September 2014 Where there s fire, there s smoke. Volume 3 An overview of the impact of smoke taint in winemaking. The 2008 vintage presented a unique challenge for some wine makers. Fires in various northern California counties were pervasive and vineyards located in those areas were exposed to excessive amounts of smoke. As the first samples of smoke-tainted grapes and subsequently the juice and wine came to Enartis Vinquiry, we performed an extensive study to understand the off-characteristics of the wine. Juices with smoke issues were tested via sensory because of the difficulty in separating out the glycoconjugated (bound to sugar) forms of phenolic compounds. This sensory work showed that even in the early life of the grape, smoke compounds were present and affected flavors. The Australians had previously faced this issue and completed the groundwork for deciphering the issues associated with smoke taint. As we again face drought and warm climates in 2014 with an increase in fire incidence, smoke exposure to the vineyard during the growing season may affect grapes in the vineyards of California. Understanding the effects of smoke exposure It is important to understand the effects of smoke exposure on grapevines and the occurrence of smoke attributes in the resulting wine. The Australian Department of Agriculture and Food published key information on grapevine seasonal sensitivity to smoke uptake. Research on Merlot vines was conducted over three seasons where the vines were exposed to smoke at key growth stages in order to understand the smoke-related characteristics in the final wine: 10 cm shoots, flowering, pea size berries, bunch closure, veraison, grapes with intermediate sugar, berries not quite ripe, and harvest. Their research identified three key periods of grapevine sensitivity as: 1. From the period of shoots 10cm in length to flowering: grapevines are low in their sensitivity to smoke. 2. From the period of berries, pea size through to 3 days post veraison: grapevines are variable (low to medium) in their sensitivity to smoke 3. From the period of 7 days post veraison to harvest, grapevines are highly sensitive to smoke. They also found that smoke exposure to grapevines can delay fruit ripening and grapes may have a lower sugar content in comparison to fruit from unaffected vines. This may be due to the effect of smoke in the proper functioning of the grapevine. It was found that a single, heavy smoke exposure for 30 minutes applied at 7 days post veraison and up until harvest was sufficient to create smoke effect in wine. Luckily, it was also determined that there is no carry over from a smoky year to the following vintage, but there could be a potential reduction in crop size. What are the characteristics of smoke effect? Aromas and flavors that are associated with smoke taint can be described as ash tray, smoky, leather, burnt, barbecue, smoked meat, salami and leather. It has been found that volatile phenols are responsible for these smoky attributes. Work done by the AWRI showed that guaiacol ß-D-glucoside and m-cresol ß-Dglucoside in model wine were found to give rise to a smoky/ashy flavor in the mouth. Their study showed that a combination of volatile phenols and their glycosides produces an undesirable smoke flavor in affected wines.
The most common compounds found and their ranges in finished wines noted during testing in 2009 in our laboratory are as follows: Compound Higher Frequency Lower Frequency Sensory Threshold Guaiacol* < 1 to 50 ppb 100 ppb 75 95 ppb 4-methylguaiacol* < 1 to 20 ppb 50-60 ppb 65 ppb * Guaiacol and 4-methylguaiacol derive from the thermal degradation of lignin and exhibit smoky, phenolic, sharp, smoked meat, disinfectant/hospital, and burning aromas and flavors. They are routinely detected in toasted oak barrel aged wines in concentrations up to 20 and 100µg/L. According to the AWRI, these two markers are the most widely used indicator compounds in assessing the degree to which fruit and wines have been affected by smoke (Singh et al, 2011). Because of the presence of glycosylated phenols in grape juice, with subsequent acid hydrolysis, these compounds may increase through fermentation and ageing. This gives rise to the potential that one may not be able to pick up smoke flavors or aromas in the juice stage, but that they will develop through fermentation. Thus, it is important to note that grape handling and winemaking techniques can influence the effect of smoke in an affected wine. Through observation, white wines tend to have lower levels of guaiacol and 4-methylguaiacol and this is perhaps due to the absence or reduced length of skin contact during winemaking. This was indicated by the majority of samples submitted to our laboratory for smokerelated issues being Cabernet Sauvignon, Merlot, Pinot Noir, Syrah, Zinfandel, and some Primitivo. However, it may be that the skin is not the sole source of guaiacol and 4-methylguaiacol because of the presence of the glycosylated precursors which are located in the pulp of the berries exposed to smoke. How to test for smoke taint? Enartis Vinquiry has developed a robust method for the quantification of smoke effect. Interferences due to the complex matrix and adducts of guaiacol and 4-methylguaiacol contributed to the difficulty in the analysis. However, persistence and the insistence on accurate results netted a procedure that measures these markers reliably by GC/MS. Enartis Vinquiry offers analysis for guaiacol and 4-methylguaiacol (Smoke Taint Markers, $120, minimum sample volume 200 ml). How to process affected grapes? After smoke exposure to the vineyard, steps can be taken to minimize the concentration of smoke related aromas, flavors and compounds in the finished wine. The goal is to produce a fresh, fruit-driven wine with round structure in order to reduce the effect of the phenolic compounds.
