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A Technical Guide for Wine Producers
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EFFECT OF FERMENTATION TEMPERATURE ON PINOTAGE WINE COMPOSITION AND QUALITY INTRODUCTION Over the past few years Pinotage has become a sought after local and export product, due to its South African uniqueness and the dedication of certain winemakers. The wine industry, and the Pinotage Association in particular, are currently endeavouring to improve quality and have launched a marketing drive. Research is an important component of this strategy. Various viticultural and oenological factors influence Pinotage wine quality and research is currently in progress to investigate some of these factors. One of the most important factors in the course of vinification is the fermentation process and in particular the temperature during fermentation. Fermentation temperature can have a prominent effect on the formation of fermentation aromas such as esters and higher alcohols. These components are especially important where more complex wines have to be made from grapes of neutral cultivars. In the past Pinotage wine quality was impaired when aromatic fermentation flavours were too intense, especially in the case of iso-amylacetate (the so-called "duco" character). One of the preventative measures is to move away from fermentation temperatures that are too low, so that the grape-oriented berry flavours can become more prominent. The purpose of this research was consequently to determine the effect of fermentation temperature on Pinotage wine composition, in this case esters and higher alcohols, and wine quality. MATERIAL AND METHODS The experiment was conducted on a commercial scale at Simonsig during the 1997 and 1998 seasons. In both instances Pinotage grapes were harvested at approximately 24°B and divided evenly among four rotor tanks (± 12 000 kg per tank). The experiment was conducted in duplicate. In 1997 the grapes of two rotor tanks were fermented at 24°C and the other two at 28°B. In 1998 the experiment was conducted on the same basis at 28°C and 32°C. After three to four days' fermentation with WE 14 (until approximately 6°B in 1997 and approximately 0°B in 1998), the skins were pressed, the juice racked and further fermented dry at 20°C. Thereafter malolactic fermentation occurred and the wines were then handled according to standard cellar practices. The wines were analysed gas chromatographically for esters and higher alcohols, and evaluated sensorially for quality (fruit intensity, berry/plum intensity and overall quality). In 1997 no distinction was made between fruity/estery and berry/plummy flavours and these were evaluated together as aroma intensity. RESULTS AND DISCUSSION During the 1997 season the lower fermentation temperature (24°C) produced higher concentrations of esters and higher alcohols than the 28°C fermentations (Fig. 1). In 1998 the lower fermentation temperature (in this case 28°C) once again produced higher concentrations of acetate esters and higher alcohols than the higher fermentation temperature (32°C) (Fig. 2). However, the ethyl esters (hexanoate, octanoate and decanoate) showed an inverse trend which may possibly be ascribed to an increase in the esterification tempo of these kinds of esters at a higher fermentation temperature such as 32°C. The above-mentioned chemical results are reflected in the quality of the respective wines (Fig. 3). In both vintages the judging panel preferred the higher (28°C in 1997 and 32°C in 1998) to the corresponding lower fermentation temperature wines, as the grape-oriented berry/plummy flavours (see 1998 season) were more prominent in the former wines. Although there was no specific evaluation for berry/plummy flavours in 1997, the comments confirmed this statement - despite the fact that the fruity/estery flavours were more prominent in the lower fermentation temperature wines. It is obvious that fermentation temperature can have a dramatic effect on Pinotage wine quality. Consequently one may conclude that, within limits, and probably dependent on factors such as climate, ripeness, etcetera, higher quality Pinotage wines can be made at relatively high fermentation temperatures (28°C to 32°C). |
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