By Loftie Ellis of Wine Quality Consultants
The cross-flow filtration experiments were done at the wine cellar of the Elsenburg College of Agriculture in January 2002. Five wines were filtered with the SERET cross-flow system supplied by Envigoration. Samples of the wines were drawn before and after filtration and subjected to analysis. The results of the tests done on the wines are presented in this report.
Cross-flow filtration: SERET cross-flow system. Details of the operating procedures can be obtained from Envigoration, Paarl.
Five red wines were used (Table 1). The wines were not previously filtered and showed high bacterial counts. Some wines showed signs of spoilage such as volatile acidity.
| Cultivar, vintage and description | Volume filtered | Sensory characteristics before filtration |
|---|---|---|
| Pinotage; 2001; unwooded | 4200 L | Medium-intense colour, fruity, no wood, medium full |
| Pinot Noir; 2001; unwooded | 4000 L | Good colour, light VA off-flavour. Wine lacks complexity and freshness. |
| Shiraz; 2000 (ex T4);Barrel aged, before bottling | 1000 L | Good colour, strong wood complexity |
| Shiraz; 2000 (ex T35);Barrel aged, before bottling | 700 L | Good colour, strong wood complexity |
| Cabernet Sauvignon; 2000;Barrel aged, before bottling | 700 L | Good colour, slightly oxidative, still acceptable |
The following analyses were performed by using standard methods (SGS Lab): Alcohol, extract, reducing sugar, VA, TA, pH and SO2. The colour analysis was done by the method of Iland et al., 2000 (Techniques for chemical analysis and quality monitoring during winemaking, Patrick Iland Wine Promotions, Campbelltown). The wines were filtered through a 0.45 micron membrane prior to the colour analysis.
The wines (unfiltered and cross-flow filtered) were ranked by a panel of two expert judges and 19 final year students in Cellar Technology. The evaluation was done two weeks after the treatment. Samples were presented at random with coded numbers and only the cultivar was indicated.
The routine analysis data are shown in Table 2.
| Wine | Treatment | Alc (vol%) | RS | TA | pH | VA | Extract | SO2 F(mg/l) | SO2 T(mg/l) |
|---|---|---|---|---|---|---|---|---|---|
| Pinotage | Unfiltered | 13.23 | 1.60 | 4.95 | 3.79 | 0.38 | 24.2* | 25 | 65 |
| Pinotage | SERET Cross-flow filtered | 13.32 | 1.60 | 4.60 | 3.79 | 0.37 | 31.3 | 20 | 53 |
| Pinot Noir | Unfiltered | 14.38 | 1.50 | 6.66 | 3.81 | 0.69 | 31.5 | 12 | 68 |
| Pinot Noir | SERET Cross-flow filtered | 14.56 | 1.50 | 6.88 | 3.81 | 0.68 | 31.5 | 11 | 69 |
| Shiraz ex T35 | Unfiltered | 14.38 | 1.30 | 6.19 | 3.87 | 0.75 | 32.8 | 14 | 76 |
| Shiraz ex T35 | SERET Cross-flow filtered | 14.11 | 1.30 | 6.14 | 3.86 | 0.75 | 31.8 | 8 | 66 |
| Shiraz ex T4 | Unfiltered | 14.38 | 1.30 | 6.06 | 3.86 | 0.85 | 33.1 | 10 | 68 |
| Shiraz ex T4 | SERET Cross-flow filtered | 13.76 | 1.30 | 5.88 | 3.86 | 0.81 | 31.8 | 8 | 63 |
| Cabernet Sauvignon | Unfiltered | 12.97 | 1.30 | 5.51 | 3.61 | 0.48 | 30.0 | 7 | 117 |
| Cabernet Sauvignon | SERET Cross-flow filtered | 12.19 | 1.40 | 5.48 | 3.61 | 0.48 | 27.9 | 8 | 105 |
Only a brief summary of the main effects of the cross flow filtration will be presented.
| Wine | Treatment | Bacteria levels Cells per ml* | Bacteria type | Comments |
|---|---|---|---|---|
| Pinotage | Unfiltered | >5m | >98% Oenococcus | Too high levels of bacteria. Wine is sensitive to spoilage |
| Pinotage | SERET Cross-flow filtered | <1000 | >98% Oenococcus | Microbiological clean |
| Pinot Noir | Unfiltered | 4 - 6m | 20% Oenococcus80% Lactobacillus | Too high levels of bacteria. Wine is sensitive to spoilage |
| Pinot Noir | SERET Cross-flow filtered | <1000 | 100% Oenococcus | Microbiological clean |
| Shiraz ex T35 | Unfiltered | 1 - 2m | 40% Oenococcus60% Pediococcus | Too high levels of bacteria. Wine is sensitive to spoilage |
| Shiraz ex T35 | SERET Cross-flow filtered | <100 | 100% Oenococcus | Microbiological clean |
| Shiraz ex T4 | Unfiltered | 2 - 3m | 30% Oenococcus70% Pediococcus | Too high levels of bacteria. Wine is sensitive to spoilage |
| Shiraz ex T4 | SERET Cross-flow filtered | <100 | 100% Oenococcus | Microbiological clean |
| Cabernet Sauvignon | Unfiltered | 1 - 2m | >98% Oenococcus | Medium to high levels of bacteria. Wine is sensitive to spoilage |
| Cabernet Sauvignon | SERET Cross-flow filtered | <100 | >98% Oenococcus | Microbiological clean |
The following figures show the effect of the treatment on the total amount of red pigment.
