A Technical Guide for Wine Producers

RECENT ARTICLES   |   WYNBOER HOME WHAT'S UP IN THE VINEYARD AND CELLAR The retention of flavour compounds in white wines Charl Theron Wines from the so-called new world wine countries are well-known for and popular mostly because of their fruitiness. Loss of flavour in young white wines especially is therefore a source of concern for South African winemakers and different practices are being adopted to address the problem. The oxidation of young white wines usually takes place in two stages. Firstly there is a transformation process of the flavour compounds, resulting in losses of the wine’s unique flavour profiles. This goes hand in hand with the formation of other flavour compounds associated with maturation or taint. Secondly a browning process is observed. Wines contain many phenolic compounds, which, being anti-oxidants, are able to offer natural protection against oxidation. It has been reported, for example, that both caffeic and gallic acid are able to inhibit flavour degradation in white and red wines during oxidative storage. Amino acids and peptides also act as inhibitors to browning in a wide variety of food products. In this regard glutathione is one of the most active compounds. In the wine industry sulphur dioxide is generally used as a preservative and an anti-oxidant, but above certain values it may impact negatively on flavour and some consumers also experience negative health effects such as asthma. There is consequently a general trend to keep the sulphur dioxide levels of wines 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 influences 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 easily. The two different levels of sulphur dioxide used in the study were 35 mg/l free and 143 mg/l total, compared 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 the wines. The different caffeic acid and glutathione additions involved 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 various periods of time. Different flavour compounds were analysed at different stages. The findings of the project may be summarised as follows: Wine samples with the two different sulphur dioxide levels display similar concentrations of flavour compounds. Sulphur dioxide does not seem to play a cardinal role in the protection of flavour compounds 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 the lower sulphur dioxide content. This includes, amongst others, important esters such as isoamyl acetate, ethyl caproate, ethyl caprilate, ethyl caprate and linalol. The inhibiting effect of caffeic acid and glutathione on the loss of flavour compounds is most likely due to their anti-oxidant properties (Roussis et al, 2007). Caffeic acid and glutathione are natural ingredients of wine. Caffeic acid’s ester with tartaric acid, caphtaric acid, is predominant in grapes. With ripening of grapes and during fermentation glutathione increases to values of 2 to 5 mg/l. Presently in South Africa the addition of none of these components is allowed during vinification. Reference: Roussis, I.G., Lambropoulos, I. & P. Tzimas. 2007. Protection of Volatiles in a Wine with Low Sulfur Dioxide by Caffeic Acid or Glutathione. Am. J. Enol. Vitic. 58(2): 274 - 278.

Wynboer is incorporated in WineLand, magazine of the SA wine producers. Subscribe to WineLand Visit our sister sites: South African wine farmers' representative organisation Facts, figures, contact details and much more in the 2009/10 Directory

UP	COPYRIGHT (C) 2000 WineLand