Background and Aims
The request by the consumer for safer food is also pushing the wine sector to find alternative solutions to sulfur dioxide. The aim of this research has been to evaluate the application of ozone as a sanitising agent of grapes before vinification in order to avoid the use of sulfur dioxide.
Methods and Results
Postharvest ozone fumigation overnight of Petit Verdot grapes increased anthocyanin concentration by 19% versus 9% in the Control (untreated) during fermentation/maceration. Fermentation kinetics were faster in wine made from ozone‐treated grapes (16 vs 21 days for the Control), and extraction of phenolic substances and anthocyanin was more rapid than that in the Control wines, Ozone treatment significantly reduced the count of Saccharomyces cerevisiae and non‐Saccharomyces yeasts but also significantly decreased the acetic acid bacteria. The final wine produced from ozone‐treated grapes was characterised by low volatile acidity (similar to that of the Control wine) with a significant reduction in sulfur dioxide (17 and 8 mg/L, respectively, total and free sulfur dioxide). Sensory evaluation revealed a strong fruity aroma.
Conclusions
Ozone gas treatment of grapes reduced the microbial count significantly and increased the extraction of phenolic substances and the aroma of the final wine.
Significance of the Study
Postharvest ozone fumigation can be used to produce wine without sulfur dioxide.
When bushfires occur near grape growing regions, vineyards can be exposed to smoke, and depending on the timing and duration of grapevine smoke exposure, fruit can become tainted. Smoke-derived volatile compounds, including volatile phenols, can impart unpleasant smoky, ashy characters to wines made from smoke-affected grapes, leading to substantial revenue losses where wines are perceivably tainted. This study investigated the potential for post-harvest ozone treatment of smoke-affected grapes to mitigate the intensity of smoke taint in wine. Merlot grapevines were exposed to smoke at ~7 days post-veraison and at harvest grapes were treated with 1 or 3 ppm of gaseous ozone (for 24 or 12 h, respectively), prior to winemaking. The concentrations of smoke taint marker compounds (i.e., free and glycosylated volatile phenols) were measured in grapes and wines to determine to what extent ozonation could mitigate the effects of grapevine exposure to smoke. The 24 h 1 ppm ozone treatment not only gave significantly lower volatile phenol and volatile phenol glycoside concentrations but also diminished the sensory perception of smoke taint in wine. Post-harvest smoke and ozone treatment of grapes suggests that ozone works more effectively when smoke-derived volatile phenols are in their free (aglycone) form, rather than glycosylated forms. Nevertheless, the collective results demonstrate the efficacy of post-harvest ozone treatment as a strategy for mitigation of smoke taint in wine.
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