2008 - Smoke Taint Vintage?We are experiencing a high pressure ridge here on the West Coast just now that is 1) baking us under a blanket of heat, and 2) wreaking havoc with our air quality.
After a cool-to-balmy weekend it really started to heat up Monday, when I saw the mercury at 106° F in the afternoon. Yesterday it was 108° and we are expecting 110° today and tomorrow.
Also since Monday we have had blood-red sunrises and sunsets again, as we did in the middle of June. Smoke from every fire between Shasta and Santa Barbara is trapped under this statewide temperature inversion. Here in Sonoma we just have hazy skies. Closer to the fires the air is thick with smoke and the smell of burning.
The million dollar question (literally) for winemakers this vintage is, "will the smoke affect the grapes?".
The issue is current, showing up in posts on Wines & Vines ("Dark Cloud Over California Growers", July 1, 2008) and Wine Spectator ("Northern California Vineyards Impacted by Wildfires", July 9, 2008).
My interest in this question started last Wednesday when Alex MacGregor, a winemaker friend of mine in Ukiah, called to ask me if I had any experience with smoke tainted wines. I had not, but he mentioned that he had, when he was working at a winery in the Okanagan Valley in 2003.
That year a large forest fire filled the area with smoke, and actually burnt through the ground cover of the vineyard where my friend worked, affecting their Merlot. Tom DiBello, winemaker at Cedar Creek Winery in the Okanagan Valley (and a former colleague at Stag's Leap Wine Cellars back in the day) mentioned in a 2005 interview with Appellation America that the fire affected their Pinot Noir in 2003.
That very afternoon last week I recieved an email from Arthur Przebinda, author of "Wine Sooth", asking for my take on smoke taint wines. I had already started some online research when Arthur emailed me a short list of references to brushfires in Western Australia and Victoria in 2003-04 and 2006-07 which caused substantial commercial losses due to smoke taint in wines (1, 2). I have cited some of the references Arthur provided throughout this post (thanks for the heads-up, Arthur!).
I have spent the last week reviewing references and talking to various people. The problem is real. The Australian Wine Research Institute (AWRI) has a current page on smoke taint on their website, which cites a seven-page Industry Report on the problem. The Victoria Department of Primary Industries (VDPI) presents a more detailed (bandwidth-choking) 59-page report. Kennison et al. report on smoke-derived taint in wine in J Agric Food Chem. 2007 Dec 26;55(26):10897-901 (abstract here).
- Smoke actually gets into the berries not on the surface, dissolved in the waxy cuticle as I first presumed.
- Ash fall does not contribute to taint, and washing the clusters before harvest or before crushing will not reduce taint.
- The mode of entry appears to be transpiration through the leaves. It is presumed that the passive uptake of smoke-related compounds is blocked by the Casparian strip in the root structures.
- The critical period is during rapid berry expansion around veraison, when the vines are translocating most into the berries.
- The compounds that appear in tainted tissues, berries and wines are: guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-ethylphenol, eugenol, and furfural.
- These compounds don't appear to be metabolized once they are in the grapes small decreases in concentration after exposure are attributed to berry expansion.
- Some varietals are more susceptible than others: the VDPI report cites Sangiovese (most) > Cabernet Sauvignon > Chardonnay > Shiraz > Merlot (least); relative susceptibilities of other varietals were not mentioned.
- Taint characters survive fermentation and most fining agents are ineffective, though carbon (OUCH!) will take some 4-methylguaiacol out.
- Reverse osmosis treatment can be used to reduce taint in finished wines, just as it has been used to reduce the presence of similar compounds produced by Brettanomyces. Melbourne-based Memstar is already promoting their service on their website (if their warnings on the risk of taint seem a bit hyperbolic um, they are selling a service after all) and Winetech is sure to follow.
In support, Rémy Charest, in a March 19, 2008 post to his blog "The Wine Case", noted regarding a smoke-affected wine that "the smokiness was noticeable by comparison with the other cuvées. I'm not sure anybody would have rated it a defect otherwise, or even noticed it as an external factor."
The Australian references also note that the effects of smoke taint are most problematic in white varietals. Nevertheless, I feel it would be unwise to underestimate the potential for damage to red grapes.
As I noted in an earlier post, we are mowing and discing more than usual at our Annadel Estate vineyard to minimize the risk of fire actually getting onto the property.
So far we have not had the kind of sustained, heavy, oppressive smoke that has impacted the Santa Barbara and Mendocino regions. But I will be taking precautions. I may have the grapes tested for taint compounds before harvest, especially if we have some serious smoke between now and then. I will work with the pickers extra hard to minimize leaf material in the lugs. I probably won't be doing any ferments on stems if there is a chance of taint.
And I'm thinking about maybe spraying the vines with Surround WP. I spoke with Katie Madigan at St. Francis Winery, where they have been using this engineered Kaolin material to protect against sunburn and reduce transpiration. They have been very happy with the wines they have made with Surround-treated grapes. I wonder if this material might reduce the susceptibility of the vines to smoke.