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A Technical Guide for Wine Producers
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SASEV 2nd International Congress, 2000
Høj (Australia) sketched the current trends in Australian research. Sufficient funding by a dedicated wine industry makes it possible to intensify marketing, reseach and development strategies. Everyone who has taken note of the Australian research programme over the past few years, will know that they are leaders in many fields. With regard to oenological research their approach is as follows: Positive as well as negative aroma and taste impact components are identified in different cultivars and applied to manage wine styles and quality in the vineyard and cellar. This knowledge is used in an attempt to define and optimise wine quality. The South African goals are quite comparable to those of Australia, but South Africa has to position itself so that research not only emulates that of Australia, but that innovative ideas are created locally. It is important, however, that attention is paid to the strategies they follow.
New technology
Exciting new technology was offered. Versini (Italy) discussed an important aspect, namely the authenticity of wines, musts and distillates. By using nuclear magnetic resonant spectroscopy it is possible to determine by means of isotope analyses (C13/C12 and 18O/16O ratios) whether alcohol derives from another source than grape sugar, and also whether water has been added to wine. With increasing fakes and distribution of grape products all over the world, such control measures are becoming increasingly necessary. The presentation of isotope data showed that it is possible to distinguish successfully between wines from various southern hemisphere countries, namely Chile, Argentina, Bolivia, Uruguay and South Africa. A project on the authenticity of brandy has just been initiated at Nietvoorbij in collaboration with Italy. Crossflow microfiltration was discussed by Stoll (Germany). This advanced filtration technique has certain advantages, such as: no wine losses, lower CO2 losses, prevention of malolactic fermentation, no need for filtration aids, better colour and flavour retention and less labour intensive. A comparison between crossflow and normal filtration under South African conditions resulted in the highest quality wines being produced by the former.
The use of the enzyme, "Lysozyme", was discussed by two researchers, Gerbaux (France) and Petersen (Denmark). This enzyme inhibits the growth of lactic acid bacteria and can therefore be applied to delay or prevent malolactic fermentation. Better control and management of malolactic fermentation is therefore possible. It is important to note that the enzyme cannot replace SO2, but that lower SO2 concentrations are required.
Van Zyl discussed the application possibilities of FT-NIRS ("Fourier Transform Near Infrared Spectroscopy"). Results were presented of free amino nitrogen, sugar content, malolactic fermentation and ethyl carbamate determinations. The degree of accuracy varied, but it is possible to classify and sort data before expensive and time consuming techniques are used to arrive at more accurate determinations. The NIRS technology has definite possibilities regarding the definition of wine quality and is already being used in Australia on a research basis. Other new technology being offered, is a new multipurpose centrifuge (Meckler) and ion exchange as a substitute for traditional acid adjustment (Ellis).
Oenological aspects
To determine the amount of nitrogen required for fermentation to take place successfully, a fast and easy enzymatic technique ("Test Kit") has been developed (Sponholz, Germany). The way it functions was illustrated in the light of various viticultural and oenological treatments.
The role of anti-oxidants in human health is currently a topical subject all over the world. It is generally known that red wine in particular contains high concentrations of anti-oxidants. This was confirmed by the high correlation between phenol content and total anti-oxidant activity (De Beer). A suggestion was made that this anti-oxidant potential of wine may also be used as a parameter of quality. In the same context the anti-oxidant potential of grape waste products (skins, pips, stems) was determined and it was found to increase with increasing phenol content and also that it was higher in red than in white grapes (Joubert, Poster 17). The high anti-oxidant activity of grape waste products opens up new possibilities for extracts thereof to be used as additives to food products.
Marais investigated the effect of cold skin contact prior to fermentation and various mixing actions during fermentation on polyphenol composition and wine quality of Pinotage. It was shown that skin contact at 10°C for 4 days before fermentation, pressing and rotor actions resulted in the highest polyphenol levels, aroma component levels and wine quality. Pinotage is an important cultivar for South Africa and research is necessary to acquire as much knowledge as possible about the cultivar and develop techniques that will produce maximum quality wines. High quality Pinotage wines on international markets may serve as locomotive for other South African red wines.
Just as Pinotage is an important red wine cultivar for South Africa, Sangiovese is significant for Italy and Tannat for Uruguay. Da Dalt (Italy) presented results of Sangiovese cultivation in California. Technology, such as the use of enzymatic complexes and dosage of exogenous tannins, was applied to optimise phenols (anthocyanin-tannin balance) and subsequently enhance wine quality (colour stability and taste harmony). Despite years of experience, research on the polyphenol composition of red wine is still required to optimise red wine making from various cultivars on different terroirs. Carrau (Uruguay) investigated the effect of malolactic fermentation and maturation on Tannat wine composition and quality. Malolactic fermentation resulted in decreases in ester concentrations and berry/fruitiness, as well as increases in inter alia ethyl actate, benzyl alcohol, 2-phenyl ethanol, metionol and diethyl succinate concentrations.
