Postharvest ozone fumigation of Petit Verdot grapes to prevent use of sulphites


The aim of this research was to evaluate the application of ozone as a sanitizing agent of grapes before vinification, in order to reduce the use of sulphur dioxide.

Project layout: 
-500 kg of Petit Verdot grapes were hand harvested and placed in perforated boxes (60 x 40 x 30 cm);
-Boxes were placed in a cold room overnight where grapes were fumigated with ozone;
-Control grapes were also packed in perforated boxes and placed in a cold room;
-Control grapes were powdered with potassium metabisulfite – without any specific calculation – to lightly cover the top layer of bunches;
-Both batches were vinified the next day. Refer to article for winemaking protocol.

Results: 
-Ozone treatment did not affect sugar concentration, TA or pH of grapes;
-Overnight cold storage also had no effect on TA, pH or sugar concentration in the control;
-Ozone significantly increased concentration of anthocyanin (19% increase) and skin tannin (14%);
-Ozone significantly reduced acetic acid bacteria, lactic bacteria and yeasts;
-Fermentation of juice from ozone treated grapes was faster (10 days vs 16 days);
-The onset of fermentation was immediate (as opposed to 3 days in the control) since the inoculated yeast had less microorganisms to compete with;
-Ozone treatment increased the extractability of phenolic substances and anthocyanin and wines had a higher TA;
-pH and VA of final wines were not significantly different between treatments;
-Wine from ozone treated grapes scored higher than the control, especially in terms of colour and aroma.

Significance of the study: 
This study shows that postharvest ozone fumigation can be used to produce wine without sulfur dioxide.

Reference: 
Bellincontro, A.Catelli, C.Cotarella, R., and Mencarelli, F. (2017Postharvest ozone fumigation of Petit Verdot grapes to prevent the use of sulfites and to increase anthocyanin in wineAustralian Journal of Grape and Wine Research23200206. doi: 10.1111/ajgw.12257.



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