Research Articles (Viticulture and Oenology)

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The 3Ps (Profit, Planet, and People) of sustainability amidst climate change : a South African grape and wine perspective
(MDPI, 2021-03-08) Gbejewoh, Omamuyovwi; Keesstra, Saskia; Blancquaert, Erna
Conventional agriculture has made the search for sustainability urgent, more so with regards to climate change. This has extended to the grape and wine industry, an important industry in South Africa in terms of labor employment and foreign exchange. This paper aims to review the current state of knowledge with regards to the three pillars of sustainability and with regards to climate change. In order to understand sustainability in South Africa, a historical context is needed, because the welfare of farm workers still retains vestiges of past Apartheid. Ecological responsibility and higher profits are the main reasons for sustainable practices. Additionally, water use, chemical use, and soil erosion are important environmental sustainability concerns. With regards to climate change, in terms of economic sustainability, there will be winners and losers and social sustainability issues will intensify as changes occur in farms. Table grape producers are relatively more profitable than wine grape producers. Furthermore, pest, disease, irrigation pressure will worsen as the climate warms. However, there are long- and short-term adaptation strategies such as changes in viticulture practices and grape cultivars, respectively, to stem the effects of climate change, but this may be stymied by cost and farmers’ perceptions of climate change.
Additions of glutathione or specific glutathione-rich dry inactivated yeast preparation (DYP) to sauvignon blanc must : effect on wine chemical and sensory composition
(South African Society for Enology and Viticulture, 2017) Gabrielli, M.; Aleixandre-Tudo, J. L.; Kilmartin, P. A.; Sieczkowski, N.; Du Toit, W. J.
Although the addition of pure glutathione (GSH) is not allowed under current regulations, the concentration of this compound can be increased in wine through the addition of glutathione-enriched dry yeast preparations (DYP). These preparations have been observed to have antioxidant properties and could thus influence wine aroma and sensory characteristics. The main aim of this study was to investigate the effect of DYP and GSH juice additions on the sensory and chemical composition of Sauvignon blanc wine. Four juice additions were performed and compared against a control treatment: 5.5 mg/L of GSH; 0.4 g/L of DYP; 80 mg/L of GSH; 0.4 g/L of DYP plus 80 mg/L of GSH. After three months of bottling, the volatile and sensorial composition was investigated. The addition of DYP preparations to must increased the concentration of certain wine volatile compounds, with increased attributes of riper tropical fruit aromas, which was not always observed with the GSH additions. The addition of DYP influenced the concentrations of some volatile compounds, which modified the white wine aroma. The release of compounds other than GSH by the yeast products is proposed as the reason for these changes. The results observed in this study can assist winemakers to modify the aroma profile of Sauvignon blanc wines.
Altered fermentation performances, growth, and metabolic footprints reveal competition for nutrients between yeast species inoculated in synthetic grape juice-like medium
(Frontiers Media, 2018) Rollero, Stephanie; Bloem, Audrey; Ortiz-Julien, Anne; Camarasa, Carole; Divol, Benoit
The sequential inoculation of non-Saccharomyces yeasts and Saccharomyces cerevisiae in grape juice is becoming an increasingly popular practice to diversify wine styles and/or to obtain more complex wines with a peculiar microbial footprint. One of the main interactions is competition for nutrients, especially nitrogen sources, that directly impacts not only fermentation performance but also the production of aroma compounds. In order to better understand the interactions taking place between non-Saccharomyces yeasts and S. cerevisiae during alcoholic fermentation, sequential inoculations of three yeast species (Pichia burtonii, Kluyveromyces marxianus, Zygoascus meyerae) with S. cerevisiae were performed individually in a synthetic medium. Different species-dependent interactions were evidenced. Indeed, the three sequential inoculations resulted in three different behaviors in terms of growth. P. burtonii and Z. meyerae declined after the inoculation of S. cerevisiae which promptly outcompeted the other two species. However, while the presence of P. burtonii did not impact the fermentation kinetics of S. cerevisiae, that of Z. meyerae rendered the overall kinetics very slow and with no clear exponential phase. K. marxianus and S. cerevisiae both declined and became undetectable before fermentation completion. The results also demonstrated that yeasts differed in their preference for nitrogen sources. Unlike Z. meyerae and P. burtonii, K. marxianus appeared to be a competitor for S. cerevisiae (as evidenced by the uptake of ammonium and amino acids), thereby explaining the resulting stuck fermentation. Nevertheless, the results suggested that competition for other nutrients (probably vitamins) occurred during the sequential inoculation of Z. meyerae with S. cerevisiae. The metabolic footprint of the non-Saccharomyces yeasts determined after 48 h of fermentation remained until the end of fermentation and combined with that of S. cerevisiae. For instance, fermentations performed with K. marxianus were characterized by the formation of phenylethanol and phenylethyl acetate, while those performed with P. burtonii or Z. meyerae displayed higher production of isoamyl alcohol and ethyl esters. When considering sequential inoculation of yeasts, the nutritional requirements of the yeasts used should be carefully considered and adjusted accordingly. Finally, our chemical data suggests that the organoleptic properties of the wine are altered in a species specific manner.
