South African Journal of Enology and Viticulture

High alcohol wines have become a major challenge in the international wine trade. Several physical processes are used to produce wines with reduced-alcohol content, all of which involve the selective extraction of ethanol based on volatility or diffusion. In this study, the possibility of Gluzyme Mono® 10.000 BG (Gluzyme) (Novozymes, South Africa) to reduce the glucose content of synthetic grape juice before fermentation was investigated in order to produce wine with reduced-alcohol content. Gluzyme is a glucose oxidase preparation from Aspergillus oryzae, currently used in the baking industry. Glucose oxidase catalyses the oxidation of glucose to gluconic acid and hydrogen peroxide(H2O2) in the presence of molecular oxygen. Gluzyme was initially used in synthetic grape juice, where different enzyme concentrations and factors influencing its efficiency were investigated under winemaking conditions. The results showed up to 0.5% v/v less alcohol at an enzyme concentration of 20 kU compared to the control samples. This reduction in alcohol was increased to 1 and 1.3% v/v alcohol at pH 3.5 and pH 5.5 respectively in aerated (8 mg/L O2) synthetic grape juice using 30 kU enzyme. Secondly, Gluzyme was used to treat Pinotage grape must before fermentation. Gluzyme-treated wines at 30 kU enzyme concentration after fermentation contained 0.68% v/v less alcohol than the control wines. A decrease in acetic acid concentration of the treated compared to control wines was also observed.

In this study, the physiology of normally developed and underdeveloped shoots is compared in an attempt to quantify the effect of shoot heterogeneity in a Shiraz/Richter 99 vineyard, located in the Stellenbosch area of the Western Cape, South Africa. Comparisons are made between normally developed and underdeveloped shoots from shaded and well-exposed canopies. In the first five weeks after véraison, photosynthetic and transpiration rates, stomatal conductance and water-use efficiency (WUE) decreased as berry ripening progressed, while the internal CO2 levels of the leaves increased. Since differences in activity between individual leaves from normally developed and underdeveloped shoots only became apparent in the third week after véraison, it seemed as if the leaf area per shoot played a more important role than the photosynthetic output per unit leaf area in determining photosynthetate supply to the rest of the vine up to this stage. From the third week after véraison, higher levels of photosynthetates were produced by normally developed shoots than by underdeveloped shoots, due to the larger effective leaf area per shoot as well as the higher photosynthetic activity per unit leaf area. This points to premature senescence of the leaves on underdeveloped shoots. The quantity and quality of the yield from normally developed shoots are expected to benefit from the higher physiological output of the leaves. The enhancing effect on leaf functioning induced by canopy exposure became apparent from the third week after véraison.

In this study, the leaf chlorophyll content of normally developed and underdeveloped shoots was compared in an attempt to quantify the effect of shoot heterogeneity in a Shiraz/Richter 99 vineyard, located in the Stellenbosch area of the Western Cape, South Africa. Comparisons are also made between normally developed and underdeveloped shoots from shaded and well-exposed canopies. No positive correlation was found between the photosynthetic activity and the chlorophyll concentration of the leaves at five weeks after véraison. Equal amounts of chlorophyll per cm2 and a non-significant difference in the assimilation rate were calculated for the leaves of normally developed and underdeveloped shoots. No significant differences were found between the shaded and well-exposed canopies. It therefore appears that it is the effective surface area per leaf or per shoot rather than the chlorophyll concentration or activity that may be responsible for any apparent difference in the photosynthetic output of the leaves from normally developed and underdeveloped shoots in shaded or well-exposed canopies.

There are two main fermentations associated with the winemaking process. Alcoholic fermentation is conducted by the yeast culture and malolactic fermentation takes place as a result of the metabolic activity of lactic acid bacteria, specifically from the genera Oenococcus, Lactobacillus, Pediococcus and Leuconostoc. Malolactic fermentation is dened as the conversion of malic acid to lactic acid and CO2 and besides deacidification also contributes to microbial stability and modification of the aroma prole. This paper aims to provide a comprehensive review discussing all the main aspects and factors related to malolactic fermentation, including practical considerations for monitoring and ensuring a successful fermentation.

