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A Technical Guide for Wine Producers
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Literature Overview Of Pinotage Research
This literature overview is an abbreviated version of a more comprehensive study available from: SAWIS Industry Library, PO Box 238, Paarl, 7629 - tel (021) 807-5756, fax (021) 872-2354, e-mail library@sawis.co.za.
INTRODUCTION
Pinotage (Pinot noir x Cinsaut), being uniquely South African, is an important red wine cultivar and is currently a sought-after local and export product. Total Pinotage plantings in South Africa increased by 80% between 1997 (3 830 hectares) and 2001 (6 912 hectares) (Anonymous, 2002). Exports increased by 43% between 1997 (5 859 479 L) and 2001 (8 403 479 L). Apart from Chardonnay and Cabernet Sauvignon, Pinotage accounted for the biggest export volumes in 2001. A few years ago Pinotage did not fare so well and wines were produced that displayed overly intense acetone/nail polish flavours. This was caused by various factors, one of the main reasons being that fermentation temperatures were too low. Today Pinotage grapes are picked riper and fermented at temperatures of approximately 28oC to 30oC. Consequently the typical berry, cherry and plum flavours are more prominent.
This literature overview concentrates mainly on published data of scientific as well as a few semi-scientific studies. Popular articles were not taken into account.
VITICULTURE
In the cultivation of grapes the choice of the correct clone is obviously very important. In a comparative study Kriel (1983) evaluated the performance of, inter alia, seven Pinotage clones (on Jacques rootstock) based on crop mass, shoot mass, sugar content, acid concentration, occurrence of viruses and resistance to rot. The most promising clones were subjected to heat treatment to make them virus free, after which they were further evaluated. Pinotage clones that were recommended for the industry, were P4/R50, P3/R4 and P4/R49. Only two clones are widely planted today, namely PI 48 and PI 50, while clone PI 45 is also planted to a lesser extent.
Trellising of wine grape vines and the choice of a trellis system have been a topical subject for many years. A specific trellis system creates a specific microclimate in which grapes are ripened (Archer, 1996). Often the perfect balance is obtained with untrellised bush vines, which is traditionally the case with Pinotage. An extensive investigation of Pinotage is currently being conducted in the Western Cape, to compare trellised and bush vines. Grapes from the selected premises are also being used for another research project which investigates the relationship between grape colour and wine quality.
Irrigation during ripening is an aspect that is of cardinal importance in the determination of berry size, grape composition and wine quality. In the case of Pinotage it was found that in general early irrigation during flowering up to véraison produced an inferior quality wine compared to zero irrigation (Van Zyl, unpublished data). A single irrigation between véraison and ripening consistently produced the best quality wines. Seasonal effects with regard to wine quality were much bigger on unirrigated premises and premises that received little water, than where vineyards were more intensively irrigated. It seems as though irrigation, when judiciously applied, could stabilise wine quality, but dryland vines appear to be more subject to good and bad vintages. The effect of irrigation during ripening on Pinotage composition and wine quality, inter alia, is being further investigated in a current research project.
Concentrations of ammonium compounds in grapes differ among cultivars and are influenced by factors such as climate, soil type, fertilisation and grape ripeness. It is widely known that sufficient nitrogen, such as ammonium, is essential as yeast nutrition for the fermentation process to take its normal course and to prevent the formation of hydrogen sulphide. Ough & Kriel (1985) determined ammonium concentrations in the grapes of nine different cultivars, including Pinotage, in the Stellenbosch area. The ammonium levels ranged from 55 mg/L for Hanepoot to 148 mg/L for Pinotage. Cinsaut and Cabernet Sauvignon also displayed high levels, 107 mg/L and 104 mg/L respectively. The implications of excessive nitrogen levels, namely the effect they have on the formation of the carcinogenic ethyl carbamate, are widely known and practices to bring about lower levels should be adopted [also see OENOLOGY below for a reference to the high nitrogen levels of Pinotage by Joubert (1980)].
