Smoke taint is strongly correlated with volatile phenols such as guaiacol, 4-methylguaiacol, eugenol, syringol and some cresols, to name a few. These phenols occur in two forms in final wines, a volatile form that can be smelled even before tasting a wine and a glycosylated form that is odourless, but can get transformed to its volatile form by in-mouth enzymes, once the wine is tasted. Generally consumers find smoke tainted wine unacceptable. The associated economic losses are significant for various wine industries around the world that are plagued with bushfires close to vineyards during the summer months, hence all the smoke taint research around the world. The aim of this Canadian study was to evaluate three commercially available agricultural sprays for their ability to lower the uptake of volatile phenols in smoke-exposed grapes.
Three sprays were evaluated:
- Biofilm, an artificial phospholipid cuticle, normally applied to soft-fleshed fruits such as cherries and blueberries to prevent cracking;
- Oil 1, a broad spectrum organic fungicide derived from a petrochemical distillate; and
- Oil 2, a broad spectrum fungicide derived from tee tree oil.
Both oils are currently used on wine grapes, but Biofilm not. The experiment was done with smoked and un-smoked Pinot noir vines. Vines were sprayed one week before the first smoke application, covering grapes and foliage. The vines were smoked twice for a one hour period, with 48 hours between the two smoke applications. Grape samples were taken at five different time points and analysed for free and “acid-labile” volatile phenols. Acid-labile volatile phenols are volatile phenols that have been released from their glycosidic form via acid hydrolysis. This analysis serves as an indication of the amount of glycosidically bound phenols in the grapes that could potentially be released by yeast, bacteria and in-mouth enzymes during winemaking and tasting, causing or enhancing wine spoilage.
- Oil 1 demonstrated no significant difference between treated and untreated smoke-exposed grapes.
- Oil 2 increased volatile phenol concentrations compared to untreated smoke-exposed grapes.
- Biofilm significantly lowered volatile phenol concentrations in treated versus untreated smoke exposed grapes.
SIGNIFICANCE OF THE STUDY
Biofilm, up until now not used on grapes, may have a possible use as a prophylactic spray to prevent smoke taint in wines. However, further studies are needed to evaluate the most effective application programme, cost efficiency, effects of rain, duration of protection and most importantly its impact on fermentation and wine sensory attributes.
James W. Favell, Matthew Noestheden, Sarah M. Lyons, and Wesley F. Zandberg (2019). Development and evaluation of a vineyard-based strategy to mitigate smoke-taint in wine grapes. Journal of Agricultural and Food Chemistry 67 (51), 14137-14142. DOI: 10.1021/acs.jafc.9b05859
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