By April Ingram
Knowing if You Have Smoke Taint Sooner
In many prominent grape growing regions around the globe, a new season, fire season, seems to be arriving on an increasingly regular basis. Drought conditions, high temperature, and wicked winds are turning small grassfires or a discarded cigarette into raging, devastating firestorms. The immediate concern for growers is for the safety of people and property, and then later surveying the damage to equipment, orchards and vineyards. The losses in recent years from wildfires have been catastrophic.
Long after the fire has passed, the potential of smoke taint ruining an entire vintage is a real concern. Undesirable contamination of grapes from smoke can result in less than desirable sensory expressions in the wine – smoky, burnt or ashy. When smoke taint is possible, winemakers have only two options: throw out an entire vintage or make wine and hope for the best. Researchers would like to give them more options and are looking into questions regarding the amount of smoke and how long it had contact with the grapes before it effectively ruins the vintage, what can be done to salvage the grapes and possibly alleviate perceptible taint, and earlier, more efficient detection of smoke taint.
At the University of British Columbia Okanagan (UBCO) in Kelowna British Columbia, Canada, new research conducted by Dr. Wesley Zandberg and Ph.D. candidate Matt Noestheden has uncovered a way to assess and quantify the amount of smoke taint, helping winemakers know the good or bad news sooner.
Volatile phenols are aromatic compounds found in Vitis Vinifera berries. They represent the key molecules responsible for the olfactory defects in wine. These compounds can be developed within the grape or originate from external sources. Some volatile phenols impart desirable sensory attributes, such as when the wine is barrel aged. Alternatively, the exposure of the grape to smoke may cause the fermented wine to lack some of its varietal characteristics and have variations of a burnt aroma; some have even described it as “burnt meat” or “band-aid” flavor and smell.
The Okanagan Valley of British Columbia is a diverse area, home to hundreds of vineyards, and sadly, frequent forest fires. Adding insult to injury, thick smoke from fires in neighboring Alberta and Washington State can also settle into the area. In 2003, a fire destroyed hundreds of homes in Kelowna and thousands of people evacuated. Due to the smoke and ash caused by the fire, many area vineyards had to abandon their grapes completely. One vineyard reported that “even the birds won’t eat the grapes off the vines!” Some wineries went ahead and made wine, crossing their fingers that it wasn’t disastrous. Some had to dump wine, even after expensive filtering, while others had a “fire sale” and a “$10 release.” Some wineries embraced the year, used it as marketing, highlighting the “slight burnt character,” of the 2003 reserve. A tasting note from the region the following year noted, “a toastiness to the vintage” thinking they must have intensified the toast of the barrels, realizing later that it was from 2003.
Zandberg and Noestheden set out to do field work early on and worked with some local growers to deliberately ‘smoke’ some Cabernet Franc vines. They created an enclosure and exposed the vines and berries to smoke from local fire fuel sources (typical for forest fires in the region) for 60 minutes. They then analyzed the volatile phenols in the grapes at multiple times points, from smoke exposure until harvest and then into the wine. They wanted to elucidate the chemistry and biology of how wine grapes respond to smoke exposure. Winemakers know that grapes grown in smoky conditions may taste okay, even good, but result in smoky-flavored wine. Zandberg, an assistant professor of chemistry, was determined to solve the how and why of this mystery.
The results showed that the volatile phenols increased after smoke exposure and rapidly metabolized and stored in the grape. Concentrations remained constant through the entire development and ripening period. Additionally, they found an increase in total volatile phenols after primary fermentation.
To growers, that means that once the smoke gets into the grapes, it is there to stay. If smoke taint was detectable earlier in the developing berry rather than in the wine, wineries could save themselves the expense of producing a wine of questionable taste.
2017 was a particularly smoky year in the area and despite the poor air quality, the researchers did not find any notable smoke taint in the grapes. Good news for the 2017 vintages! The study also found that visible ash or haze on the grapes is not necessarily indicative of smoke taint.
The UBCO team looked at the impact of potential mitigation strategies, testing whether overhead irrigation may be effective in reducing the effect of smoke exposure. They were somewhat surprised to find that washing or irrigating the grapes did not appear to reduce the concentration of volatile phenols. Once it is in the fruit, it stays in there. They hope to continue to test additional mitigation strategies in the future. Other approaches, such as reverse osmosis have been considered, but winemakers tend to be wary. Often finding that when attempting to remove the bad flavor, the desired character and complexity is also filtered away.
“The compounds are converted by the grape to a form that has sugars attached and they can’t be detected by any current instruments,” said Zandberg. “They also can’t be tasted or smelled. When yeast is introduced, it has enzymes that partially cleave the sugars from compounds, which makes them perceptible again.”
Without early detection, wineries invest tremendous time and money into harvesting grapes that taste untainted, only to find out after fermentation that the wine tastes awful. Making a small test batch of wine is nearly impossible because while waiting 10 days or more for the subjective taste and smell test, the remaining grapes would likely ferment or spoil. Now, Zandberg and Noestheden can provide qualitative results, accurately measured amounts of volatile phenols, within a matter of hours, and winemakers can make informed decisions about whether they should use those grapes at all.
Notably, the technique can also be applied to grapes that have been fermented and aged, measuring the phenol levels in the wine itself, which could be beneficial in determining desired flavor profiles, such as after aging in smoked barrels.
Based on a previous study into smoke taint in Australia, the team at UBCO recognized that the fuel sources of the fires (barley straw and eucalyptus in Australia compared to Ponderosa pine trees in British Columbia) also produce different compounds and have different impacts. Also, because this study controlled the source of the smoke and contained the exposure, unexposed, “control” grapes were only a few yards away and acted as the perfect comparators.
This work is significant to the wine industry, resource management and potential insurance issues related to the loss of a vintage due to smoke taint. The study was in the prestigious Journal of Agricultural and Food Chemistry. Zandberg and Noestheden have presented their work at numerous national and international conferences and symposia. Supporters of the study include industrial partner, Supra Research and Development in Kelowna, British Columbia, the BC Wine Grape Council, and the Natural Sciences and Engineering Research Council.
Zandberg and Noestheden will next tackle connecting analytical chemistry to the senses for a better understanding of the science behind desirable wine characteristics. They hope that highlighting ways to zero in on these traits will take some of the subjectivity out of winemaking.
Growers need answers based on evidence, and they need it sooner, rather than later. Some existing tests for smoke taint claim to provide the solution, but currently, none can detect the effects of complex compounds and sugars until fermentation.
With the recent number of fires and intensity of smoke in many North American wine regions, wine producers needed something to help them manage the impact of smoke in the vineyard. For them, and for the industry, an effective tool in this analytical test could not have come soon enough.
