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A Technical Guide for Wine Producers
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Techniques for mixing juice and skins during pinotage wine production
Key words: Pinotage wine, punching-down, pumping-over, rotor
INTRODUCTION
In recent years Pinotage has undergone a renaissance and currently it is a sought-after domestic and export product. Research on Pinotage is an important goal of the Pinotage Association as well as the wine industry and focusses, inter alia, on the development of oenological technology that will result in optimal wine quality.
During fermentation, numerous aromatic and taste components and colourants are extracted from the skins, which have a huge influence on wine quality. The purpose of this investigation was to determine the effect of various mixing techniques on the composition and quality of Pinotage wine.
MATERIAL AND METHODS
Pinotage grapes from three seasons (2000 to 2002) from the Nietvoorbij farm were used in the investigation. The grapes were harvested at between 23°B and 24°B, stored overnight at 15°C and crushed the following day. The crushed grapes were inoculated with Saccharomyces cerevisiae yeast strain WE 14 and fermented dry at 25°C. During fermentation three mixing techniques were used, namely punching-down with a wooden punch, pumping-over (imitated by racking the wine into a bucket and pouring it over the skins) and the rotor action (imitated by putting the juice/skin mixture in drums and rolling them once to and fro over a distance of 5m). Each mixing action took place hourly and three-hourly, respectively, between 07:00 and 19:00 until fermentation was completed. The control was the hourly punching-down treatment. The entire trial was conducted in triplicate. Further wine making actions took place in accordance with standard Nietvoorbij small scale wine making practices.
The wines were analysed for esters, higher alcohols, total flavonoids, total tannins and total anthocyanins, as well as evaluated sensorially for the characteristic Pinotage berry/plum aroma intensity and overall wine quality.
RESULTS AND DISCUSSION
Previously, when Pinotage was fermented at temperatures that were too low, esters such as iso-amyl acetate occurred in excessively high concentrations and consequently displayed an acetone/nail polish type of aroma. Currently Pinotage, just like other red cultivars, is fermented at relatively high temperatures, resulting in lower iso-amyl acetate concentrations. At these levels a positive, banana-like aroma is manifested. In this investigation the rotor action produced higher acetate ester concentrations than the other two treatments, but the levels could still be considered positive (Table 1).
The highest polyphenol concentrations were observed with the punching-down and rotor treatments, while the pumping-over treatment consistently gave the lowest values (Table 1). This phenomenon could be ascribed to the fact that pumping-over is a gentler action with more oxygen contact, probably resulting in polymerisation and precipitation of certain phenolic components.
With regard to wine quality, the highest berry/plum intensities and overall wine qualities occurred consistently with the punching-down and rotor treatments and the lowest with the pumping-over treatments (Table 1). To a large extent this agrees with the polyphenol concentration pattern.
In general no significant differences in acetate ester concentrations, polyphenol concentrations and wine quality were observed between 1 and 3 hourly treatments (Table 2).
CONCLUSIONS AND RECOMMENDATIONS
Mixing techniques of crushed grapes during fermentation have a significant effect on Pinotage composition and wine quality. Under the conditions of this trial, the punching-down and rotor actions produced the most typical and highest quality Pinotage wines. These techniques are therefore recommended. Pumping-over could also be a suitable technique, however, since it produces wines with a softer structure. The choice of mixing technique or combinations of techiques will be determined by, inter alia, the ripeness of the grapes. It is therefore important for individual cellars to consider these techniques before applying any specific one. Differences in wine quality between 1 and 3 hourly treatments were not significant under the conditions of this trial. This finding is important with regard to the financial implications when additional manpower and electricity come into play with increased frequency of treatment.
ACKNOWLEDGEMENTS
Financial support for the investigation from Winetech, the Pinotage Association and the ARC, as well as the input from Ewarda Swart, Francois October, Adéle Louw and Christopher Paulse, are much appreciated.
Further queries may be addressed to: Dr. Johann Marais (Tel: 021 809 3096; e-mail: johannm@infruit.agric.za)
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Dr. J. Marais - ARC Infruitec-Nietvoorbij, Stellenbosch.
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