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.

-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.

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.