Color stabilization properties of oenological tannins

Abstract

The use of oenological tannins is authorized for many years by the OIV and advised for color stabilization. For this reason, winemakers look for a better understanding of tannins/anthocyanins interactions to produce deeply colored wines with great color stability during aging. Consequently, the aim of this work, was to verify/confirm the effectiveness of oenological tannins on wine color stabilization to be applied as a new tool by winemakers. 

To achieved this, a model wine solution containing 50 mg/L of malvidin-3-O-monoglucoside was supplemented with 10, 20 and 40 g/hL of commercial tannins (quebracho, ellagitannin, gallotannin, grape-skin and grape-seed) or (-)-epicatechin used as reference. After 1, 7, 14 and 21 days, the full absorbance spectrum (400-800 nm) was measured to determine the CIELAB coordinates and the copigmentation index (new proposed index based on CIELAB parameters). In parallel, samples were injected in HPLC-MS-QTOF to quantified the malvidin-3-O-monoglucoside and its possible degradation products. 

The obtained results show that malvidin-3-O-glucoside concentration decrease during the time accompanied by the formation of two degradation products. However, malvidin-3-O-glucoside decrease differs according to the added tannins meanwhile degradation product formation is the same for all the tannins. In this way, botanical origin of oenological tannins influences their effectiveness. Indeed, gallotanins and grape tannins are the most efficient to improve color stabilization during ageing by copigmentation and by inducing the formation of new polymerized pigments respectively.

Based on this work, oenological tannins have been authorized by the OIV, to stabilize the color of red wines with the modification of the OENO-TECHNO 612 and 613 sheets.