Small scale winemaking trials utilising Riesling musts were used to investigate the possibility of producing organic style wines without the use of SO₂. The main objective was to determine the effect of hyperoxidation and oxygen scavenging by glucose oxidase, on the quality and stability of wines produced without SO₂. Wines produced without S0₂ but employing hyperoxidation developed more visible colour ("brown" hue) than wines produced with SO₂, and less visible colour than wines produced without SO₂. The addition of glucose oxidase at bottling further reduced colour development in both treatments without S0₂, however the wines had increased colour ("yellow" hue) than wine produced with SO₂. These visual observations corresponded with the spectrophotometric measurements of browning (A420nm) and pinking (A520nm) in the wines.
The wines produced without SO₂ (+/- hyperoxidation) had a lower total phenol content and specifically less caftaric acid, than wines with SO₂. Glucose oxidase (GOX) did not have any effect on the phenol content. Therefore, the decrease in phenols occurs primarily in the juice due to oxidation reactions, when the juice is not protected by SO₂.
After 3 months bottle storage all the wines produced without SO₂ displayed an oxidative "aldehyde like" characteristic with a loss of fruit and floral aromas. The wines that contained GOX had retained more fruit aroma and the hyperoxidation treatment was fresher and had more fruit aroma than the treatment without SO₂, but they all had less fruit aroma than the treatment with SO₂. After 6 months storage the wines showed similar aroma profiles to those observed at 3 months.
Measured increases in acetaldehyde did not correspond with the changes in dissolved oxygen. Wines produced with SO₂ appeared to developed little or no acetaldehyde, any acetaldehyde produced is bound by the SO₂. The wines without SO₂ did develop acetaldehyde. GOX reduced dissolved oxygen in wines at 3 months, but not at 6 months. GOX appeared to result in increased levels of measured, but not perceived acetaldehyde.
Protein stability to heat/cold testing of the wines produced by hyperoxidation was visually better than for wines produced with SO₂. The wines from hyperoxidised musts were higher in residual sugar and lower in T A than wine produced with S0₂. GOX had no significant effect on sugar or acidity. Alcohol was not affected by production with or without SO₂.
In practical terms this research has demonstrated that wines produced without SO₂ are likely to have a short shelf life (<3 months). The use of hyperoxidation and GOX at bottling may extend this to at least 3-6 months. However, a limitation that was observed was that once bottled wines were opened they were susceptible to oxidation, but this effect was less pronounced in the hyperoxidation and GOX treatments.[Show full abstract]
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