OENOLOGY
Optimum ripeness of grapes is an aspect that has been researched for decades, but up to date nobody has found an effective recipe, as a result of the large number of factors that play a role and the complexity thereof. Various parameters which make it easier to reach more accurate conclusions and realise maximum wine quality, were nevertheless identified in the past. Easy ways of measuring ripeness that are still being used, are, for example, sugar content, acid concentration and pH or combinations thereof. Du Plessis & Van Rooyen (1982) determined correlations between these indices and proposed wine quality and optimum ripeness for Pinotage at a sugar content(oB)/total acid concentration ratio of 3.9. This value was calculated using the data of five seasons. In the same context Van Rooyen et al. (1984a; 1984b) also tried to determine an optimum ripeness index for Pinotage using wine analyses and statistical processing of the data. A sugar content (oB) x pH value of between 85 and 95 was proposed.
Today it is widely known that sugar, acid and pH, although important, do not sketch the whole picture and that it is necessary to take into account more factors when determining optimum ripeness, such as, inter alia, physiological, phenolic and aromatic ripeness. Currently a comprehensive research programme, which takes all these factors into account, is being undertaken by Winetech. Obviously Pinotage will also benefit from the results of this investigation.
An earlier study also attempted to identify an objective quality parameter for Pinotage wine by correlating wine composition (namely esters) with wine quality (Marais et al., 1979). By means of multiple regression analyses of the data, hexylacetate and ethyl octanoate were identified as important quality parameters or indicators of quality. This confirms the importance of fermentation bouquet components such as esters in the aroma of young Pinotage wines, as in the case of isoamyl acetate (Van Wyk et al., 1979).
Fermentation bouquet components were also used to distinguish between Pinotage and Cabernet Sauvignon by means of discriminatory analyses, as well as between regions for each of the cultivars (Marais et al., 1981). The intention was to identify components that could possibly be used as quality parameters. Successful classifications were possible using ethyl acetate, isoamyl acetate, ethyl decanoate and hexanol. It is clear that the building blocks of the said components must have differed already between the grapes of the two cultivars, as well as the grapes per cultivar from the respective regions, resulting from the effect of climatic conditions.
The subsequent quest for parameters that are easy to measure and that may be applied to define and predict wine quality, was addressed in a preliminary study on the relationship between Pinotage grape colour and wine quality (Marais et al., 2001). In the light of this specific data, wine quality could be predicted to an accuracy level of 78%. This study indicated that grape colour definitely has the potential to be used as a measure of wine quality for Pinotage and possibly also as a yardstick for producer remuneration according to the quality of the grapes delivered.
One of the most important factors that play a role during vinification is the fermentation process and in particular the temperature during fermentation. In a recent study a fermentation temperature of 24oC produced higher concentrations of esters and higher alcohols than fermentations at 28oC (Marais & Malan, 1999). In a subsequent study the same trend was observed between 28oC and 32oC. In both instances, however, the judging panels preferred the higher fermentation temperature wines to the corresponding lower fermentation temperature wines. The reason being that the grape-oriented, cultivar typical, berry/plummy flavours were more pronounced in the higher fermentation temperature wines. Depending on factors such as climate, ripeness and so forth, a fermentation temperature of approximately 28oC is recommended for the vinification of optimum quality Pinotage wine.
Malan (1996) discussed the characteristics and qualities of Pinotage and recommended the development of different Pinotage wine styles. Investigations were recently launched to develop techniques that would result in maximum quality Pinotage wines. Skin contact temperature and time prior to fermentation and mixing actions during fermentation were investigated, based on phenolic compounds and wine quality. Skin contact prior to fermentation for 2 to 4 days at 10oC produced the highest quality wines, better than the control which had no pre-fermentation skin contact and better than some of the 15oC pre-fermentation treatments (Marais, 2003a; 2003c). With regard to mixing treatments during fermentation, punching down and rotor actions gave higher quality wines than pumping-over actions (Marais, 2003b; 2003d). In both studies higher wine quality went hand in hand with higher flavonoid, tannin and anthocyanin concentrations, as well as more intense berry/plummy aromas.
