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A Technical Guide for Wine Producers
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The effect of cross-flow filtration - preliminary results
Unfiltered wines as well as wines filtered with bulk filtration and with the Seitz SX04 cross-flow filtration system were supplied by Columbit (Pty) Ltd. The samples included a Pinotage and a Cabernet Sauvignon/Shiraz blend.
Analyses and sensory evaluations
Normal routine analyses and colour measurements according to the method of Iland, Ewart and Sitters (1993) were done. Sensory evaluation was done by a panel of six experienced judges, all winemakers with certificates in wine evaluation. The tastings were done "blind" under scientific conditions in separate booths at the University of Stellenbosch. Limited samples were available for some wines and therefore the complete analyses could not be performed on all wines.
Results and discussion
Table 1 gives the analyses data and Table 2 the wine evaluation data. The results of the colour analyses are illustrated in Figures 1 a-d.
Brief summary of the main effects of the cross-flowfiltration:
Alcohol concentration (Table 1)
The filtered wines had slightly lower alcohol concentrations than the unfiltered samples.
Titratable acidity and pH (Table 1)
The filtered wines had a slightly lower TA than the unfiltered samples. The pH was not affected.
Volatile acidity (Table 1)
The filtered wines had a slightly lower VA than the unfiltered samples.
Extract (Table 1)
The filtered wines had a slightly lower extract than the unfiltered samples.
SO2 concentrations (Table 1)
The filtered wines had a slightly lower total SO2 concentration than the unfiltered samples.
Sensory evaluation data of the wines (
Table 2
)
The cross-flow filtered wines were judged to be more fresh and fruity than the unfiltered wines.
Significant differences were found during ranking of the wines by the panel. The cross-flow filtered wines were preferred for colour, nose and quality (Pinotage) and nose, taste and quality (Cabernet Sauvignon/Shiraz blend).
Colour measurements (Figure 1a-d)
Cross-flow filtered wines were lower in colour density than the unfiltered wines.
Cross-flow filtered wines showed a better (lower) colour hue ie the colour of the wine has a redder shade and less contribution of a negative brown shade.
The total red pigment colour and total phenolics were not affected.
Conclusions
After cross-flow filtration, the wines showed slightly lower alcohol, titratable acidity, extract and colour than the corresponding unfiltered wines, possibly due to the influence of turbidity on the analyses performed rather than actual losses due to filtration. It may be better to compare cross-flow filtration with other types of filtration rather than with unfiltered wines.
The filtered Pinotage was preferred to unfiltered and bulk filtered wine. The judges commented on the more lively colour of the wine and the more characteristic fruity aspect of this wine. For the red blend, the cross-flow filtered wines were judged to be of a significantly better quality than the corresponding unfiltered wines. The judges approved of the fresh characteristics which contributed to the improved wine quality. Colour measurements showed that although the Pinotage cross-filtered wine was less intense in colour than both the filtered and bulk filtered wine, it had the more desired red tint and less brown tint than the unfiltered and bulk filtered wines.
Literature
Iland, P., Ewart, A. & Sitters, J., 1993. Techniques for Chemical Analysis and Stability Tests of Grape Juice and Wine. Partick Iland Wine Promotions.
Acknowledgment
The Department of Viticulture and Oenology, University of Stellenbosch where the analyses and sensory evaluations were done.
Findings at Swartland winery during 2001
In 2000, wine losses of 2,5 - 3 % were recorded during the process of conventional filtration. This year, 0,4 - 0,6 % wine losses were recorded. In 2001, 60% less Kieselguhr was used during bulk filtration than in 2000, when there was no Seitz Crossflow at Swartland. The 2001 Pinotage had more fruity flavours after filtration with the Seitz Microflow, than bulk filtration in 2000. The Seitz Microflow thus had a definite positive influence on the quality of especially Pinotage 2001 wine.
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