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SASEV Journal abstracts
The following research results, of which the abstracts are provided here, have been published in the South African Journal of Enology and Viticulture. The full text articles are available on the SASEV website www.sasev.org.
Juice and Wine Quality Responses of Vitis vinifera L. cvs. Sauvignon blanc and Chenin blanc to Timing of Irrigation during Berry Ripening in the Coastal Region of South Africa
The effects of additional irrigation during berry ripening on juice and wine quality in Sauvignon blanc and Chenin blanc grapevines were investigated. In all treatments the grapevines were irrigated when berries reached pea size in December. One treatment received no further irrigation until after harvest. All of the remaining treatments received a second irrigation at véraison. Except for a single treatment, which was not irrigated during ripening, these treatments received a third irrigation either 14, 21, 28 or 31 days after véraison. The six treatments were applied in a field trial carried out in the Stellenbosch district of the Coastal winegrowing region of South Africa over consecutive seasons, between 1990 and 1993. Irrigation during berry ripening decreased the N concentration in the juice of both cultivars, but increased the P and Ca concentrations in the juice, though only in Sauvignon blanc. In neither cultivar were the juice K and Mg concentrations affected by irrigation during the ripening period. The irrigation treatments did not affect sugar concentration in Sauvignon blanc grapes. In contrast, sugar concentrations in Chenin blanc grapes that were irrigated 28 days after véraison were lower than in grapes that were irrigated at pea size. Irrigation applied 21 days and 28 days after véraison resulted in higher total titratable acidity in the juice of both cultivars. Irrigation applied 31 days after véraison, i.e. three days before harvest, raised juice pH in Chenin blanc grapes relative to grapevines that received a single irrigation at pea size. Although not consistent over seasons, irrigation applied during the later stages of ripening had negative effects on fresh vegetative aroma (green pepper, herbaceous or green cut grass flavours) and fullness of Sauvignon blanc wines. Similarly, irrigation during the middle stages of ripening reduced the fermentation character (guava flavour) and fullness of Chenin blanc wines, though not in all seasons. Overall, irrigation during berry ripening tended to reduce wine quality in both cultivars.
Effect of Seeding Date on the Performance of Grasses and Broadleaf Species Evaluated for Cover Crop Management in the Breede River Valley Wine Grape Region of South Africa
The trial was conducted over a period of two years on a medium-textured soil near Robertson (33°50’S, 19°54’E), situated in the Breede River Valley of the Western Cape. The effect of seeding date on the dry matter production (DMP) and weed control efficacy of eight grasses and sixteen N-fixing broadleaf species, as well as varieties of three of these species, were determined. The decomposition rate of the surface mulches during summer (from the end of August to the end of January) was measured to determine the persistence of the fibre of the different species. Seeding date had a significant effect on most of the species. Triticale v. Usgen 18 (triticale), Avena sativa L. v. Overberg (‘Overberg’ oats), Avena strigosa L. v. Saia (‘Saia’ oats) and Secale cereale L. v. Henog (rye) effectively suppressed the winter-growing weeds of the region and produced more than the five tons of dry matter per hectare deemed necessary for effective cover crop management with a grass species. These species produced the highest amount of dry matter if sown in early April (mid-autumn). Vicia faba L. v. Fiord (faba bean) and Medicago truncatula v. Paraggio (‘Paraggio’ medic) controlled the winter-growing weeds acceptably, while producing more than the six tons of dry matter per hectare suggested to be necessary for the prevention of erosion in most vineyard soils. Vicia dasycarpa Ten. (grazing vetch) suppressed the winter-growing weeds acceptably. Although these legumes did not produce more than the eight tons of dry matter per hectare deemed necessary for effective control of summer growing weeds under intensive full-surface irrigation, they should still be considered for cover crop management on soils with a low organic matter content in the region, because of their ability to supply nitrogen to the grapevines. A highly significant correlation was found between the decomposition rate of the surface mulch and the initial amount of dry matter present on the soil surface.
The Role and Use of Non-Saccharomyces Yeasts in Wine Production
The contribution by the numerous grape-must-associated non-Saccharomyces yeasts to wine fermentation has been debated extensively. These yeasts, naturally present in all wine fermentations, are metabolically active and their metabolites can impact on wine quality. Although often seen as a source of microbial spoilage, there is substantial contrary evidence pointing to a positive contribution by these yeasts. The role of non-Saccharomyces yeasts in wine fermentation is therefore receiving increasing attention by wine microbiologists in Old and New World wine producing countries. Species that have been investigated for wine production thus far include those from the Candida, Kloeckera, Hanseniaspora, Zygosaccharomyces, Schizosaccharomyces, Torulaspora, Brettanomyces, Saccharomycodes, Pichia and Williopsis genera. In this review the use and role of non-Saccharomyces yeast in wine production is presented and research trends are discussed.
The Influence of Water and Gas Exchange Parameters on Grafted Grapevines Under Conditions of Moisture Stress
Among the four grape varieties that were subjected to moisture stress, Flame Seedless and Thompson Seedless recorded the highest relative water content, osmotic potential and water potential compared to Sharad Seedless and Tas-A-Ganesh. Similarly, Flame Seedless and Thompson Seedless recorded the maximum rate of photosynthesis, the minimum transpiration rate, and thus increased water-use efficiency. Sharad Seedless on its own root had the lowest water-use efficiency. Budding the respective four varieties on different rootstocks and subjecting them to moisture stress resulted in significant differences in various physiological parameters that influence water-use efficiency. When Sharad Seedless was budded on Dog Ridge rootstock and subjected to moisture stress, it resulted in increased water potential, osmotic potential and water use efficiency compared to other rootstocks. This suggests that rootstocks have an influence on the physiological mechanisms of scion leaves. Hence, the genotypic selection of rootstocks for establishing vineyards under drought conditions is of great importance.