The volatile composition of 925 single cultivar young Sauvignon blanc, Chardonnay, Pinotage, Merlot, Shiraz and Cabernet Sauvignon wines of vintages 2005 to 2007, was determined using gas chromatography-flame ionisation detection. Compositional data were compared to published data on young wines from South Africa and other countries. South African young wines analysed in this study had a largely similar volatile composition to that reported in the literature. Significant between-vintage and between-cultivar differences were observed in the volatile composition of the wines investigated in this study. The concentration ranges of four compounds in red wines, hexanol, propanol, diethyl succinate and ethyl lactate, and four compounds in white wines, 2-phenylethanol, hexanoic acid, isoamyl acetate and propanol, were not influenced by vintage effects. This finding was interpreted as the first indication that typical concentration ranges for some aroma compounds can be established for South African young cultivar wines. A trend was observed in the white wines that the alcohols and their respective acetate esters, as well as fatty acids and their ethyl esters, were responsible for the vintage-related effects. Differences in volatile composition between Chardonnay and Sauvignon blanc wines could also largely be explained on the same basis. Classification models were established to discriminate between individual red wine cultivars and between the two white wine cultivars and correct classification rates of respectively, 79 % and 85 % were achieved.

This study was conducted as part of a larger investigation into the effect of management practices on selected sown cover crops and the effects thereof on grapevine performance. The aim of this study was to determine the effect of these cover crops on plant parasitic nematode populations under natural field conditions. The trial site was in an own-rooted Sultanina vineyard situated in the Lower Orange River of the Northern Cape Province. Three management practices were applied selectively to ten cover crop species, with two control treatments consisting of weeds. Nematodes were monitored for a period of four years. 'Saia' oats were indicated as being poor hosts to both root-knot and root-lesion nematodes, while 'Overberg' oats showed poor host status against ring nematodes. 'Midmar' ryegrass and 'Paraggio' medic were also poor hosts for root-knot nematodes, while grazing vetch appeared to be a good host for root-knot nematodes. The most notable result from this study was the relatively high numbers of all three nematodes on the vine row, as opposed to the inter-row where cover crops were established. This indicates that vines were much better hosts for these nematodes than the cover crops. It is recommended that if more definite trends are to be observed, Brassica species, which have direct toxic/repellant effects on nematodes, should be tested.

The purpose of this study was to investigate the use of different wood types and treatments, and extraction media to induce rapid ageing of brandy. Extracts were prepared from American and French oak, specially prepared and supplied by a cooper, and from commercially obtained oak; both representative of different toasting levels, including untoasted, light, medium and heavy toasted. To extract the wood components, wood chips in either 55% (v/v) neutral wine spirits or water media were boiled under reflux. Distillation was followed by either open (higher boiling temperature) or closed (vacuum or reduced pressure - lower boiling temperature) concentration of the decanted solvent by 45, 65 and 85% (v/v). The concentrated extracts were fortified. Screened extracts were added to unmatured pot-still brandy and aged for eight months at room temperature in glass containers. Controls were stored below 0°C. Matured and unmatured (control) pot-still brandy samples were analyzed for wood-derived congeners by means of HPLC and GC. This article focuses on the effects of the extraction media, and on level and method of concentration (open and reduced pressure) on sensory quality and chemical composition. The treatments that gave acceptable extracts, and the best overall quality pot-still brandy were those that entailed (1) using ethanol instead of water as extraction medium, and (2) levels of concentration above 45% (v/v). Open and reduced-pressure concentrations showed little difference in the quality of the products yielded. Treatments yielding the most acceptable extracts and best overall quality pot-still brandy generally also contained higher concentrations of volatile and less volatile wood-derived congeners. Multivariate data analysis was conducted on the pot-still brandy samples representing the different treatments. Discriminate analysis provided better separation of samples than principal component analysis.

As part of a broader study that investigated techniques for the rapid induction of the needed ageing character in brandy products, the effect of oak type on quality and chemical composition of oak wood extracts and matured and unmatured potstill brandy, is reported on. Extracts, prepared from American and French oak chips supplied by a South African cooper, and from commercially obtained oak, and representing different levels of toasting, were added to 70% (v/v) unmatured pot-still brandy and stored for eight months in glass containers (Schott bottles) at room temperature, or in the case of controls, below 0°C. Matured and unmatured (control) pot-still brandy samples were analysed for wood-derived congeners by means of HPLC and GC. Although French oak initially yielded better quality products, these effects lost prominence and, after eight months maturation, yielded similar sensory quality to American oak. French oak samples had higher concentrations of wood-derived congeners (including eugenol, the furan derivatives and aromatic aldehydes). However, the American oak generally contained higher concentrations of oak lactones than their French counterparts, with higher proportions of the more sensorially potent cis-form of lactone than its trans-isomer.

