White Table Wine Quality and Polyphenol Composition as Affected by Must SO₂ Content and Pomace Contact Time

Abstract

Dry white table wines were made from Chardonnay, Chenin blanc, French Colombard, and Semillon grapes following 0, 3, 6 and 12 hours holding of the destemmed, crushed grapes before juice separation and with additions at crushing of zero, low (50 mg/L), intermediate (100 mg/L) and high (200 mg/L) levels of SO₂. A fifth series, making 20 wines per variety, had zero added SO₂ and was bubbled with oxygen gas throughout holding.

These oxygenated musts browned severely, but when finished the wines tended to be slightly less brown, more resistant to further browning, less fruity, and lower in general quality than the comparable (zero SO₂) nonoxygenated wines. Deliberate oxidation of musts is concluded to be undesirable, even though it was possible to decrease the phenolic browning substrate in the wine by this procedure.

Added SO₂ was bound during fermentation, of course, and the free SO₂ in the wine was nearly the same whether SO₂ had been added or not. Furthermore, during pomace contact the total SO₂ was rapidly lowered. Increased pomace contact and increased SO₂ increased extraction of total phenol, specifically the flavonoid fraction, from the pomace into the wine and increased absorbance at 280 and 320 nm by the wines. Absorbance at 420 nm and the capacity to brown further were directly related to pomace contact and inversely to added SO₂. Increased pomace contact increased the wines' pinking upon exposure to oxygen and low levels of added SO₂ encouraged, while high levels discouraged, such pinking. Astringency or bitterness differences were not large or consistent enough to be meaningful except for increased bitterness at the highest level of pomace contact. Fruitiness and general quality were affected similarly, being improved by low to intermediate levels of SO₂ addition to the must and generally harmed by appreciable pomace contact. However, the optimum pomace contact appeared to be zero only for Chenin blanc and increased for the others in the order French Colombard, Chardonnay, and Semillon.