A. Grape handling/crushing: Hand harvest the fruit to minimize skin rupture and exclude leaf material. Keep fruit cool (50⁰F) and do not allow fruit to macerate in the picking bins. While pressing, use a whole bunch press technique, and separate out free run juice from the heavier press fractions. If you have noticeable ashtray flavors in the juice, we suggest running fining trials to try to mitigate those flavors up front. Enzymes to expedite color extraction in reds and maximize juice yields in whites should be considered. For red wine color extraction and stabilization of anthocyanins and tannins, use Enartis Zym Color Plus. For white wines, use Enartis Zym RS (Rapid Settling) for quick and intense clarification. The use of Enartis Tan Fermcolor at the crusher will help to protect color against oxidation. Follow-up with Enartis Tan Red Fruit and/or Fruitan to bring out notes of berries and red fruit and increase structure is recommended. In white juices, the use of Claril SP, which is a clarifying agent consisting of Bentonite, PVPP, potassium caseinate and silica, can prevent and correct the oxidative phenomena associated with phenolic components of must and wine. Wines treated with Claril SP have more intense, elegant aromas. At yeast inoculation, the use of Enartis Tan Arom will help protect aromas and color, and provide thiol precursors for flavor enhancement. B. Fermentation and Yeast nutrition: According to the Australian Dept. of Agriculture and Food, some yeast strains have been shown to alter smoke-related aromas, flavors and the chemical composition of wine (Ristic 2011). These yeasts are characterized by the production of good fruit and spicy aromas, producing wines in a more elegant, ripe fruit, grand style. It would be wise to minimize fermentation time on skins. The structure of wine can be built by the addition of yeast polysaccharides, oak chips and tannins. We suggest the following: Reds: Enartis Ferm ES 454: Produces unique wines with elegant, ripe fruit and spicy aromas. Enartis Ferm Q5: Intensifies notes of red fruit (strawberry, raspberry, black cherry) and flowers (violet, rose) present in red grapes by using amino acids in juice to produce secondary aromas, esters and higher alcohol. Enartis Ferm Red Fruit: Produces intense secondary aromas, with field berry and violet aromas; blueberry, blackberry, cherry, raspberry, with significant glycerol production. Enartis Ferm Top 20: Produces fermentation esters that enhance fruit character of wine, while respecting varietal character. Whites: Enartis Ferm ES 181: especially recommended for Sauvignon Blanc and other thiolic varieties. Enartis Ferm Q Citrus: Intensifies varietal character by producing zesty and complex notes of citrus (grapefruit), tropical fruit (guava, passion fruit, pineapple), and flowers (jasmine, lime blossom). Enartis Ferm Aroma White: Low fermentation temperatures produce varietal wines with complex mineral, balsamic and citrus; higher temperatures produce aromas of sweet fruit.
Enartis Ferm Top Essence: Enhances aromatic expression of pineapple, passion fruit, banana, grapefruit. Enartis Ferm ES Floral: Given a good source of amino acids, this strain synthesizes delicate white rose and white fruit notes (peach, apricot, pear). Nutriferm Arom Plus supplements precursors which yeast, in the early phase of fermentation, use to make aromatically active compounds. It also provides survival factors which help with yeast viability and thus ensures a successful fermentation. The addition of Nutriferm Advance at 1/3 sugar depletion exerts a detoxifying action, thus assuring optimal aroma cleanliness, and prevents the formation of hydrogen sulfide while maintaining efficient sugar transport systems until the end of fermentation. C. Improvement of mouthfeel post-fermentation: Winemaking with smoke-affected grapes requires that extraction practices be limited, so structure will need to be rebuilt in the wine during and/or following fermentation. There are so many options, and each and every wine is different, so please contact your Enartis Vinquiry representative to set-up bench trials. D. Methods of remediation: Many techniques in the industry have been tried to remove smoke taint. Reverse osmosis has been found to be effective in reduction, but the smoke-related characteristics return to the wine over time. In the many trials we performed in-house, our personal preference, along with our clients, was the combination of fining, followed by the addition of tannins and/or polysaccharides to increase structure and mouthfeel., an activated carbon, was effective in reducing levels of the smoke taint markers. Trials performed in 2010 on wines from 2008 that had been affected with smoke-taint showed the effectiveness of to significantly reduce volatile phenols, resulting in overall improved wine aroma without affecting color. 40 Guaiacol (ppb) 4-methylguaiacol (ppb) 35 30 25 20 15 10 5 0 PN08-1 PN08-1 + 20 g/hl PN08-1 + 40 g/hl PN08-2 PN08-2 + 20 g/hl PN08-2 + 40 g/hl
We hope that this information helps you to make informed decisions regarding that hopeless moment when you realize there is a smoke effect in your grapes. If you have any questions, please give us a call at (707) 838-6312. References: Australian Journal of Grape and Wine Research, Volume 17 Number 2, 2011: Singh et al., Ristic et al., Kennison et al. Kennison, K., Ward, G., Fisher, D. (2011) Key Information on Smoke Effect in Grapes and Wine: What can be done to identify and reduce smoke effect in grape and wine production? Department of Agriculture and Food, Government of Western Australia.