Color of Riesling and Vidal Wines as Affected by Bentonite, Cufex®, and Sulfur Dioxide Juice Treatments

Abstract

Browning has been controlled by sulfur dioxide (SO₂) in wine for many years, but other compounds also have the potential to reduce browning. Bentonite, Cufex® and SO₂ were applied to juice from Riesling grapes <i>Vitis vinifera</i> L. and Vidal grapes, a French-American Hybrid to compare their effects on wine browning. Seven treatments (control, 35 mg/L SO₂, 70 mg/L SO₂, 120 mg/L bentonite, 240 mg/L bentonite, 90 mg/L Cufex and 150 mg/L Cufex) were applied to the juice. Two levels of SO₂ (0 and 20 mg/L) and two storage times (initial and 3 months at 37°C) were established on each of the seven treatments after fermentation was complete. The SO₂ juice treatments resulted in the least browning (absorbance at 420 nm), and bentonite and Cufex treatments were also less brown than the control. Sulfur dioxide juice treatments and SO₂ at bottling increased green and reduced yellow color as was shown by lower Gardner Color Difference meter 9a9 and 9b9 values. The addition of 20 mg/L SO₂ at bottling further decreased browning but was more effective in Riesling than in Vidal wines. Three months storage at 37°C increased browning almost two-fold as compared to initial readings.