Pre-fermentation tannin addition enhances volatile thiol content of white wines
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By Karien O'Kennedy
The aim of this study was to examine the role of volatile thiols in the aroma Gewürztraminer wines, as well as the potential use of oenological grape tannin extracts as a source of thiol precursors.
500 kg of each of Gewürztraminer and Sauvignon blanc grapes were harvested in Trentino, Italy. Both grape varieties were fermented with VL3 (Laffort) and VIN 13 (Anchor Yeast) and both were treated with two types of tannins: one low in thiol precursors (Erbslöh) and one high in thiol precursors (Enartis). Tannin additions were done pre-fermentation and proper controls where no tannin addition was done were kept. In a second trial fermentations with VIN 13 only received tannins post-fermentation.
Initial juice analysis:
The two juices contained similar concentrations of the GSH-3MH precursor.
The S. blanc juice had double the amount of Cys-3MH precursor than the Gewürztraminer juice.
Both varieties had more GSH-3MH than Cys-3MH.
Effect of tannin treatments:
- Tannin low did not increase thiol precursors or final volatile thiol content of both wines.
- Tannin high increased both precursors in both juices.
- Tannin high increased the 3MH content of both wines but the 3MHA only in the Gewürztraminer.
- Tannin addition post fermentation is not nearly as affective as tannin addition pre-fermentation.
- Post-fermentation treatment still increased the 3MH concentrations but decreased the 3MHA concentrations compared to the controls.
- Sensory analysis performed on the Gewürztraminer wines treated with tannin low and high pre-fermentation and fermented with VIN 13 confirmed that only tannin high significantly enhanced the grapefruit character in the final wines.
Significance of the study:
Pre-fermentation addition of commercial tannin extracts high in thiol precursors can enhance the final volatile thiol content, as well as the aroma, of Gewürztraminer and S. blanc wines. Care should however be taken to manage the extra phenolic compounds added to the juice and present in the final wines, in order to protect the wines against oxidation.