| Treatment | pH | Colour Density | Colour Hue | Total Red Pigment Colour | Deg.of Red Pigment Colour | Total Phenolics | Mod. Wine Colour Density | Mod. Wine Colour Hue | Mod. Deg. of Red Pigment Colour |
|---|---|---|---|---|---|---|---|---|---|
| Pinotage Control | 3.76 | 10.39 | 0.67 | 23.23 | 26.82 | 44.10 | 13.39 | 0.56 | 36.98 |
| Pinotage Filtered | 3.76 | 9.40 | 0.67 | 20.50 | 27.46 | 40.10 | 12.21 | 0.56 | 38.19 |
| Pinot noir Control | 3.77 | 7.48 | 0.84 | 12.42 | 32.76 | 33.60 | 8.10 | 0.76 | 36.95 |
| Pinot noir Filter | 3.78 | 7.07 | 0.84 | 10.71 | 35.96 | 31.60 | 7.67 | 0.76 | 40.63 |
| Shiraz S35 Control | 3.82 | 12.43 | 0.73 | 23.13 | 31.04 | 53.40 | 14.89 | 0.63 | 39.52 |
| Shiraz S35 Filtered | 3.82 | 12.16 | 0.74 | 20.10 | 34.83 | 50.80 | 13.67 | 0.66 | 40.90 |
| Shiraz S4 Control | 3.84 | 12.68 | 0.74 | 20.81 | 34.99 | 53.10 | 14.27 | 0.66 | 41.24 |
| Shiraz S4 Filtered | 3.82 | 11.43 | 0.75 | 19.19 | 34.08 | 48.00 | 12.74 | 0.67 | 39.71 |
| Cab S Control | 3.60 | 15.50 | 0.65 | 18.38 | 51.25 | 59.60 | 16.21 | 0.63 | 54.02 |
| Cab S Filter | 3.59 | 13.97 | 0.66 | 16.36 | 51.52 | 53.80 | 14.48 | 0.65 | 53.78 |
| Wine | Treatment | Rank Totals | Judges comments | Remarks on significance |
|---|---|---|---|---|
| Pinotage | Unfiltered | 28a | Slightly more mouthfeel | No significant differences |
| Pinotage | SERET Cross flow | 32a | Good | |
| Pinot Noir | Unfiltered | 35b | Slightly VA and unfamiliar | Cross-flow filtered wine was preferred by the judges |
| Pinot Noir | SERET Cross flow | 25a | More fresh characteristics, VA? | |
| Shiraz ex T35 | Unfiltered | 28a | Good wooded wine | No significant differences |
| Shiraz ex T35 | SERET Cross flow | 32a | Good wooded wine | |
| Shiraz ex T4 | Unfiltered | Not tasted | ||
| Shiraz ex T4 | SERET Cross flow | Not tasted | ||
| Cabernet Sauvignon | Unfiltered | 27a | Slightly more body | No significant differences |
| Cabernet Sauvignon | SERET Cross flow | 33a | Freshness, more fruit |
The main advantage of the cross-flow filtration process was the removal of almost all bacteria from the wines. All the unfiltered wines showed high bacterial counts and were sensitive to spoilage if exposed to higher temperatures. Cross-flow filtration through 0.22 micron removed almost all the bacteria and thereby eliminated the chance of bacterial spoilage if the wines are to be exposed to higher temperatures.
The minor changes caused by cross-flow filtration in the alcohol concentration, titratable acidity, extract and colour can be ascribed to the fact that these wines were cleaner than the corresponding unfiltered wines when samples were taken for analysis.
No oxidative changes of the wines were experienced from the cross-flow filtration process.
The tasting panel found no significant differences between the unfiltered and the cross-flow filtered wines of Pinotage, Shiraz and Cabernet Sauvignon. The cross-flow filtered Pinot Noir wine was rated significantly better than the unfiltered wine. The unfiltered wine showed unfamiliar characteristics and the filtered wine was judged to be fresher. Both wines showed signs of volatile acidity character.
The SERET cross-flow filtration process was very effective in all five cultivar wines tested in this study.
Envigoration that sells the Seret technology and also operates the machines as a service, can be contacted at (021) 8711877 or on their email address: info@envig.co.za