The identification of cultivar aroma impact components is a very important facet of oenological research. Such components can be applied as quality parameters by undertaking all viticultural and oenological practices with optimum wine quality in mind. In the case of Pinotage isoamyl acetate, which is formed during fermentation, was identified as an important contributing impact component to the typical young wine fermentation bouquet of this cultivar (Van Wyk et al., 1977; 1979). By the addition of this component in various concentrations to non-Pinotage wines, the wines were identified as Pinotage. In moderate concentrations this component is responsible for the characteristic banana aroma, but when it occurs in excessive concentrations, it may display a negative acetone/nail polish type of aroma. In the past Pinotage wines were fermented at temperatures that were too low and this may be regarded as the main reason for the occurrence of this problem, namely excessive isoamyl acetate concentrations. Isoamyl acetate is naturally hydrolised in an acid medium such as wine and it is a simple temperature dependent reaction. The higher the temperature at which wine is stored, the faster the hydrolisation of acetate esters and the quicker the disappearance of the typical banana aroma.
Joubert (1980) undertook an extensive study on the factors that influence the formation of isoamyl acetate. Factors such as soil type, climate, rootstock, time of harvest, sugar, free amino nitrogen, amino acids, trace elements, skin fermentation, free-run, heat treatment (thermovinification) and yeast strain were investigated. The conclusion was that soil type, climate and rootstock probably had no influence on the formation of isoamyl acetate. This is debatable because the concentrations of precursors (amino acids) will definitely be influenced by climatic factors such as temperature and light radiation, which will consequently have an indirect influence on isoamyl acetate levels. Likewise the ripeness at which grapes are picked will have a big influence on the amino acid concentrations, which in turn will influence the acetate composition of the wines. Of the grape composition factors such as sugar, acid, pH, trace elements, macro-elements, phosphates, long chain fatty acids, free amino nitrogen and amino acids, it was found that the latter two definitely influenced the formation of the typical Pinotage fermentation aroma. Furthermore heat treatment of juice had a prominent effect on the increase of isoamyl acetate concentrations. It was also established that the precursors of acetate esters were mostly present in the skins, thus implying that skin contact would also influence isoamyl acetate levels. Yeast strain can definitely have an effect on isoamyl acetate concentration, as has been commonly established in several trials. One gets the impression from the research conducted by Joubert (1980) that treatments resulting in high levels of isoamyl acetate, and therefore by implication more intense Pinotage fermentation aroma, are recommended. In the light of the disadvantages of excessive levels of isoamyl acetate, these treatments should, however, be applied judiciously.
An interesting finding is that free amino nitrogen and amino acid levels of Pinotage musts are higher than those of other cultivars (Joubert, 1980; Ough & Kriel, 1985). Although high nitrogen levels have a positive effect on the formation of the typical Pinotage fermentation aroma, it should not necessarily be seen as an advantage, as it is known to play a role in the formation of the carcinogenic ethyl carbamate. An attempt should instead be made to reduce nitrogen levels, inter alia by not adding too much diammonium phosphate to musts before fermentation.
Joubert (1980) also attempted to ascertain whether other components, in addition to isoamyl acetate, made a contribution to the typical Pinotage fermentation bouquet. Positive correlations were in fact obtained between Pinotage fermentation bouquet and other acetate and ethyl esters, but isoamyl acetate does in fact seem to play the biggest role. This is confirmed by the relatively low threshold value of this component (0.16 mg/L) and the relatively high levels in which it was observed in Pinotage wines (3.73 to 31.55 mg/L)(Joubert, 1980). Ethyl acetate usually also occurs above its threshold value in wine and in low concentrations, it is able to make a positive contribution to wine quality. However, care should be taken with concentrations higher than approximately 50 mg/L, which will then add to the negative volatile acid character. Fact remains that isoamyl acetate, as mentioned above, makes a positive contribution to Pinotage aroma as long as it is limited to relatively low concentrations, which is what happens when the current trend of higher fermentation temperatures is adopted.
Isoamyl acetate is by no means the only aroma impact component of Pinotage. Grape components could possibly also be present that are responsible for the typical Pinotage berry/plum character. Beta-damascenone and beta-ionone are options that are currently being investigated, since these components respectively display prominent fruity/berry and violet aromas and occur in concentrations that far exceed their threshold values in Pinotage wine (Waldner & Marais, 2002).
Wood maturation is an important aspect of red wine vinification and increases the complexity and quality of wine. In an investigation into the effect of various types of wood, as well as time in wood, on Pinotage wine quality, it was found that a minimum of 12 months in new French oak barrels gives the best results with regard to fullness and structure (Marais & Truter, 2000). As regards the type of wood, Vicard Allier and Nadalie Nevers produced some of the highest quality wines.