Strains of Lactobacillus plantarum in Grape Must are also Present in the Intestinal Tract of Vinegar Flies
Twenty-one lactic acid bacteria isolated from the intestinal tract of Drosophila simulans Stuvervant and nine from Merlot noir grapes were identified as L. plantarum by PCR with species-specific primers and 16S rDNA sequencing. The 30 isolates grouped into four clusters based on RAPD-PCR banding patterns, suggesting that they belong to at least four genotypic groups. Thirteen isolates from grape must and five from the flies yielded identical RAPDPCR banding patterns and grouped into one cluster, suggesting that they are descendants from the same strain. Concluded from these results, L. plantarum (or at least descendants from a specific strain) has the ability to use vinegar flies as a host and vector to infect grape must. Further research is needed to determine the role of this specific strain in wine fermentations.
Effect of Fungicide Spray Cover on Botrytis Cinerea Infection in Grape Bunches
The effect of fungicide spray cover on Botrytis cinerea infection in grape bunches was determined. Bunches were sprayed at pea size and bunch closure with different volumes of a mixture of fenhexamid and a yellow fluorescent pigment, and the percentage fluorescent pigment coverage on pedicels was determined. Bunches were subsequently dusted with dry airborne conidia of B. cinerea in a settling tower and incubated for 24 h at high relative humidity (98%). Infection was determined by estimating the amount of B. cinerea infections on susceptible bunch parts (pedicel, receptacle and rachis) with isolations onto paraquat (herbicide) and Kerssies (B. cinerea selective) mediums. Linear regressions for the part × stage combinations of percentage B. cinerea incidence on different bunch parts were fitted on mean coverage levels. An increase in spray cover caused linear reductions in levels of B. cinerea on bunch parts. Higher B. cinerea incidences were recorded at pea size. Furthermore, higher B. cinerea incidences were found on paraquat medium for both stages, than on Kerssies medium. The information gathered from this study will be used to facilitate future determination of minimum effective coverage levels for effective B. cinerea control in grape bunches.
The Effect of Micro-oxygenation on the Phenolic Composition, Quality and Aerobic Wine-Spoilage Micro organisms of Different South African Red Wines
The effect of micro-oxygenation treatments on the composition of different South African red wines was evaluated. In some wines, micro-oxygenation led to an increase in colour density, with a corresponding change in colour, due to the formation of polymeric pigments. This increase also led to the red colour becoming more resistant to the bleaching effect of SO2. Micro-oxygenation also seemed to be more effective in increasing the colour densities of younger red wines than the older ones, although total red pigments were found to be highest in an older red wine that had received micro-oxygenation. Differences in the gelatine index were also observed over time. The micro-oxygenated and barrel-matured wines also had lower concentrations of catechin and the procyanidin B1, and showed a corresponding increase in polymeric pigment and polymeric phenols. Micro-oxygenation led to higher acetic acid bacteria counts, although no increase in volatile acidity was observed in these wines. A tasting panel preferred younger red wines that had undergone micro-oxygenation. In an older red wine prolonged micro-oxygenation led to the wine becoming over-aged, with an increase in the barnyard/medicinal character, which corresponded with an increase in Brettanomyces counts. Micro-oxygenation can be used to increase the quality of young red wines, but further research is needed in this area.
Shoot Heterogeneity Effects on Shiraz/Richter 99 Grapevines. I. Vegetative Growth
In this study the vegetative growth parameters of normally developed and underdeveloped shoots were compared in an attempt to quantify shoot heterogeneity in a Shiraz/Richter 99 vineyard. A field trial was performed in the Stellenbosch area,Western Cape, South Africa. Comparisons based on certain vegetative growth parameters were made between normally developed and underdeveloped shoots from both shaded and well-exposed canopies. The longer primary shoots of the normally developed shoots matured earlier in the season, with less apparent competition between shoot lignification and grape ripening. Reserves were more evenly distributed in these shoots. Total starch content over the whole shoot was found to be higher in the normally developed shoots, particularly when well exposed. More and longer secondary shoots occurred on the normally developed shoots than on the underdeveloped shoots. No difference was found in the number of primary leaves (leaves on primary shoots) between normally developed and underdeveloped shoots, although the leaf area was much larger in the case of the former. Normally developed shoots had more and larger secondary leaves (leaves on secondary shoots), while all the leaves that developed in the shaded canopies were found to be larger than those in the well-exposed canopies with a higher leaf area:mass ratio. The normally developed shoots seemed to have a greater potential for producing a higher yield, with better quality, than the underdeveloped shoots, as they have a more desirable leaf area composition in addition to a larger total leaf area per shoot.
Oxygen in Must and Wine: A review
Oxygen can play an important role during the winemaking process. It can influence the composition and quality of the must and wine. Phenolic compounds are the main substrates for oxidation in must and wine. Oxygen addition leads to colour changes and the polymerisation of phenolic molecules in wine. Oxygen can, however, also influence the flavour and microbial composition of wine drastically, with certain off-flavours being formed and spoilage micro-organisms able to grow at too high oxygen additions to wine. A state-of-the-art, up-to-date review on the effects of oxygen in must and wine has, however, not been published recently. This review focuses on the effects of oxygen in must, during alcoholic fermentation, extended lees contact and during ageing of white and red wines. The effects it has on acetic acid bacteria and Brettanomyces are also discussed, as well as micro-oxygenation, a relative new technique used in wine production.
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