As part of a broader study that investigated techniques for the rapid induction of the needed ageing character in brandy products, the effect of oak wood toasting on quality and chemical composition of oak wood extracts and matured and unmatured pot-still brandy, is reported on. Extracts, prepared from oak chips supplied by a South African cooper, and from commercially obtained oak, and representing different oak types and levels of toasting (i.e. untoasted, light, medium and heavy), were added to 70% (v/v) unmatured pot-still brandy and stored for eight months in glass containers (Schott bottles) at room temperature, or in the case of controls, below 0°C. Matured and unmatured (control) pot-still brandy samples were analysed for wood-derived congeners by means of HPLC and GC. Toasted, as opposed to untoasted oak, gave acceptable extracts, the best overall quality pot-still brandies and generally higher concentrations of volatile (GC-determined) and less volatile (HPLC-determined) wood-derived congeners. Toasting provoked an important separation as indicated by discriminant analysis.

The presence of biogenic amines in wine is becoming increasingly important to consumers and producers alike, due to the potential threats of toxicity to humans and consequent trade implications. In the scientific field, biogenic amines have the potential to be applied as indicators of food spoilage and/or authenticity. Biogenic amines can be formed from their respective amino acid precursors by various microorganisms present in the wine, at any stage of production, ageing or storage. To understand the large number of factors that could influence the formation of biogenic amines, the chemical, biochemical, enzymatic and genetic properties relating to these compounds have to be considered. Analytical and molecular methods to detect biogenic amines in wine, as well as possibilities that could enable better control over their production levels in wine will also be explored in this review.

Anagyrus species near pseudococci (Girault) and Coccidoxenoides perminutus (Timberlake) (Hymenoptera: Encyrtidae) are well-known mealybug parasitoids. Both are proven biological control agents of Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae) in vineyards. These parasitoids are affected by some pesticides used for the control of ants (Hymenoptera: Formicidae) and P. ficus in vineyards. To establish which of the vineyard pesticides is more toxic to parasitoids, pesticide bioassays were carried in the laboratory using adult and pupal parasitoids. Fipronil and α-cypermethrin caused significant acute toxicity of both parasitoids. Low mortality was recorded for all these pesticides for parasitoids emerging from mummies indicating that the mummy case was an effective barrier to pesticides for parasitoids. Buprofezin, mancozeb and an insecticidal soap were not toxic to parasitoids in both bioassays. Some pesticides have far-reaching negative impacts on parasitoids of orchard and vineyard arthropod pests. A refinement on pest management strategies regarding method and timing of application of pesticides where parasitoids constitute part of the pest management program is essential.

The Vitis vinifera cultivar Crimson Seedless primarily accumulates the anthocyanin peonidin-3-glucoside. The research undertook the study of two factors which could influence the accumulation of anthocyanin in grape berry skins: ethephon application and shade. Ethephon treatment at 200ppm applied one week post-véraison significantly increased the concentration of all anthocyanins in berry skins. Peonidin-3-glucoside was found to increase most significantly in response to ethephon application, and was increased 150% compared with an untreated control. The proportion of 3-monoglucoside anthocyanins increased in response to ethephon application. A shading treatment did not affect total anthocyanin concentration in berry skins, but the anthocyanin cyanidin-3-glucoside was decreased significantly by shade. Its content was 50% of a sun-exposed control. The observed effects were found to occur at two sites at which the experiment was performed in the Hex River and Paarl regions. Colour development in the Vitis vinifera cultivar Crimson Seedless does not appear to be influenced significantly by bunch shading. The use of commercial growth regulators like ethephon exert a strong influence on anthocyanin production in grape skins of this cultivar, and are therefore a more likely solution to overcome poor colour development in its production.

