Amanda Fleming and Renee Threlfall*
*University of Arkansas System Division of Agriculture, 2650 N. Young Ave, Fayetteville, AR, 72704 (rthrelf@uark.edu)

While Vitis vinifera grapes are used predominantly for wine production, muscadine grapes (Vitis rotundifolia Michx.), native to the southeast United States, are also used but can have issues with color and phenolic stability. Cofermentation, two or more grape varieties fermented together, can enhance wine phenolic stability. Furthermore, sulfur dioxide (SO₂) additions in wines can affect color. In 2023, Noble (Vitis muscadinia) and Merlot (V. vinifera) grapes were harvested from commercial vineyards, randomized into five cofermentation treatments in duplicate (100% Noble; 75% Noble + 25% Merlot; 50% Noble + 50% Merlot; 25% Noble + 75% Merlot; and 100% Merlot), processed, and fermented. At bottling, SO₂ was added to each cofermentation treatment at different molecular levels (0.0, 0.8 and 1.5 mg/L). At bottling, wine pH (3.24 to 3.67), titratable acidity (0.60 to 0.80%), free SO₂ (18.53 to 42.43 mg/L), and ethanol (10.35 to 13.64%) varied for each cofermentation treatment. The cofermentation × SO₂ interaction was significant for L*; 100% Noble without SO₂ had the lowest L* and 100% Merlot with 1.5 mg/L SO₂ had the highest. As Noble increased in each cofermentation treatment, red color, brown color, color density, total phenolics, and total anthocyanins increased. Wines without SO₂ had more red and brown color and greater color density than wines with 0.8 or 1.5 mg/L SO₂. Wines with 100% Noble had the highest total phenolics (2037 mg gallic acid/L) and total anthocyanins (1712 mg/L) compared to 100% Merlot (884 mg gallic acid/L and 296 mg/L, respectively). At bottling, wines with ≥25% Noble had higher color and phenolic content than 100% Merlot wines. Furthermore, SO₂ had more effect on L* in cofermentation treatments with more Merlot than Noble. Blends with more Merlot had more SO₂ bleaching, with lower phenolic and color content at bottling, while wines cofermented primarily with Noble grapes had darker color and more phenolics at bottling.

Funding Support: Southern Region Small Fruit Consortium Grant