SO₂ consumption in white wine oxidation: approaches to low-input vinifications based on rapid electrochemical analyses and predictive enology

Abstract

Oxidative stability is a critical factor in wine shelf-life. SO₂ is commonly added to wine due to its strong antioxidant activity, although there is a general push to reduce SO₂ use in vinification. Reducing the reliance on SO₂ while maintaining oxidative stability is a pressing challenge for winemakers, emphasizing the need for predictive tools to optimize wine oxidation management.

In this study, the relationship between O₂ and SO₂ consumption of 71 Lugana white wines was studied. Samples underwent controlled oxidation (oxygen consumed ~ 5ppm at 20°C), while control anoxic samples were stored in the same conditions. Samples were characterized for SO₂ content before and after oxygen consumption, ammonia, primary amino nitrogen (PAN), polyphenols, ascorbic acid, and catechins. Cyclic voltammetry was used to obtain information on the redox-active compounds present in the wines.

Oxygen consumption rate followed first-order kinetics, with half-lives ranging from 2.1 to 18.1 days Wines with ascorbic acid >10 mg/L showed half-lives consistently below 9 days. In contrast, wines with low ascorbic acid <10 mg/L exhibited high variability, with some consuming oxygen rapidly, reaching half-lives as low as 4 days. SO₂ consumption ranged from 1.4 to 18 mg/L in the oxygenated samples and from 0.6 mg/L to 14.9 mg/L in the anoxic samples. Final free SO₂ concentrations showed a strong correlation with their initial values in both oxygenated and anoxic samples. On average, oxygenated samples consumed 4.6 mg/L more free SO₂ compared to anoxic samples, with a ratio of 0.92 mg of free SO₂ consumed per mg of O₂. Notably, variability among individual samples was substantial, with ratios ranging from 0.62 to 1.95 mg free SO₂/mg O₂.

The amount of free SO₂ consumed in oxygenated samples was significantly inversely correlated with the half-life, suggesting that, under equal oxygen availability, wines with faster oxygen consumption tend to consume less free SO₂. Electrochemical profiles also revealed significant variability among the redox-active compounds of the different wines, particularly in the voltametric regions located around 420mV 820mV.

Different modelling approaches were explored to identify opportunities for the development of predictive tools for SO₂ stability. Results of these investigations will be presented, with particular emphasis on the possibility to leverage electrochemical data to develop a rapid and reliable method to estimate oxidative stability without the need for extensive chemical analyses.

By combining rapid electrochemical analysis and predictive modelling, more rational use of SO₂ appears possible, contributing to more efficient and sustainable wine management practices.