The effect of oxygenation on the phenolic composition, total antioxidant capacity (TAC), colour and sensory quality was investigated during the maturation of Pinotage wines. Oxygenation was carried out in discrete monthly doses at two oxygen dosages (2.5 and 5.0 mg O2/L/month) for zero, two, four and six months. Oxygenation at the lower dosage for two months had beneficial effects on the colour and sensory quality of Pinotage wine. The higher oxygen dosage (all times) and longer times (all dosages) had a substantial detrimental effect on the overall sensory quality of the wine. A decrease in the TAC of the wine was observed for all the treatment combinations, despite increased concentrations of gallic acid. During the following harvest, a modified oxygenation treatment, entailing 1.0 mg O2/L in discrete doses every two weeks for two months, was tested. It had little effect on the wine phenolic composition and was not detrimental to the TAC of the wine. The modified oxygenation protocol significantly reduced the berry/ plum intensity of the Pinotage wine without negatively affecting the overall sensory quality. Oxygen addition on a continuous basis may also be less detrimental to the TAC of the wine and provide improved sensory quality.

Oenococcus oeni is the best malolactic bacterium adapted to low pH and the high SO2 and ethanol concentrations in wine. Leuconostoc mesenteroides and Leuconostoc paramesenteroides (now classified as Weissella paramesenteroides) have also been isolated from wine. Pediococcus damnosus is not often found in wine and is considered a contaminant of high pH wines. Pediococcus inopinatus, Pediococcus parvulus and Pediococcus pentosaceus have occasionally been isolated from wines. Lactobacillus brevis, Lactobacillus plantarum, Lactobacillus buchneri, Lactobacillus hilgardii (previously Lactobacillus vermiforme), Lactobacillus fructivorans (previously Lactobacillus trichoides and Lactobacillus heterohiochii) and Lactobacillus fermentum have been isolated from most wines. Lactobacillus hilgardii and L. fructivorans are resistant to high acid and alcohol and have been isolated from spoiled fortified wines. Lactobacillus vini, Lactobacillus lindneri, Lactobacillus nagelii and Lactobacillus kunkeei have been described more recently. The latter two species are known to cause sluggish or stuck alcoholic fermentations in wine. Although Lactobacillus collinoides and Lactobacillus mali (previously Lactobacillus yamanashiensis) decarboxylate L-malic acid, they are more often found in cider and fruit juices. Lactobacillus curvatus, Lactobacillus delbrueckii, Lactobacillus diolivorans, Lactobacillus jensenii and Lactobacillus paracasei are seldomly isolated from wines. Some strains of Lactobacillus casei may be closer related to Lactobacillus paracasei or a distant relative, Lactobacillus zeae. Oenococcus kitaharae, isolated from compost is genetically closely related to Oenococcus oeni, but does not decarboxylate malate, prefers higher growth pH and is phenotypically well distinguished from O. oeni. This review summarises the current taxonomic status of malolactic bacteria and lists key phenotypic characteristics that may be used to identify the species.

Industrial wine making confronts viticulturalists, wine makers, process engineers and scientists alike with a bewildering array of independent and semi-independent parameters that can in many cases only be optimized by trial and error. Furthermore, as most parameters are outside of individual control, predictability and consistency of the end product remain difficult to achieve. The traditional wine sciences of viticulture and oenology have been accumulating data sets and generating knowledge and know-how that has resulted in a significant optimization of the vine growing and wine making processes. However, much of these processes remain based on empirical and even anecdotal evidence, and only a small part of all the interactions and cause-effect relationships between individual input and output parameters is scientifically well understood. Indeed, the complexity of the process has prevented a deeper understanding of such interactions and causal relationships. New technologies and methods in the biological and chemical sciences, combined with improved tools of multivariate data analysis, open new opportunities to assess the entire vine growing and wine making process from a more holistic perspective. This review outlines the current efforts to use the tools of systems biology in particular to better understand complex industrial processes such as wine making.