Anatomical responses to cytokinins of abscised grapevine shoot apices cultured in vitro
(South African Society for Enology and Viticulture, 1987) Goussard, P. G.
Responses of excised shoot apices of V. vinifera L. cv. Chenin blanc to different cytokinin treatments were studied at various intervals (days) after the start of in vitro culture, using light and scanning electron microscopy. Results clearly indicated that in vitro produced shoots were of axillary origin. Shoot clusters were produced by the enhanced release of axillary meristems from apical dominance, due to the application of 6-benzylaminopurine (BAP) singly as well as in combination with zeatin riboside (ZR). Axillary meristems on these axillary shoots were subsequently released from apical dominance, thus giving rise to shoot clusters of high densities. Shoot clusters induced by ZR alone were less dense, probably due to an initial delay in elongation of axillary meristems nearest to the main apical meristem of the shoot. However, elongation of axillary meristems lower down the axes proceeded strongly in the presence of ZR. Application of BAP resulted in more pronounced release of axillary meristems from apical dominance than with ZR.
Basic in-mouth attribute evaluation : a comparison of two panels
(MDPI, 2018-12-21) Mihnea, Mihaela; Aleixandre-Tudo, Jose Luis; Kidd, Martin; Du Toit, Wessel
Astringency is often difficult to evaluate accurately in wine because of its complexity. This accuracy can improve through training sessions, but it can be time-consuming and expensive. A way to reduce these costs can be the use of wine experts, who are known to be reliable evaluators. Therefore, the aim of this work was to compare the sensory results and the panel performance obtained using trained panelists versus wine experts (winemakers). Judges evaluated twelve red wines for in-mouth basic perception (sweet, sour, bitter, astringent, and burning sensation) following the same tasting protocol and with the samples being presented in two different tasting modalities. Panels’ performance and relationship between the chemical composition and the sensory perception were investigated. Both panels showed similar consistency and repeatability, and they were able to accurately measure the astringency of the wines. However, the significant correlations between sensory scores and chemical composition varied with the panel and the tasting modality. From our results, we could see that winemakers tended to discriminate better between the samples when the differences were very small.
Berry size variation of vitis vinifera l. Cv. Syrah : morphological dimensions, berry composition and wine quality
(South African Society for Enology and Viticulture, 2015) Melo, M. S.; Schultz, H. R.; Volschenk, C. G.; Hunter, J. J.
Berry size has always been a quality factor in wine production. In this study, Syrah grapes from a single vineyard were classified into different size groups according to diameter: small (< 13 mm), medium (13 < diameter < 14 mm) and large (> 14 mm). Smaller berries were present in the highest and larger berries in the lowest numbers. Size distributions were similar in both seasons (2010/2011 and 2011/2012). Berry physical characteristics (mass, volume and skin area) increased with size, showing the same tendency in both years. Positive correlations between berry mass, volume and skin area were found, whereas these variables were negatively related with berry number/kg grapes. Berry volume was negatively correlated with dry skin weight. Skin surface area/berry volume seems to be an indicator of the “dilution” effect associated with increasing size, as larger berries presented the lowest values. In 2012 the grapes were harvested at a higher soluble solid level than in the previous year; large-sized berries presented the lowest levels in both years. The whole-berry analysis of total anthocyanins showed a decrease in concentration and increase in content per berry, from smaller to larger berries. Small berries and the control (naturally occurring berry size mixture) showed a higher extractability of anthocyanins and phenolic compounds than the medium and large berries. Sensorially, wines from medium berries were more consistent over the two years, scoring higher than the rest. Berry sizes were related to wine style differences, and knowing the population of berry sizes in the vineyard close to harvest would offer a possibility to predict wine styles.
