Research in Plain English (RIPE)
Retaining Tannins in Blends of Vinifera and Hybrid Grapes – Co-Ferment or Ferment, Separate and Blend?
Erin L. Norton, Gavin L. Sacks, and Joey N. Talbert
Am J Enol Vitic. January 2020 71: 26-32; published ahead of print September 13, 2019; DOI: 10.5344/ajev.2019.19032
By Michelle Podolec
- Wines made with red interspecific hybrid cultivars have lower tannin concentrations than wines made with V. vinifera cultivars due to lower grape tannin and higher concentrations of tannin-binding proteins
- Blending high-tannin vinifera into low-tannin hybrids will increase wine tannin, but the amount of tannin retained depends on whether blending is done before or after fermentation and racking. In this work, when small amounts of vinifera (Cabernet Sauvignon) were co-fermented with a hybrid (Marquette) at a 10-90 ratio, the final tannin concentration was lower than expected based on the varietal wines. This decrease in wine tannin was not observed when wines were blended after fermentation and racking.
- This loss of tannin when hybrid and vinifera grapes are blended pre-fermentation may be due to the high levels of protein in the hybrid.
- Winemakers who intend to increase tannin in hybrid wines by blending with vinifera grapes should avoid co-fermentation and blend post-fermentation to maximize tannin retention.
Interspecific hybrid grape cultivars (Vitis spp.) are widely grown in Eastern North America. In particular, so-called “cold-climate” cultivars (such as Frontenac and Marquette) are being widely planted in the upper Midwest, because they survive low midwinter temperatures. However, the red wines they produce have lower tannin concentrations and astringency than red wines produced from European wine grapes (V. vinifera).
The lower concentrations of tannins in hybrid wines are due to lower skin tannins and higher concentrations of extractable proteins. Adding commercially available tannins to the wines has not been as effective as winemakers had hoped. Too frequently tannin additions led to brown colors, off-aromas, or bitterness. Blending has been investigated as a potential solution, but results have been inconsistent—often the extra tannin is not retained.
Researchers hypothesized that tannin retention would be lower when co-fermenting (CF) low tannin, high protein hybrid grapes with high-tannin, low-protein vinifera grapes than the two varieties were vinified separately and blended after fermentation.
- Cabernet Sauvignon (vinifera, high tannin) and Marquette (interspecific hybrid, low tannin) were used to make blended wines.
- The two varieties were blended in varying proportions prior to fermentation and co-fermented, or else the two individual varieties were fermented separately and blended after fermentation.
- Tannins and proteins in resulting wines were measured, both in varietal, unblended wines and the co-fermented and post-fermentation blends.
Conclusions and Practical Considerations
Most blends of Cabernet Sauvignon and Marquette had tannin concentrations similar to values expected based on concentrations in the varietal wines, regardless if the wine was co-fermented or blended post-fermentation. However, the wine produced by co-fermenting with the highest proportion of Marquette (90%) had significantly lower tannin than expected. This decrease in tannin was not observed for the post-fermentation blend. . The researchers hypothesize this was caused by binding of tannin by insoluble Marquette grape proteins during co-fermentation.
For producers wanting to increase tannins to enhance mouthfeel by blending with a high-tannin grape such as Cabernet Sauvignon, post-fermentation blending will result in higher tannin retention than co-fermentation.
Michelle Podolec is extension support specialist with the statewide viticulture extension program, based at Cornell AgriTech in Geneva, NY.