Cool Climate Winemaking: Exogenous Tannin Additions In Red Hybrid Cultivars
The addition of exogenous tannins has become a common practice in cool climate winemaking to increase tannin content in hybrid red wines. These additions, when made at recommended rates and times, often result in low tannin retention. Previous research has shown that various phenolic compounds have a mixed effect on lactic acid bacteria (LAB) growth and malolactic fermentation (MLF) success. This study examined the effect of exogenous tannin additions above recommended rates on two strains of LAB during MLF in hybrid sp. Corot noir, Noiret, and Marquette cultivars. A mixed effects model was used to determine the interactions of LAB and tannin additions on MLF, independently and together. In all cultivars there were interaction effects, varying among cultivars, indicating that LAB strain selection and tannin additions have an effect on MLF. Despite these effects, all lots finished MLF in two weeks or less, suggesting that the addition of the exogenous tannins studied may not impact completion of MLF when other conditions are optimal. Further, little research has been performed on the timing of exogenous tannin additions in hybrid red wine. In 2013, wines were made from Maréchal Foch, Corot noir, and Cabernet Franc to compare the retention of exogenous tannins in interspecific hybrids and Vitis vinifera. In each cultivar a commercial exogenous tannin product containing [ALMOST EQUAL TO]38% condensed tannin was added at a rate of 800 mg/L. Additions were made at each major processing step for a total of 3 additions treatments during the winemaking process. To determine the fate of tannins in each wine, a mass balance was performed tracking the loss and gain in tannin. With later additions, there was a progressive increase in retention for all cultivars, suggesting that adding tannin after alcoholic fermentation reduces the portion lost. Mass balance calculations also showed that 5-10 times more tannin was lost in the lees between post alcoholic fermentation (AF) and post malolactic fermentation (MLF) samples than following MLF through eight months of aging. This suggests that in the hybrid red cultivars studied, later additions of exogenous tannin increase condensed tannin retention to levels comparable to that in V. vinifera. The recommend dosage for exogenous tannins of 50-500 mg/L may not effectively increase condensed tannins. In 2013, wines were made from Maréchal Foch, Corot noir, and Cabernet Franc to compare the retention of exogenous tannins in interspecific hybrids and Vitis vinifera. After analyzing 12 commercial tannin products for condensed tannin concentration via HPLC, the highest, with a concentration 38%, was added at a rate of 400, 800, and 1200 mg/L after crush/before yeast inoculation. A separate portion of each cultivar was pressed off the skins immediately, fermented with 1600 mg/L of exogenous tannin, then back-blended postfermentation with a control wine for a final theoretical concentration of 400 mg/L tannin addition. At bottling, tannin concentrations in all treatments were higher than the respective control, but none exceeded 50% retention. This suggests that high concentration additions of exogenous tannin increase the condensed tannins in hybrid red wines, but retention rates vary by cultivar.
Vanden Heuvel,Justine E.
Food Science & Technology
M.S. of Food Science & Technology
Master of Science
dissertation or thesis