|
A Technical Guide for Wine Producers
|
|
RECENT ARTICLES | WYNBOER HOME
PINOTAGE RESEARCH
Johann Marais, LRC - Fruit, Vine and Wine Research Institute (Nietvoorbij,
Stellenbosch)
The influence of vine development, foliage density and climate on the
quality of Pinotage
The problem is uncertainty surrounding the issue whether bush vines or trellised vines give the best quality Pinotage. There is also uncertainty about whether Pinotage should be cultivated under cooler or warmer conditions to produce unique wines of exceptionally high quality. The purpose of the project is to investigate the influence of vine development (stem height and cordon orientation) and foliage density (exposure of grapes) on the quality of Pinotage wines under cooler and warmer cultivation conditions in the Western Cape. So far nine experimental locations belonging to eight producers have been identified and will be switched over to the various trellising systems during the coming pruning season. Further negotiations with other producers are currently taking place so that nine more experimental sites required for the project may be obtained. At this early stage in the investigation no experimental results are available and the experimental sites are still being laid out.
The microbiology of red wine fermentation and stuck fermentation.
There is a general tendency among wine makers to ferment their red wines at higher temperatures (even above 30?C) for quicker colour and flavour extraction. It is uncertain whether higher fermentation temperatures alone contributed to the problems with stuck fermentation experienced by various cellars during the 1998 season. Other factors, e.g. nitrogen shortages, pesticide residue, yeast strain selection and higher sugar concentrations also probably contributed to stuck fermentation. Relatively little is known about the interactions between bacteria and yeast cells. With stuck fermentation, generally higher concentrations of certain fatty acids are found. Of these acetic acid is the most common. Acetic acid, even as little as 1 g/l, may inhibit yeast cells, as shown by previous research results. Higher concentrations of other fatty acids, such as hexanoic (C6), octanoic (C8) and decanoic acid (C10), often occur with stuck fermentation. It has been proven that yeasts produce these fatty acids themselves, although it may be toxic for the cells at high concentrations. Decanoic acid starts to inhibit the yeast at 8 mg/L. There is little proof that bacteria may also form these fatty acids. Heterofermentative lactic acid bacteria may increase the levels of volatile acid in wine. Acetic acid bacteria may also cause high levels of acetic acid in must and wine, but to our knowledge it has never been proven that these bacteria are able to form the longer chain fatty acids. Both types of bacteria can inhibit yeasts and thus increase or even cause stuck fermentation and high volatile acid concentrations. With red wine fermentation the temperature in the skin crust sometimes rises as high as 45?C. Readings taken during the past pressing season indicated that the temperatures in the skin crust and the fermenting must can easily differ by as much as 15?C. This may also influence the microbiology of the fermentation. Yeast and bacteria counts during alcoholic fermentation of red wines were undertaken at the University of Stellenbosch and various cellars during the 1998 season. The yeast counts were consistently higher in the skin crust than in the fermenting must. Where fermentation occurred at 15?C, the numbers of lactic acid bacteria were initially lower, but increased again later and reached practically the same levels as at 22?C and 30?C. Where 50 mg/L SO2 was added before fermentation started, the numbers of the lactic acid bacteria were considerably lower during and towards the end of fermentation. In wines prepared without SO2 before fermentation, it was easier for the malolactic acid bacteria to reach the million cells per millilitre usually required for the induction of malolactic fermentation. The acetic acid bacteria numbers were also counted and decreased quicker when SO2 had been used before fermentation. The correct use of SO2, together with a lower pH, can therefore help to control bacteria numbers in the beginning phase of fermentation. Illuminating results were obtained from colour analyses of Pinotage both during fermentation and of the wines seven months after bottling. The colour extraction rate of Pinotage during fermentation is much quicker than that of Cabernet Sauvignon, even with fermentation temperatures as low as 15?C. Wines made with fermentation at 22?C and 30?C showed better colour intensity. Furthermore wines made from preparations where 50 mg/L SO2 was added prior to fermentation, showed better colour intensity than wines made from preparations where no SO2 was used prior to fermentation. Wines that did not undergo malolactic fermentation had much better colour intensity than wines that underwent malolactic fermentation, but this difference may be due to the increased pH. It is important that the pH, especially in Pinotage where much of the acid in the grapes may occur as malic acid, should not be too high prior to malolactic fermentation.
Bitterness in Pinotage - What causes it?
Possible sources of bitterness are the following: phenols are extracted from the skins, stalks and pips of the grapes in the course of processing and during fermentation on the skins. The smaller monomeric phenolic compounds (e.g. gallic acid, catechin, epicatechin) as well as the bigger, condensed phenolic compounds are bitter to a greater or lesser extent. The occurrence of various phenolic compounds may co-operate synergetically to cause bitterness in the wine. Furthermore, it was found that the higher the concentration of alcohol in the wine, the more bitter the wine and that alcohol accentuates the bitter taste of the smaller phenolic components. It is also possible for malolactic bacteria to form acrolein from glycerol during malolactic fermentation. Acrolein in itself is not bitter, but binds with phenolic components in the wine to deliver bitter products. It has not yet been determined what caused the problems with bitterness in Pinotage wines in 1996, but one suspects that it has to do with microbiological activity in the wine in combination with a unique phenolic composition. Further research is being conducted to determine what the problem may have been. Different vinification methods are followed for white and red wines and their influence on the bitterness and phenolic composition of the wines is investigated. The plan is to examine commercial wines which are bitter. With regard to red wine, research includes the influence of microclimate, moisture stress during ripening, fermentation with pips, pre-maceration, SO2 application prior to fermentation, extended skin contact after fermentation, fermentation temperature and malolactic fermentation. With regard to white wines there are investigations into the influence of extended lees contact, skin contact temperature, SO2 dosage during skin contact and pips.
