INTRODUCTION

As a result of its uniqueness to this country and the heightened awareness of this cultivar over the past few years, Pinotage is becoming more and more significant to South Africa. The Pinotage Association was founded to serve the interests of Pinotage. Apart from the efforts made by certain dedicated producers, research is also undertaken to support the Pinotage initiatives and develop techniques for the production of higher quality Pinotage wines.

Wood ageing is an important aspect of red wine making and increases the complexity and quality of wine. During this process various factors play a role, for example malolactic fermentation (MLF) and SO2 application. There is little knowledge about the effect of the above-mentioned factors on the quality of Pinotage wine. Therefore the effect of wood-ageing (wood type and time in wood), MLF in cement tanks versus MLF in wooden barrels and differing total SO2 levels (20 and 80 ppm) on Pinotage wine composition and quality was investigated.

MATERIAL AND METHODS

The trial was conducted on commercial scale in duplicate at Kanonkop during the 1997 season. Grapes were harvested at 24B, crushed and fermented in open fermenters. A total SO2 level of 60 ppm was maintained. The crushed grapes were continuously (6 to 8 times in 24 hours) punched down in open fermenters. The fermentation took place with WE 14 between 28C and 32C. After three to four days’ fermentation (to approximately 5B) the skins were pressed, the juice racked and further fermented dry in epoxy-coated cement tanks. Then MLF was conducted with Viniflore oenos in cement tanks and the wines handled further according to standard cellar practices.

The wines were aged in nine different types of wood (barrels of different types of wood as well as the same type of wood from different coopers) for 12 months, namely Vicard Nevers (control), Vicard Allier, Vicard Troncais, Vicard Frans, Sylvain Nevers, Nadalie Nevers, Demptos Nevers, Sequin Moreau Nevers Export and Sequin Moreau Nevers Chateaux. In addition to the above-mentioned treatments the same wine was also made with two total SO2 levels of 20 and 80 ppm and also aged in Vicard Nevers barrels. Malolactic fermentation on the same wine was investigated in cement tanks versus wooden barrels and these wines were also further aged in Vicard Nevers barrels. The control wines in Vicard Nevers barrels were also sampled at 6 and 9 months, in addition to 12 months’ ageing, to investigate the effect of time in wood. The first two treatments were immediately bottled and stored at 15C until the 12 month wood aged wines were ready. All the other wines were bottled after 12 months in wood.

After wood ageing (i.e., one year after the harvest) the wines were evaluated sensorially for Pinotage character (plum/berry/cherry) intensity, wood character intensity and overall wine quality by an experienced panel of six judges. After one year’s storage in the bottle at 15C (i.e., two years after the harvest) the wines were again judged sensorially by five judges. In this second instance rankings were done to distinguish between the effects of MLF in cement and wood, between 20 ppm and 80 ppm total SO2 levels and between 6, 9 and 12 months wood ageing. With regard to the different wood types, the panel was only asked to select the three wines with the highest quality. In addition to the sensory evaluation the wines were also analysed spectrophotometrically for total flavonoids, tannins and anthocyanins after one year in the bottle.

RESULTS AND DISCUSSION

Chemical data

The total polyphenol (flavonoids, tannins and anthocyanins) concentrations are given in Figures 1 and 2. No noteworthy differences were found between MLF in cement and MLF in wood, nor between SO2 levels of 80 ppm SO2 and 20 ppm SO2. Time in wood resulted in a slight decrease in total flavonoid, tannin and anthocyanin concentrations. Hardly any differences occurred between the different wood types, with Vicard Frans as a possible exception (Fig. 2).

Sensory data

No noteworthy differences in quality between MLF in cement and MLF in wood were found. This is true for judging both in 1998 and 1999 (Fig. 3; and Table 1) and therefore agrees with the slight differences in total polyphenol concentrations between the two treatments (Fig. 1). There were comments, however, that MLF in wood caused a slight bitterness.

Table 1. Rankings of Pinotage wines according to wine characteristics and overall wine quality.