Bibliometric analysis of publications by South African viticulture and oenology research centres
(Academy of Science of South Africa, 2012-05-28) Aleixandre-Benavent, Rafael; Aleixandre-Tudo, Jose L.; Alcaide, Gregorio Gonzalez; Ferrer-Sapena, Antonia; Aleixandre, Jose L.; Du Toit, Wessel
We analysed the production, impact factor of, and scientific collaboration involved in viticulture and oenology articles associated with South African research centres published in international journals during the period 1990-2009. The articles under scrutiny were obtained from the Science Citation Index database, accessed via the Web of Knowledge platform. The search strategy employed specific viticulture and oenology terms and was restricted to the field 'topic'. The results showed that 406 articles were published during the review period, with the most number of publications being in the South African Journal of Enology and Viticulture (n = 34), American Journal of Enology and Viticulture (n = 16) and Journal of Agricultural and Food Chemistry (n = 16). The articles were published by 851 authors from 236 institutions. The collaboration rate was 3.7 authors per article, having grown over the two decades examined. The most productive institutions (i.e. those receiving a greater number of citations) were Stellenbosch University (219 published articles and 2592 citations) and the Agricultural Research Council (49 published articles and 454 citations), both from South Africa. Graphical representation of co-authorship networks identified 18 groups of authors and a single network of institutions whose core is Stellenbosch University. In conclusion, we have identified a significant growth in South African viticulture and oenology research in recent years, with a high degree of internationalisation and a constant level of domestic collaboration. © 2012. The Authors.
Bibliometric and social network analysis in scientific research on precision agriculture
(Indian Academy of Sciences, 2018-11-10) Aleixandre-Tudo, Jose Luis; Castello-Cogollos, Lourdes; Aleixandre, Jose Luis; Aleixandre-Benavent, Rafael
Precision agriculture (PA) is used to improve agricultural processes. A better understanding of PA as well as the evolution of the research status through the available literature are reported and discussed in this study. The Web of Science (WoS) was used to obtain the research records under study. Indicators of scientific productivity, collaboration between countries and research impact were evaluated through a social network analysis. The keywords included in the publications and subject areas under which the research was published were also evaluated through subject analysis. A total of 2027 articles were analysed from 1994 to 2014. The most productive journals were ‘Computers and Electronics in Agriculture’ (n = 191) and ‘Precision Agriculture’ (n = 110). The most frequent keywords were ‘management’ (n = 243), ‘yield’ (n = 231), ‘soil’ (n = 198) and ‘variability’ (n = 190). The collaboration network showed the United States occupying a central position, in combination with some leading countries such as Brazil, Germany, People’s Republic of China, Canada, Australia and Spain. A steady increase in PA research was identified during the last decade, which was even more sharp between 2010 and 2014. The increased importance of PA research has recently led to the birth of specific journals such as Precision Agriculture. The increasing number of journals that publish articles related to the topics included in the WoS must also be considered. The network analysis identified a number of developed countries in the hotspot of international collaboration.
Biogenic amines in wine : understanding the headache
(SASEV, 2008-09) Smit, A. Y.; Du Toit, W. J.; Du Toit, M.
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.
Biological deacidification of musts induced by yeasts or malolactic bacteria and the effect on wine quality
(South African Society for Enology and Viticulture, 1987) Van Rooyen, T. J.; Tracey, R. P.
This study investigated the possible use of Schizosaccharomyces pombe and Schizosaccharomyces malidevorans for deacidification of red wines during alcoholic fermentation, in comparison with existing deacidification practices of induced or spontaneous malolactic fermentation (MLF) in South Africa. In red must, the effect of these yeasts on alcoholic fermentation rate, rate of L-malic acid removal, as well as the effect of mixed cultures with Saccharomyces cerevisiae at different inoculum concentrations and sizes of inocula on wine quality was investigated. In white must, the effect of pure culture inocula and temperature on wine quality and production of volatile bouquet substances was also studied. Both Schizosaccharomyces spp. were found to deacidify normal concentrations of L-malic acid in musts effectively at higher growth temperatures, but the ability of Schiz. pombe was inhibited by high concentrations of Lmalic acid which was not pH dependent. Certain key volatile fermentation bouquet compounds were produced in very low quantities, which seems to be the reason for poor sensory quality wines produced by Schizosaccharomyces.
