detectable aromatic fraction before or just after fermentation is oftentimes just the tip of the iceberg. A nonvolatile, bound fraction exists in the wine, which over time will release smoke taint aromas during aging.”

The rate at which smoke taint aromas appear in a wine is often dependent on that wines acidity, temperature of aging and phenolics.

“It can be several months before a wine starts to show ashy, smoky characters, so the analysis prepares the winemaker for this situation,” Santos said.

Chief among the eight culprit compounds for “smoke taint” are guaiacol, 4-methylguaiacol, o-cresol, p-cresol and m-cresol. The two key taint indicators labs focus on are the first two.

“Our recommendation is if some grapes are fairly high for our reference numbers, we take slightly different (winemaking) process for these,” Santos said. “For those with (smoke taint) markers but lower numbers, we recommend go in process normal way. We learned from the 2008 fires that we treat the wine now and six months later return and assess levels on a case-by-case situation.”

Establishing a baseline of how much bound and unbound guaiacol and 4-methylguaiacol is present is especially important for red wines that will be aged in barrels a fair amount of time — two or more years for fine wines — allowing hydrolysis to free the smoky phenols, Santos said. These baselines can point to what corrections might be needed later.

‘WHAT IS SMOKE TAINT ANYWAY?’

Among the challenges with measuring the smoke-taint indicators and doing sensory tests on the wine is determining what how much smoke in wine is too much, according to Clark Smith, a winemaker and production consultant with WineSmith in Santa Rosa. He developed methods for reverse-osmosis filtration and other wine-processing techniques over the past few decades.

“Consider that the wine industry spends billions of dollars trying to get fire smells and flavors into the wine,” Smith said. “So, what is smoke taint anyway? We’re really not sure.”

Oak has been a part of winemaking for centuries, and science has revealed in recent decades how the chemical characteristics of the wood helps develop certain aspects of wines. And the art of cooperage has brought refinements to winemaking via fire and heat treatments to the wood in the barrels, and in stainless-steel and other vessels via toasted chips or arrays of staves.

That’s why wine that is trending higher in smoky volatile phenolics may be better-served with less time touching toasted oak, Santos said.

“What we suggest is to rethink the oak program in order to integrate any smoke taint,” he said. “This can be done with using oak barrels, chips or tannins with different levels of toast, modulating the aroma profile and integrating the smoke compounds. We are currently testing new winemaking treating materials to remove smoke taint, such as chitosan, chitin glucan and yeast-derived products.”

Similar recommendations from Santos and other researchers are to watch for winemaking techniques that maximize extraction of pigment and tannin from the skins, such as pulling juice from second-pressings of grapes.

Research on other food products has shown that smoky compounds also are key to what draws people to coffee, bacon, smoked meats, toasted almonds and bourbon, Smith said. For example, caramelization of coffee beans gives butterscotch aromas, while thiols give a bit of skunkiness associated with some fine blends. And the Maillard reaction on proteins in the beans leads to bacon and tawny fruit notes.

“Guaiacol and cresol also present in things we love,” he said. “Everyone has their own threshold between controlled and uncontrolled fire. It may be that smoke taint is the absence of vanilla and there’s nothing sexy and sweet. It may be about getting the balance back.”

TREATING FOR SMOKE

“There are many ways to reduce taint, and be sure there will not be any wines entering the market fully tainted,” said Randy Ullom, winemaster for Kendall-Jackson. “There are different methods of fermentation that are used by most wineries in these rare instances, such as less skin-contact time, quicker ferments, sometimes, even flashing can help.”

Flash détente (French for “relaxation”) is a process developed in Europe and popularized in the U.S. in the past decade. The process heats grapes to 175–185 degrees Fahrenheit then pumping the fruit into a vacuum chamber, which evaporates — “flashes” — the water in the must into steam and explosively releasing color and tannin in the skins. It’s an alternative to traditional maceration of the must in fermentation tanks and used to treat challenges such as unripe and mold flavors.

“Also, postfermentation, special, focused filtration can be used that help eliminate any taint, if needed, down to the molecular level,” Ullom said.

Enzymes are used to convert the bound smoky phenols into the free form, then employ reverse-osmosis filtration to remove those compounds. Because this can also lead to removal of some pigment, Santos is recommending his clients that are playing the long game focus on stabilizing the rich, deep color they seek before bottling, because reverse-osmosis filtration can remove a small percentage of the color in the process.

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