Identification of Pinotage impact aroma components
Intensive investigations have been launched to identify the impact aroma components of Pinotage. Up to now, techniques such as preparative chromatography, gas chromatography, mass spectrometry and sniffing have been used. A further study in Dijon, France, compared Pinotage to Pinot noir. Four impact components were recently identified in Pinot noir, namely two cinnamic acid esters and two anthranilate esters. Only the two cinnamic acid esters occurred in noticeable concentrations in Pinotage wines, while the two anthranilate esters occurred at levels far below those of typical Pinot noir wines. With the sniffing technique, guidelines were obtained which indicate possible components with fruity, berry-like flavours and these tests will now be taken further at Nietvoorbij. Should it be possible to identify the impact components of Pinotage, this knowledge may be used to optimise viticultural and oenological practices and consequently wine quality.
Effect of fermentation temperature on Pinotage wine composition and quality
During the 1997 season, Pinotage wines were made at Simonsig from musts fermented in duplicate at 24?C and 28?C. The 24?C wines had higher concentrations of esters and higher alcohols than the 28?C wines. With regard to quality, the judging panel preferred the 28?C wines to the 24?C, because the grape oriented flavours were more prominent in the former. During the 1998 season the experiment was repeated on Simonsig and musts were fermented in duplicate at 28?C and 32?C. Grapes were harvested at 24?B and WE 14 was used as yeast. Once again the lower fermentation temperature (28?C) caused higher concentrations of acetate esters and higher alcohols than the higher fermentation temperature (32?C). However, contrary to expectations, the ethyl esters (C6, C8 and C10) showed a reverse tendency. With regard to quality, the judging panel once again preferred the higher fermentation temperature (32?C) wines to the 28?C wines, as it displayed more of the typical berry-like Pinotage flavours. It therefore seems that, within limits and probably dependent on numerous factors such as climate, ripeness and so forth, higher quality Pinotage wines are obtained at relatively high fermentation temperatures.
Effect of wood maturation (wood type and time in wood), SO2 levels and
malolactic fermentation on Pinotage wine quality
During the 1997 season a Pinotage wine was made at Kanonkop from grapes harvested at 24?B and fermented with WE14. The wine was matured in nine different kinds of wood, 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. The same wine was treated with two SO2 levels, namely 20 and 80 ppm, and also matured in Vicard Nevers barrels. Malolactic fermentation was tested on the same wine in cement tanks vis à vis wooden barrels and these wines were also further matured in Vicard Nevers barrels. All the wines underwent 12 months' maturation. The control wines in Vicard Nevers wooden barrels were also taken out of the wood at 6 and 9 months to test the effect of time in wood. All tests were done in duplicate. The wines were judged sensorially for Pinotage character (berry/cherry/plum) intensity, wood character intensity and overall wine quality. The effect of malolactic fermentation did not differ between wood and cement. The SO2 (80 ppm) wines showed less fruitiness than the SO2 (20 ppm) wines, but the latter treatment is risky. The 12-month-old wines were higher in quality than the 6 and 9-months-old wines. Subtle differences occurred between the wood types and Vicard Allier produced the highest quality wines. Basically all the wines showed the same fruity flavours (plum, cherry, black currant, banana) and the same wood flavours (coffee, vanilla, smoky, toasted, chocolate, Bovril, tobacco, spicy). Wines differed with regard to the integration of the tannins and wood nuances with the fruity nuances.
Effect of cold skin contact and fermentation on Pinotage wine composition
and quality
Pinotage grapes from Nietvoorbij were used during the 1998 season. The grapes were stored overnight at respectively 10?C and 15?C, and thereafter subjected to skin contact (10?C and 15?C) prior to fermentation for 1, 2 and 4 days respectively. Fermentations were conducted by WE 14 at 25?C. Samples were drawn daily during skin contact and fermentation and analysed for total flavonoids, tannins and anthocyanins. After fermentation the polyphenol levels showed little difference between 10?C and 15?C treatments. The wines were also analysed for esters and higher alcohols. Acetate and ethyl ester concentrations increased with increased skin contact time at 10?C. Skin contact at 15?C showed lower values than at 10?C, especially at 4 days' skin contact time. In general, higher alcohol concentrations increased with increased skin contact time and temperature. With regard to quality, the wines with the highest fruitiness and berry-like intensities, as well as the highest qualities, were those made of musts which underwent 4 days' skin contact at 10?C and 1 day skin contact at 15?C. These are preliminary results and the experiment will be repeated in the 1999 season. It seems, nevertheless, that cold skin contact for specific periods increases Pinotage cultivar authenticity and quality. |
|
Wynboer is incorporated in WineLand, magazine of the SA wine producers.
Visit our sister sites:
|
| UP |
COPYRIGHT (C) 2000 WineLand |