The Science of Removing Smoke Taint

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Smoke taint in wine first became commonly encountered in Australia in the late 1990s. Since then, it has become an occasional, but challenging, problem for winemakers in many regions, including the Western U.S. Recent large-scale events in the North Coast like the Kincade and Tubbs/Nuns fires were preceded by a large (but not as destructive) event in 2008 (Mendocino) and smaller fires in the early 2000s from Canada’s Okanagan Valley to Mt. Veeder. Over that time, only a few processes have been developed that enable wineries to remove the resulting flavors and aromas in order to make consistently high-quality wine.

When vines are actively developing their berries, they translocate what they breathe into the berries, along with sugar and other flavor compounds. When the grapes are then crushed and turned into wine, it includes trace amounts of compounds that taste smoky, smell ashy, and leave a harsh finish after the wine is swallowed. These smoke-related flavors are distinctly different from the smoky characteristics sometimes derived from toasted oak, evoking more of an ashtray flavor instead of a cigar-box essence.

Obviously these are undesirable characteristics, so winemakers have experimented with various ways to remove them from wine. Fining (typically with carbon or isinglass) does reduce them, but not nearly as fast as it reduces desirable flavors and aromas. Short skin contact also will reduce smokiness, but, again, the negative effects of the short ferment diminish the quality of the wine much more than the smoke taint. Likewise, early picking simply results in poor quality, and nominal mitigation of the smoke characteristics.

Crossflow filtration, however, is one process that has a small beneficial effect due to removal of colloids, weakly held-together microscopic substances that bind some precursors and free compounds causing smoke related flavors and aromas. It isn’t enough on it’s own, but, unlike some of the above methods, it doesn’t negatively affect quality. “When our mobile crossflow systems filter smoke affected wines, the client may be pleasantly surprised to see the improved flavor and aroma, along with the expected clarity and stability,” said ATP Group’s Isaac Sendejas, Project Coordinator.

A 2005 Australian study demonstrated that existing membrane methods for smoke removal were initially effective. However, sometimes smoke-taint compounds bound to sugar (glycosides) are slowly released back into wine, resulting in scant smoke flavors and aromas in the future. Some researchers have tried to break down these sugar-smoke complexes with enzymes, but lab results demonstrate that this fails to release these bound flavors and aromas. As a result, it has become standard operating procedure to leave no residual sugar in wine made from smoke-exposed grapes.

In response to these confounding issues, we at Mavrik North America developed new membrane and adsorption regimens to efficiently remove the full spectrum of flavors and aromas. It’s a good idea to remove more than is necessary to drop below the sensory threshold. The key we found is to isolate the offensive elements and then adsorb (only the offensive elements) quickly and completely. This protects the integrity of the wine, while limiting the processing.

There are a couple of factors that can present challenges in finishing the wine. For example, even very low (and very normal) levels of some common microbes (such as Brettanomyces and Dekkera) can elevate the aromatic and flavor profile of trace smoke levels. Likewise, blending—even two wines not showing smoke flavors—can sometimes result in smoke flavors and aromas. For these reasons, we recommend treating wine not long before bottling and blending carefully.

A variety of products from oak to tannin extracts have been used in trials. However, none of them will sufficiently cover up more than a trace amount of smoke. But their use after the removal of the smoke taint flavors and compounds are a great way for a winemaker to fine tune the wine that has, until that point, been hiding behind a cloak of smoke.

Once a wine is treated, it can be bottled and sold. If done carefully, it will show no negative effects, or smoke character. In recent years, some large wineries have rejected grapes because they show smoke taint on analysis. With a comprehensive strategy for removing smoke taint, making wine from those grapes is possible, albeit with a slightly higher production cost.

 

Robert Kreisher, Ph.D. first encountered smoke tainted wine grapes in Australia in the early 2000s. Since then, he has developed a gentle process for removing the smoke taint used by Mavrik North America to complement their existing processes for gently removing volatile acidity, alcohol, and much more in order to help winemakers perfect their wines. For more information, visit www.mavrikna.com, or call (707) 320-0672.

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