Calibration of the surface renewal method (SR) under different meteorological conditions in an avocado orchard
(MDPI, 2020-05-19) Moran, Andres; Ferreyra, Raul; Selles, Gabriel; Salgado, Eduardo; Caceres-Mella, Alejandro; Poblete-Echeverria, Carlos
The surface renewal method (SR) allows estimating the sensible heat flux (H) using high-frequency thermocouples. Traditionally, SR has been compared and calibrated using standard instruments such as the Eddy covariance system (EC). Calibration involves correcting H measured with SR (H’SR) by means of the calibration factor (α). However, several studies show that α is not constant and could depend on canopy architecture, measurement height, atmospheric stability, and weather conditions. In avocado orchards, there is not enough information about energy fluxes and the application of the SR method. Therefore, the objective of this study is to calibrate the SR method in a mature avocado orchard considering the effect of meteorological conditions on the determination of α. The components of the surface energy balance were measured using an EC system in a commercial avocado orchard (cv. Hass) located in the Aconcagua Valley, Valparaíso Region, Chile. To evaluate the effect of the meteorological conditions on the determination of α, the dataset was classified into nine categories based on solar radiation and wind intensity. The results show that α varies according to meteorological conditions, with significant differences for cloudy days. The use of the variable α reduced the error in estimating H, so, this methodology can be used to have a more precise approximation of the energy balance and therefore to the water requirements.
Carotenoid levels in maturing grapes as affected by climatic regions, sunlight and shade
(South African Society for Enology and Viticulture, 1991) Marais, J.; Van Wyk, C. J.; Rapp, A.
The effect of climatic region, degree of ripeness, sunlight and shade on carotenoid concentrations in Weisser Riesling and Chenin blanc grapes was investigated. Lutein and beta-carotene concentrations were higher in grapes from hot regions than grapes from cooler regions. In general, decreases in carotenoid concentrations were observed with an increase in ripeness. Also, grapes exposed to sunlight generally had lower carotenoid concentrations than shaded grapes. Both lutein and beta-carotene concentrations varied little between Weisser Riesling and Chenin blanc grapes at comparable ripening stages.
Changes in carbohydrates in nursery-grown grapevine rootstocks
(South African Society for Enology and Viticulture, 1983) Uys, D. C.; Orffer, C. J.
The utilisation and accumulation of sugar, starch and hemicellulose were studied in nursery-grown grapevine rootstocks. For an initial period lasting about 12 weeks all three components were utilised to varying degrees by the cuttings. Subsequently, starch and hemicellulose increased in the stem (original cutting) of the plant, while sugar remained low until the onset of winter. In the shoots, hemicellulose accumulation was very marked, whereas in the roots starch was the dominant carbohydrate component.
Characterisation of pinotage wine during maturation on different oak products
(SASEV, 2008-01) De Beer, D.; Joubert, E.; Marais, J.; Du Toit, W.; Fourie, B.; Manley, M.
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.
Characterisation of the aroma of the hybrid Ferdinand de Lesseps (Vitis vinifera x Vitis labrusca)
(South African Society for Enology and Viticulture, 2000) Rogers, I. M.; Van Wyk, C. J.
Freon 11-extracted volatiles of Ferdinand de Lesseps grape juice were studied by capillary gas chromatography, capillary gas chromatography-mass spectrometry and gas chromatography-sniffing. The berries were crushed under an inert atmosphere and the juice extracted with Freon 11 for 20 hours. Thirty-one compounds were reported. The juice was quantitatively characterised mostly by esters, particularly hydroxy esters. These esters are most probably responsible for the sweetish pineapple aroma of Ferdinand de Lesseps grapes whereas o-aminoacetophenone and 2,5-dimethyl-4-hydroxy-3(2H)-furanone could contribute to its hybrid note.
A chemometric approach to the evaluation of the ageing ability of red wines
(Elsevier, 2020) Aleixandre-Tudo, Jose Luis; Toit, Wesseldu
One of the most important quality attributes of red wines is its ability to withstand and ageing process. The multidimensionality of the ageing ability concept, which includes a combination of colour, taste, mouthfeel, and aroma was reported in previous studies. Phenolic compounds are largely or partially involved in most of these wine attributes and have been proposed as potential candidates to evaluate the ageing ability of red wines. The phenolic and colour properties of a large number of wines were measured during a barrel and bottle ageing process of 24 months. To our understanding, a wine that needs the longest time to reach optimal phenolic quality is considered a wine with higher ability to age (concentration assumption). Moreover, a wine that is able to maintain its optimal phenolic quality for longer will also be a wine with high ageing ability (stability assumption). Based on the formulated assumptions a scoring system was used to identify those wines with theoretically high ability to age. As expected, these wines contained initial high levels of tannins, total phenols and anthocyanins, including high polymeric pigment presence and enhanced colour properties. Interestingly, high ageing ability wines showed a smaller change in the colour properties over time which might be indicating slower pigment formation rates. In addition, a chemometric attempt was undertaken to explore an ageing index based on initial phenolic content. The evolution of the index over time using a multi-block approach showed stability for the index values, in line with the short term stability of tannin and total phenol levels. Finally, promising results were obtained as two thirds of the wines were correctly classified when a validation task between the ageing index and the score values was attempted.