In a recent study individual polyphenols were determined in a spectrum of South African red wines (Rossouw & Marais, 2003). Big differences in phenolic component concentrations occurred among Pinotage, Cabernet Sauvignon and Shiraz, which may be ascribed to the genetic composition of the cultivars and to climatic differences. So for example Pinotage displayed considerably higher concentrations of malvidin-3-O-glucoside, procyanidin B1 and caftaric acid than the other two cultivars. These are important findings with regard to the authenticity of Pinotage and the role played by these components in wine quality. These aspects are currently being further investigated with the intention of compiling a reliable polyphenol profile for Pinotage.
The role of polyphenols as anti-oxidants in wine and the accompanying health benefits formed the subject of several overseas studies. The evidence shows conclusively that these polyphenols play an important role in the reduction of the occurrence of, inter alia, heart disease. A local study on this topic was recently undertaken by De Beer et al. (2003) who investigated five red cultivars, one of which was Pinotage. With regard to the respective phenolic groups and their ability to remove free radicals, Pinotage did not act any differently to the other red cultivars. This investigation is currently still in progress. The polyphenol/anti-oxidant status of red wines will naturally also depend on the influence of factors such as climate, viticultural and oenological practices.
Current research on Pinotage in the vineyard entails investigations into the effects of irrigation, vine development, canopy density and climate on wine quality. As far as oenology is concerned, the phenol composition, anti-oxidant potential, bitterness, malic acid/tartaric acid ratios and aroma impact components of Pinotage are being researched. In addition wine yeasts are specifically selected for Pinotage and the effect of various vinification techniques on Pinotage wine composition and quality is also being investigated.
CONCLUSION
Various viticultural aspects, such as clone selection, trellis systems, irrigation and ammonium concentrations of the grapes were addressed with reference to Pinotage cultivation. In almost all of these instances Pinotage was part of a spectrum of cultivars that were investigated, and did not act any differently to the other cultivars. The findings are nevertheless applicable to Pinotage cultivation. An exception is the particularly high nitrogen levels found in Pinotage grapes, requiring special attention during vinification.
Oenological studies on Pinotage were more prominent in the past, but it should be borne in mind that some of these investigations were still directed at the old style Pinotage wines. The new style Pinotage wines require a new research approach, which is being adopted in current studies. Oenological aspects that were addressed included how to determine optimum ripeness using sugar, acid and pH and how to optimise the fermentation process, especially with regard to temperature. The role of fermentation bouquet substances, especially isoamyl acetate, and the factors that influence them, have been researched fairly comprehensively. The contribution of other grape-derived aroma impact components, such as beta-damascenone and beta-ionone, was also investigated. The development of vinification techniques that will result in higher quality Pinotage wines has been addressed, especially with regard to pre-fermentation skin contact at low temperatures, mixing treatments during fermentation and wood maturation in oak barrels. The measurement of individual polyphenol concentrations in Pinotage wines and the application thereof to determine authenticity and improve quality, currently receive intensive attention. The importance of polyphenols as anti-oxidants in red wine, with the accompanying health benefits, also forms the subject of a current local study.
It is clear that quite a lot of information about Pinotage exists, but there still remains several lacunae that need to be addressed. Examples are the role of individual phenols in the quality of Pinotage wine, the influence of canopy density on grape and wine composition, optimum ripeness of Pinotage grapes and the selection of wine yeasts specifically for Pinotage. Some of these aspects feature in the research projects that are currently in progress. However, to remain at the forefront of Pinotage research (other countries are already showing interest in this regard), and to promote Pinotage as a uniquely South African cultivar, new initiatives are required to identify and undertake new projects.
LITERATURE REFERENCES
Anonymous., 2002. S.A. Wynbedryfstatistiek Nr. 26. SAWIS. Paarl, Suid-Afrika.
Archer, E., 1996. Oplei van wyndruifwingerde: Verlede, hede, toekoms. Wynboer, April 1996, 55-58.
De Beer, D., Joubert, E., Gelderblom, W. C. A. & Manley, M., 2003. Antioxidant activity of South African red and white cultivar wines: Free radical scavenging. J. Agric. Food Chem. 51, 902-909.