Treatment Wine characteristic/Ranking

Treatment Wine characteristic/Ranking
Plum/ berry/ cherry
(Intensity)
Wood character
(Intensity)
Overall wine quality
MLF in cement 16 16 14
MLF in wood 14 14 16
20 ppm total SO2 18 17 17
80 ppm total SO2 12 13 13
6 months in wood 18 26 21
9 months in wood 22 18 22
12 months in wood 20 16 17

Each value represents the total of the placings of the judges (Duplicate treatments). The lowest value = strongest intensity or highest quality; Highest value = weakest intensity or lowest quality. Judging of wines occurred after two years’ ageing (1 year in wood followed by 1 year in bottle). All wines were matured in Vicard Nevers barrels.

At the 1998 judging the 20 ppm SO2 wines showed less wood character than the 80 ppm SO2 wines (Fig. 3), probably because they were masked by a more intense fermentation bouquet. At the 1999 judging, the 80 ppm SO2 wines were preferred to the 20 ppm SO2 wines in all instances, namely with regard to plum/berry/cherry character, wood character and overall wine quality (Table 1). The main reason for this was the occurrence of bitterness at the lower SO2 levels, which can probably be ascribed to bacteriological actions. It is known, for example, that acrolein is formed by bacteria and that this component combined with certain phenols causes bitterness.

With regard to time in wood, it appears that the plum/berry/cherry character was slightly more prominent in the 6 months than in the 9 and 12 months wood aged wines, which may be explained by the masking effect of the more intense wood nuances in the latter two treatments (Fig. 3; Table 1). With regard to total wine quality the 12 months”wines were better than the 6 and 9 months ageing, because the typical Pinotage and wood characters were more complex and integrated. This increase in complexity may be ascribed, inter alia, to an increase in concentration of other phenolic or wood components, such as oak lactones.

At the 1998 judging differences in wine quality occurred between the wood types and Vicard Allier showed the best potential (Fig. 4). To a large extent this was confirmed at the 1999 judgings, when the wines with the highest quality were selected, namely that Vicard Allier, as well as Nadalie Nevers, were judged to be the two best types of wood (Table 2). In general all the wines displayed the same fruity flavours (plum, cherry, blackberry, banana) and the same woody flavours (coffee, vanilla, smokey, chocolate, bovril, tobacco, spices). Consequently differences may be ascribed mainly to the integration of the tannins and wood nuances with the fruity nuances, specifically at the 1998 judging. In the light of the above it is relatively difficult to choose between the wood types, since all of them produced relatively high quality wines.

In general it may be said that the relationship between the specific chemical and sensory data is difficult to explain and further investigations are necessary, especially with regard to individual volatile and non-volatile phenols.

Table 2. Preferences for type of wood according to total wine quality.

Type of wood Number of instances selected
Vicard Nevers (control) * *
Vicard Allier * * * * *
Vicard Troncais * * *
Vicard Frans * *
Sylvain Nevers * * * *
* * * * *
Demptos Nevers * * * *
Sequin Moreau Export * * * *
Sequin Moreau Chateaux *

Selected by a judge (Duplicate treatments judged separately). Each judge could select three wines. Judging of wines occurred after two years’ maturation (1 year in wood followed by 1 year in bottle).

RECOMMENDATIONS

It is recommended that if Pinotage wines are to be aged in wood, this should occur in new French oak barrels for at least 12 months to obtain wines with more body and structure. It appears as though Vicard Allier and Nadalie Nevers produced higher quality wines under the conditions of this specific investigation. At present a more comprehensive wood ageing trial, which includes apart from French also American and Russian oak, is being conducted by the Oenology Department of the University of Stellenbosch. It is very important to maintain sufficient SO2 levels (60 ppm) to prevent possible detrimental bacteriological effects. The periodic occurrence of bitterness in Pinotage may possibly be ascribed to, inter alia, SO2 levels that are too low. This aspect is currently being investigated in a project at Nietvoorbij.

Other vinification aspects that should be investigated is the effect of punching-down frequency on Pinotage composition and quality. The punching-down action in red wine vinification is a critical step in the extraction of phenolic and aroma components and should be optimised, since this involves many man hours (in conventional punching-down) and various techniques.

ACKNOWLEDGEMENTS

The technical assistance of Ewarda Swart is much appreciated.

The Authors:

Johann Marais1) & Beyers Truter2)
1)ARC Infruitec-Nietvoorbij, Stellenbosch
2)Kanonkop Estate, Stellenbosch

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