Managing Tannins in the Winery. AVF Project #2025-2978.
Summary of Progress:
To further investigate the structural changes to grape tannins and the impact on grape tannin concentration by glutathione additions, an experimental design was carried out with red wine made to two separate maceration lengths and glutathione added at multiple time points throughout the winemaking process. Cabernet Sauvignon grapes were harvested from Cold Creek Vineyard on October 7, 2025, and the fruit processed at the Wine Science Center. For the control maceration wines, pressing occurred 14 days after crush, pharmaceutical-grade reduced glutathione was added on day 15 and day 45 post-crush to three 60 L kegs of wine at each addition. For extended maceration wines, tanks with wine still on skins and seeds were combined for extended storage on day 13 after crush, reduced glutathione added on day 15 to three of the 210L tanks, sealed on day 16, and stored blanketed with inert gas. Extended maceration wines were then pressed 44 days after crush, and reduced glutathione added at day 45 to three additional extended maceration wines in 60L kegs. Glutathione was added to each tank or keg at a concentration of 2mM. Thus far phenolic measurements using traditional assays show early additions of glutathione have minimal impact on protein precipitable tannin concentration. In our previous experiments glutathione was added post-fermentation so this result was anticipated, and we have planned future additional treatments. Overall, the current experiment has highlighted the potential importance of addition timing on the effectiveness of glutathione modification of tannins and has created a clear investigative route for lab scale experiments with regards to tannin modification and reduction.
Disappointingly we have been hampered with operational setbacks that have prevented us from doing our lab scale experiments and utilizing more sophisticated analysis on the winemaking treatments such as mass spectrometry. We expect to carry out these experiments in early 2026 to remain on track for our objectives.
Eighteen Cabernet Sauvignon wines were made during the 2025 vintage varying the length of maceration with glutathione additions made during stages of maceration and wine development to evaluate its impact. Thus far we have seen limited impacts using traditional assay methods. Overall, the current experiment has highlighted the potential importance of addition timing on the effectiveness of glutathione modification and has created a clear investigative route for evaluating glutathione at lab scale with regards to tannin modification and reduction.