Du Plessis, C. S. & Van Rooyen, P. C., 1982. Grape maturity and wine quality. S. Afr. J. Enol. Vitic. 3, 41-45.
Joubert, W. A., 1980. Faktore wat die vorming van die Pinotage-gistingsgeur beïnvloed. M.Sc.-Tesis, Universiteit van Stellenbosch, Stellenbosch, Suid-Afrika.
Kriel, G. J. le R., 1983. KWV-Plantverbeteringskema. Watter kloon moet ek plant? Wynboer 615, 51-56.
Malan, J., 1996. Pinotage in al sy gedaantes. Wynboer, Januarie 1996, 80-82.
Marais, J., 2003a. Effect of different wine-making techniques on the composition and quality of Pinotage wine. I. Low temperature skin contact prior to fermentation. S. Afr. J. Enol. Vitic. Accepted for publication.
Marais, J., 2003b. Effect of different wine-making techniques on the composition and quality of Pinotage wine. II. Juice/skin mixing practices. S. Afr. J. Enol. Vitic. Accepted for publication.
Marais, J., 2003c. Lae temperatuur dopkontak voor gisting: 'n Tegniek vir die bereiding van hoë kwaliteit Pinotage wyne. Wynboer 166, 13-14.
Marais, J., 2003d. Mengtegnieke van sap en doppe tydens Pinotage wynbereiding. Wynboer 167, 13-14.
Marais, J. & Malan, J., 1999. Effek van gistingstemperatuur op Pinotage wynsamestelling en kwaliteit. Wynboer Tegnies 120, 11-12.
Marais, J. & Truter, B., 2000. Effek van houtveroudering, SO2-vlakke en appelmelksuurgisting op Pinotage wynsamestelling en kwaliteit. Wynboer 129, 7-9.
Marais, J., Iland, P. & Swart, E., 2001. Exploring the relationships between Pinotage grape colour and wine quality - Preliminary results. Wynboer 139, 20-22.
Marais, J., Van Rooyen, P. C. & Du Plessis, C. S., 1979. Objective quality rating of Pinotage wine. Vitis 18, 31-39.
Marais, J., Van Rooyen, P. C. & Du Plessis, C. S., 1981. Differentiation between wines originating from different red wine cultivars and wine regions by the application of stepwise discriminant analysis to gas chromatographic data. S. Afr. J. Enol. Vitic. 2, 19-23.
Ough, C. S. & Kriel, A., 1985. Ammonia concentrations of musts of different grape cultivars and vineyards in the Stellenbosch area. S. Afr. J. Enol. Vitic. 6, 7-11.
Rossouw, M. & Marais, J., 2003. Phenolic compounds in South African red wines: A preliminary study. Wynboer 163, 20-22.
Van Rooyen, P. C., Ellis, L. P. & Du Plessis, C. S., 1984a. Interactions between grape maturity indices and quality for Pinotage and Cabernet Sauvignon wines from four localities. S. Afr. J. Enol. Vitic. 5, 29-34.
Van Rooyen, P. C., Ellis, L. P. & Du Plessis, C. S., 1984b. L'effet du stade de maturité des cépages de raisins sélectionnés sur la composition du jus et du vin. Bulletin de l'O.I.V. 640, 489-501.
Van Wyk, C. J., Augustyn, O. P. H., De Wet, P. & Joubert, W. A., 1977. The role of isoamyl acetate in the typical fermentation bouquet of Vitis vinifera cultivar Pinotage. In: Proc. S. Afr. Soc. Enol. Vitic., 21-22 November 1977, Cape Town, South Africa. pp. 155-171.
Van Wyk, C. J., Augustyn, O. P. H., De Wet, P. & Joubert, W. A., 1979. Isoamyl acetate - A key fermentation volatile of wines of Vitis vinifera cv Pinotage. Am. J. Enol. Vitic. 30, 167-173.
Waldner, M. & Marais, J., 2002. Impact aroma components in South African red wines: A preliminary study. Wynboer 161, 15-17.
Further enquiries may be addressed to: Dr Johann Marais, tel (021) 809-3096, e-mail johannm@infruit.agric.za.
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