Red wine taste is influenced by tannins extracted from skins and pips. During ripening the structures and concentrations of these tannins change and they are furthermore influenced by interactions with proteins and polysaccharides (Saucier, France). This researcher attempts to use phenolic data to determine phenolic ripeness and therefore optimal harvesting time, which will produce maximum quality wines. This research will possibly shed light on the issue of ripe and green tannins.
When aroma impact components, be they positive or negative, are known, it may be applied to manage quality. Presentations in this regard were those of Rogers who discussed the impact components of Ferdinand de Lesseps (amino-acetophenone = soapy, 2,5-dimethyl-3(2H)-furanone = raspberry) and Kerner (4-vinylguaiacol = elastoplast). Ellis discussed the impact components of matured brandy. This includes sulphur containing components (dimethyl sulphide, dimethyl trisulphide, ethylene sulphide, thiophene) and the pleasant vanillin and octalactones. Although brandies are traditionally made from high quality rebate wines, it was proved that pressing must also produces acceptable quality brandies (Louw, Poster 20). The importance of proper maintenance of used barrels was discussed by Berthelot (France). In addition to the danger of volatile acid development, the presence of bacteria in wine which may penetrate the wood to remain captured there, can result in the formation of negative components, such as ethyl phenols (burnt odour) and trichloro-anisole (musty flavour).
Microbiology
A few papers dealt with the nutritional requirements of yeasts. Different yeast strains require different quantities of nitrogen and oxygen (Dulau, France). Nitrogen (di-ammonium phosphate) and oxygen (micro-oxidation) must be administered with caution for fermentation to occur in full and effectively. The addition of inactive yeast cells, yeast cell walls and mannoproteins to supplement yeast nutrients, was discussed by Rauhut (Germany). In all these cases the development of negative aromas is a risk to be taken into account.
Stuck fermentation remains a world-wide problem. An interesting solution to this problem was suggested by Gafner (Switzerland). According to him, stuck fermentation goes hand in hand with low levels of glucose and high levels of fructose. To complete the fermentation, glucose may be added, but it is illegal and results in the alcohol levels being too high. Therefore it was recommended that Candida stellata yeast, which ferments fructose selectively and will therefore complete the fermentation successfully, be used. Certain strains of this yeast may cause off odours, however, and should therefore not be used.
High levels of acetic acid are associated with stuck fermentation. Bayly (Poster 1) found that various lactic acid bacteria, isolated in the beginning, middle and end of fermentation, produce different amounts of acetic acid. It is therefore important to select bacteria which may form low volatile acid levels, i.e. acetic acid as well as ethyl acetate. High levels of volatile acid also occur in wines that are not subject to stuck fermentation. A research project was initiated at the University of Stellenbosch to investigate the causes of volatile acid production (Lambrechts). Factors such as the effect of non-Saccharomyces yeasts, lactic acid bacteria, degree of ripeness, pH and fermentation temperature on volatile acid production will be investigated in an attempt to solve this centuries old problem.
Various S. cerevisiae yeast strains produce different concentrations of fermentation aroma components (Nicolini, Posters 25 and 26). South African, as well as Italian yeast strains, were tested in fermentations of Italian musts. Yeast strains EC 1118 and N96 produced the highest levels of specific aroma components, as well as wines with the highest fruity/floral flavour intensities. Under the trial conditions yeast strains 9010 INRA Narbonne and Vin13 produced the highest levels of methionol (sulphur-like) which may be ascribed to too low assimilable nitrogen levels of the musts. It is recommended that the fruitiest wines with the highest ester concentrations should mature best, an aspect which also deserves attention locally, with white wines not having a shelf life.
Wild (non-S. cerevisiae) yeast strains occur in different ratios in musts from different areas (Jolly, Poster 16). They may still be present in high concentrations at the beginning of fermentation before pure yeast takes over. Consequently wild yeasts may contribute directly to the aroma composition and quality of wine or they may compete with pure yeast for nutrients and therefore also exert an indirect influence. The positive influence of wild yeasts was illustrated in the light of the results (Jolly).
