A Technical Guide for Wine Producers

RECENT ARTICLES   |   WYNBOER HOME WHAT'S UP IN THE VINEYARD AND CELLAR The retention of flavourants in white wines by Charl Theron The popularity and renown of wines from the so-called New World wine countries may be ascribed mainly to their fruitiness. Loss of flavour in young white wines particularly is disconcerting to South African winemakers and various practices are being adopted to address this problem. The oxidation of young white wines usually occurs in two stages. Firstly a transformation process of the flavourants takes place, resulting in losses of the wines’ unique flavour profiles. This is accompanied by the formation of other flavourants associated with maturation or spoilage. Secondly a browning process takes place. Wine contains numerous phenolic compounds; being anti-oxidants, these are able to offer natural protection against oxidation of the wine. It has been reported, for example, that caffeic and gallic acid are able to inhibit the flavour degradation of white and red wines during oxidative storage. Amino acids and peptides are also inhibitors of browning in a wide range of food products. Glutathione is one of the most active compounds in this regard. Sulphur dioxide is commonly used as a preservative and anti-oxidant in the wine industry, but above certain amounts it may have a negative impact on flavour and some consumers with health problems such as asthma can suffer complications. The general trend is therefore to keep the sulphur dioxide levels of wine as low as possible. A project was launched in Greece to determine how the use of caffeic acid and/or glutathione combined with sulphur dioxide impacts on the flavour concentrations of white wines during storage. A 2004 white wine made from Debina was used in the study. Debina is a late cultivar and the wines oxidise readily. The two different sulphur dioxide levels used in the study were 35 mg/l free and 143 mg/l total as opposed to 55 mg/l free and 166 mg/l total. Ascorbic acid at a concentration of 90 mg/l was a standard addition to all wines. The various caffeic acid and glutathione additions comprised 60 mg/l caffeic acid, 20 mg/l glutathione and a combination of 30 mg/l caffeic acid and 10 mg/l glutathione respectively. Wines were stored at 20°C in a dark room for varying periods of time. Various flavourants were analysed over the different periods. The findings of the project can be summarised as follows: Wine samples with the two different sulphur dioxide levels have similar concentrations of flavourants. Sulphur dioxide apparently does not play a key role in the protection of flavourants during storage. The addition of caffeic acid and glutathione or combinations thereof prevents losses of several volatile esters and terpenes during the storage of wines with a lower sulphur dioxide content. This includes, inter alia, important esters such as isoamyl acetate, ethyl caproate, ethyl caprilate, ethyl caprate and linalol. The inhibiting effect of caffeic acid and glutathione on flavour losses can probably be ascribed to their anti-oxidant characteristics (Roussis et al., 2007). Caffeic acid and glutathione are natural ingredients of wine. Caffeic acid’s ester, with tartaric acid and caphtaric acid, predominates in grapes. Glutathione increases to quantities of 2 - 5 mg/l with ripening of grapes and during fermentation. At present in South Africa none of these components may be added during vinification. Reference Roussis, I.G., Lambropoulos, I. & Tzimas, P. 2007. Protection of Volatiles in a Wine with Low Sulfur Dioxide by Caffeic Acid or Glutathione. Am. J. Enol. Vitic. 58(2): 274 - 278.

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