Glutathione is an Antioxidant

Here is the problem. We were always planning to do a "benign neglect oxidation" of the pressed must and then leave it to cold soak overnight to settle out the gross lees, but when I read in an older issue of Practical Winery & Vineyard (May/June 2010) an article called "Sauvignon Blanc: Impact of Fining Treatment on Juice Quality" I started to have second thoughts.
The article in Practical Winery & Vineyard presented experiments that showed the benefits of glutathione, a tripeptide consisting of glutamine-cysteine-glycine as being a better antioxidant than ascorbic acid or sulfur dioxide when the press fraction of the must is treated in a reductive environment.¹

In benign neglect hyperoxidation, the initial press fraction is left in an oxidative environment and the glutathione is free to react with the phenols in the must. The fate of the glutathione is enumerated in a previous blog called Hyperoxidation Revisited. There were five experiments carried out in South Africa and Bordeaux:

• Case Study 1: Reductive handling of all fractions
  (Durbanville, South Africa)
• Case Study 2: Reductive handling of all fraction
  (Stellenbosch, South Africa)
• Case Study 3: Oxidative handling of press fraction
  (Stellenbosch, South Africa)
• Case Study 4: Comparison between reductive and oxidative handling (Bordeaux, France)
• Case Study 5: Comparison between fining agents with reductive handling (Bordeaux, France)

In the above studies, it was shown that reductive handling in the absence of added SO₂ gave the best levels of glutathione. Oxidative handling of the press fractions resulted in the diminishing of glutathione levels. However, in the declining phases of fermentation when ethanol levels are increasing, the article written by Schneider, Must Hyperoxidation A Review, mentions that oxygen is key to enabling yeast survival.So, what to do. I'll have to read more about the benefits of glutathione (I'll report back), but we'll probably end up doing several "wine experiments" when we get our grapes!

1. Paul K. Bowyer (Technical Manager, Laffort Australia), Marie-Laure Murat (Lab Manager, Sarco, France), and Virginie Moine-Ledoux (Research Director, Laffort), "SAUVIGNON BLANC: Impact of fining treatments on juice quality", Practical Winery & Vineyard, May/June 2010, pg. 25-33.
2. Wikipedia image of Glutathione. All structures were drawn by the freely available drawing program from ACD Labs called ACD/ChemSketch Freeware.