Other microbiological aspects that were touched on, included the genetic stability of commercial yeast strains (Grossmann, Germany), the role of yeast strain in the production of glycerol (Nieuwoudt, Poster 27), the ability of commercial yeast strains to produce ureum (the precursor of the carcinogenic ethyl carbamate) from arginine (Farmer, Poster 11) and the determination of optimum fermentation conditions for the production of marula wines and distillates (Fundira, Poster 12).
Biotechnology
A considerable amount of work on the genetic manipulation of yeasts has already been done at the Institute for Biotechnology in Stellenbosch. Examples are the following: A successful malolactic fermentation is often unpredictable. As an alternative Volschenk transferred the genes of Schizosaccharomyces pombe, which enables this yeast to degrade malic acid to ethanol and CO2, to commercial S. cerevisiae yeast strains. By so doing the commercial yeast strains acquired the same capacity for transformation of malic acid and it is claimed that quality wines may be produced from these manipulated yeasts.
Certain volatile phenols, such as the 4-vinyl and 4-ethyl derivatives, are important contributors to the aroma quality of certain white as well as red wines, and may be detrimental to wine quality if the concentrations are too high. By using genetic manipulation of S. cerevisiae yeast strains, an attempt will be made to control the formation of these phenols from phenolic acids and thus improve wine quality (Maritz, Poster 22). Throughout the world research is being done to reduce SO2 applications or to replace SO2 altogether as a preservative. Natural biopreservatives, such as bacteriocins (anti-microbial, protein-like compounds), which are produced by lactic acid bacteria for example, appear to be a natural alternative to SO2 and are therefore paid more and more attention. D’Aguanno (Poster 9) succeeded in transferring the specific genes of bacteria, that produce these compounds, to S. cerevisiae yeast strains and illustrated that the modified yeast is able to fulfil this function successfully. Bauer used genetic manipulation to reconstruct certain genes of S. cerevisiae to improve the flocculation ability of this yeast.
Pretorius gave an overview and future view of genetically manipulated yeasts. The philosophy to modify commercial yeast strains so that they may function optimally and comply with the wine industry’s increasing demands for specialised wine yeasts, was once again emphasised. Mention was also made, however, of opposition by consumer groups world-wide to genetically manipulated plants and microbes. At the moment such yeasts may not be released locally. Some of the specific fears and questions being asked, include: "Will genetically manipulated yeasts spread to such an extent in nature that they will oust the natural microbes?" To allay these fears, a study was launched to determine the extent to which commercial yeasts are able to spread in the vicinity of cellars and influence future fermentations in the cellar (Muller, Poster 24). The hypothesis was obviously that manipulated yeasts would follow the same distribution patterns than commercial yeasts. Results differed from region to region and locality to locality Vin13 and N96 did occur in vineyards, however. The conclusion was reached that taking into account the large number of yeast isolates, it seems as though commercial yeasts will not spread easily from the cellar.
Environmentally friendly wine production
Grape and wine production, like other industries, put enormous pressure on natural resources such as water and soil. Over the past few years the "clean and green environment" philosophy has also already found a firm foothold in the South African wine industry. Hayward discussed aspects of an environmental management system for the wine industry. An amended version of ISO 14001 as an environmental management system for the local industry is currently being investigated (Egypt). Parallel to this is the development of the IPW (Integrated Production of Wine) system, which guarantees environmentally friendly vinification. This system is already being applied successfully in South Africa (Tromp).
In support of these systems research is being done to accomplish the treatment of cellar waste-water, the removal of chemicals from it, the reduction of the COD (Chemical Oxygen Demand) thereof and the general improvement of the quality of waste-water. Examples are the biological treatment of cellar waste-water (Viljoen-Bloom), where the COD has been successfully reduced by means of yeast isolates, the DAF (Dissolved Air Flotation) technology at Fredericksburg to remove low density particles from cellar waste-water (Koch) and the ABR (Anaerobic buffle reactor) to remove biodegradable organic material (Dekker).
Conclusion
A wide variety of topics was covered and about half the papers were presented by foreign delegates from Australia, Denmark, Germany, France, Italy, Switzerland and Uruguay. With regard to the theme of the congress, the following oenological topics stand out as current trends in the new world wine countries:
Summaries of the papers and posters may be obtained from SASEV at the following address:
South African Society for Enology and Viticulture,
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The theme of the 2nd SASEV International Congress, held in Cape Town from 8 to 10 November 2000, was: "Trends in quality wine production in the new world". This overview will attempt to answer the following questions, namely: Did the content of the oenological and related papers and posters comply with the theme? Is the South African wine industry on track as far as oenological research is concerned?
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