Green tea extracts from the indigenous South African rooibos (Aspalathus linearis) and honeybush (Cyclopia species) plants were evaluated as potential antifungal agents against the plant pathogen Botrytis cinerea. When applied at 10 mg/ml, the tea extracts stimulated biomass production in B. cinerea by more than 3-fold after 24 hrs. This induction could not be linked directly to the presence of selected micro- and macronutrients or antioxidants in the extracts, suggesting a complex set of yet unidentified factors that may act synergistically to enhance cell growth. However, when applied at 100 mg/ml, the A. linearis and C. genistoides extracts reduced spore germination of B. cinerea by 33.3% and 16.7%, respectively. This suggests that the tea extracts contain active compounds that should be further investigated for their potential as natural anti-fungal agents.

Wine comprises a complex microbial ecology of opportunistic microorganisms, some of which could potentially induce spoilage and result in consequent economic losses under uncontrolled conditions. Yeasts of the genus Brettanomyces, or its teleomorph Dekkera, have been indicated to affect the chemical composition of the must and wine by producing various metabolites that are detrimental to the organoleptic properties of the final product. These yeasts can persist throughout the harsh winemaking process and have in recent years become a major oenological concern worldwide. This literature review summarises the main research focus areas on yeasts of the genera Brettanomyces and Dekkera in wine. Specific attention is given to the spoilage compounds produced, the methods of detection and isolation from the winemaking environment and the factors for controlling and managing Brettanomyces spoilage.

Fourteen cultivars and clones, mainly selected from the island of Sardinia (Italy) and grown in a collection field, showed significant quantitative differences in phenolic potential. An extraction method designed to reproduce the winemaking process was used to determine the amounts of extractable polyphenols, anthocyanins, catechins and proanthocyanidins reactive to vanillin, and the proanthocyanidins in grape skins and seeds. The Sardinian cultivar Nieddera and the Spanish cultivar Graciano had the highest concentrations of extractable polyphenols, anthocyanins, catechins and proanthocyanidins reactive to vanillin. Four clones of the Cannonau cultivar (synonym Grenache) exhibited fairly high variability, with significant differences in berry and seed phenolic contents.

The effect of oak contact on the phenolic composition, total antioxidant capacity (TAC) and colour of Pinotage wines was investigated during maturation. Oak maturation included traditional treatments, such as new, second-fill and third-fill barrels, as well as alternative treatments (oak chips, staves, extract and dust) applied in old barrels over a period of 28 weeks. Oak maturation using traditional and alternative treatments improved the objective colour of Pinotage wine by decreasing the L* value. Losses in TAC caused by decreased concentrations of monomeric phenolic compounds (most anthocyanins, flavan-3-ols, flavonols and hydroxycinnamic acids) during oak maturation were negated by increased concentrations of gallic acid and the formation of new oligomeric and polymeric pigments. Wine maturation in stainless steel containers also resulted in a decrease in anthocyanin content. The decrease in phenolic acid content for wines matured in stainless steel was less pronounced, while their flavan-3-ol content remained stable. The new-barrel treatment had the most pronounced effect on all parameters. Oak maturation can be used for the production of Pinotage wine when the retention of TAC is a high priority.

In this study the culture-independent technique, polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE), was investigated for the early detection and identification of possible spoilage microbes in wine. PCR and DGGE conditions were successfully optimised with the universal primers HDA1GC and HDA2, the bacteria-specific primers WBAC1GC-WBAC2, and the yeast-specific primers NL1GC and LS2. PCR and DGGE detection limits were determined for Lactobacillus plantarum, Pediococcus pentosaceus, Acetobacter pasteurianus and Brettanomyces bruxellensis when inoculated into sterile saline solution (SSS) and white wine at 106 cfu/mL respectively. PCR detection limits were more sensitive (101 to 102 cfu/mL) than DGGE detection limits (101 to 104 cfu/ mL), with the exception of B. bruxellensis, which had higher PCR and DGGE detection limits than the other reference microbes. PCR-DGGE analysis was also used successfully to detect and identify Lb. plantarum, A. pasteurianus and B. bruxellensis at a concentration of 108 cfu/mL as part of mixed populations in SSS and white wine. PCR detection limits of 101 cfu/mL were determined for all three reference microbes in mixed populations. The DGGE detection limits were higher for mixed populations when compared to single strains.

This paper presents a study of precision agriculture in the wine industry. While precision viticulture mostly aims to maximise yields by delivering the right inputs to appropriate places on a farm in the correct doses and at the right time, the objective of this study was rather to assess vine biomass differences. The solution proposed in this paper uses aerial imagery as the primary source of data for vine analysis. The first objective to be achieved by the solution is to automatically identify vineyards blocks, vine rows, and individual vines within rows. This is made possible through a series of enhancements and hierarchical segmentations of the aerial images. The second objective is to determine the correlation of image data with the biophysical data (yield and pruning mass) of each vine. A multispectral aerial image is used to compute vegetation indices, which serve as indicators of biophysical measures. The results of the automatic detection are compared against a test field, to verify both vine location and vegetation index correlation with relevant vine parameters. The advantage of this technique is that it functions in environments where active cover crop growth between vines is evident and where variable vine canopy conditions are present within a vineyard block.

A literature study was carried out to determine what is currently known about the contamination of irrigation water with plant-parasitic nematodes, and what control measures are currently available. Contamination sources of irrigation water with plant-parasitic nematodes were investigated, including wells, boreholes, collected rainwater, ponds, lakes, dams, rivers, municipal water, runoff water, irrigation canals and drainage water in soilless culture. Only when the origin of irrigation water was a capped borehole was the risk of contamination with plant-parasitic nematodes low. The plant-parasitic nematodes of economic importance to grapevine reported to be found in irrigation water were Meloidogyne spp., Xiphinema spp., Tylenchulus semipenetrans, Trichodorus sp., Criconemoides xenoplax and Pratylenchus spp. The different sampling techniques used for the detection and monitoring of plant-parasitic nematodes and the sampling time and location are listed. The survival and infection potential reported for each species of plant-parasitic nematode found in irrigation water was noted. Serious nematode parasites of grapevines, such as Meloidogyne javanica, can survive for 16 to 32 days, M. incognita, for up to 14 days, Pratylenchus, for up to 70 days, T. semipenetrans, for up to 128 days, and X. index, for up to 13 days in irrigation water. All reported techniques used for the management of nematodes in irrigation water are listed and possible future research into the control of plant-parasitic nematodes in irrigation water is discussed. From this review, substantial evidence was obtained of the danger of introducing plant-parasitic nematodes to grapevine production sites by means of irrigation water.

Lutein and beta-carotene were heated in H2S04 and ethanol/tartaric acid media adjusted to pH 1 and 3, respectively. Various products were formed, but 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN), responsible for the kerosene-like flavour of aged Weisser Riesling wines, derived from lutein only.

In a trial under semi-controlled conditions, Merlot grapevines on 101-14Mgt and 110 Richter (110R) rootstocks were grown in virgin soils developed in highly weathered parent materials derived mainly from granite and metasediment (shale). Each soil was irrigated at c. -0.075 MPa. The clay fractions of both soils were dominated by kaollnite. Lime and P were supplied, but no K. Bray II soil K levels from both parent materials were similar in the field state, but lower in the shale than in the granite when averaged over the trial period. Petiole K concentrations did not differ between rootstocks on the granite, but on the shale soils were higher in the vines on 101-14Mgt than on 110R. The granite x 101-14Mgt treatment significantly promoted (p ≤5 0.05) greater trunk circumferences, cane mass, leaf areas and overall wine quality than the shale x 11OR treatment. Yields from grapevines in the granite x 11OR and granite x 101-14Mgt treatments did not differ significantly. However, the granite x 101-14Mgt treatment produced higher yields than the shale x 101-14Mgt and shale x 11OR treatments. These differences were attributed to an interaction between the soil and rootstock, with K availabifity and uptake as contributory factors.

The correlation between the 11B/10B ratio in grapevine leaves and that in the growth medium was established in a series of hydroponic experiments with grapevine cuttings for different cultivar/rootstocks combinations. The hydroponic growth medium was alternately spiked with boric acid containing B with natural isotope composition and B enriched in 10B, so as to vary the 11B/10B ratio. B isotope ratios in grapevine leaves were determined by quadrupole-based ICP-MS after digestion and complete matrix removal through microwave digestion and isolation of matrix-free B species using ion exchange separation. It was found that the B isotope ratios in the leaves were not identical to those in the growth medium, but that a change in the ratio in the growth medium induced a similar change in the leaves. For a particular cultivar/rootstock combination, a characteristic B isotope ratio was found that was different from the ratio in a group of plants with a different cultivar/rootstock combination.