Chenin blanc wine volatiles and the intensity of a guava-like flavour
(South African Society for Enology and Viticulture, 1982) Van Rooyen, P. C.; De Wet, P.; Van Wyk, C. J.; Tromp, A.
A guava-like flavour occurring in some South African Chenin blanc and Colombard dry white wines was investigated. Headspace volatiles of some of these wines, as well as those of fresh guava fruits, were analysed by means of a gas chromatograph equipped with a "sniffer-detector". In contrast to the headspace concentrate of guava fruits, no single fraction with a typical guava flavour was found in the wines analysed. The pattern recognition system "ARTHUR" was therefore used to investigate relationships between the more important wine volatiles and the intensity of a guava-like flavour of a set of wines originating from the same Chenin blanc must. Sensory scores for this flavour were used in both category and continuous property analysis in each case. Category and correlation to property plots were used to elucidate the results. Several promising variables and ratios between variables were singled out for further investigation, notably ethyl butyrate and the ratios ethyl butyrate/ethyl decanoate and ethyl butyrate/ethyl octanoate.
Co-flocculation of yeast species, a new mechanism to govern population dynamics in microbial ecosystems
(Public Library of Science, 2015) Rossouw, D.; Bagheri, Bahareh; Setati, Mathabatha Evodia; Bauer, Florian
Flocculation has primarily been studied as an important technological property of Saccharomyces cerevisiae yeast strains in fermentation processes such as brewing and winemaking. These studies have led to the identification of a group of closely related genes, referred to as the FLO gene family, which controls the flocculation phenotype. All naturally occurring S. cerevisiae strains assessed thus far possess at least four independent copies of structurally similar FLO genes, namely FLO1, FLO5, FLO9 and FLO10. The genes appear to differ primarily by the degree of flocculation induced by their expression. However, the reason for the existence of a large family of very similar genes, all involved in the same phenotype, has remained unclear. In natural ecosystems, and in wine production, S. cerevisiae growth together and competes with a large number of other Saccharomyces and many more non-Saccharomyces yeast species. Our data show that many strains of such wine-related non-Saccharomyces species, some of which have recently attracted significant biotechnological interest as they contribute positively to fermentation and wine character, were able to flocculate efficiently. The data also show that both flocculent and non-flocculent S. cerevisiae strains formed mixed species flocs (a process hereafter referred to as co-flocculation) with some of these non-Saccharomyces yeasts. This ability of yeast strains to impact flocculation behaviour of other species in mixed inocula has not been described previously. Further investigation into the genetic regulation of co-flocculation revealed that different FLO genes impact differently on such adhesion phenotypes, favouring adhesion with some species while excluding other species from such mixed flocs. The data therefore strongly suggest that FLO genes govern the selective association of S. cerevisiae with specific species of non-Saccharomyces yeasts, and may therefore be drivers of ecosystem organisational patterns. Our data provide, for the first time, insights into the role of the FLO gene family beyond intraspecies cellular association, and suggest a wider evolutionary role for the FLO genes. Such a role would explain the evolutionary persistence of a large multigene family of genes with apparently similar function.
Comparative (within species) genomics of the vitis vinifera L. terpene synthase family to explore the impact of genotypic variation using phased diploid genomes
(Frontiers Media, 2020) Smit, Samuel Jacobus; Vivier, Melane Alethea; Young, Philip Richard
The Vitis vinifera L. terpene synthase (VviTPS) family was comprehensively annotated on the phased diploid genomes of three closely related cultivars: Cabernet Sauvignon, Carménère and Chardonnay. VviTPS gene regions were grouped to chromosomes, with the haplotig assemblies used to identify allelic variants. Functional predictions of the VviTPS subfamilies were performed using enzyme active site phylogenies resulting in the putative identification of the initial substrate and cyclization mechanism of VviTPS enzymes. Subsequent groupings into conserved catalytic mechanisms was coupled with an analysis of cultivar-specific gene duplications, resulting in the identification of conserved and unique VviTPS clusters. These findings are presented as a collection of interactive networks where any VviTPS of interest can be queried through BLAST, allowing for a rapid identification of VviTPS-subfamily, enzyme mechanism and degree of connectivity (i.e., extent of duplication). The comparative genomic analyses presented expands our understanding of the VviTPS family and provides numerous new gene models from three diploid genomes.
A comparative anatomical study of the grapevine shoot : I Epidermis
(South African Society for Enology and Viticulture, 1984) Swanepoel, J. J.; De la Harpe, A. C.; Orffer, C. J.
Material gathered from three positions on the shoot and cane during veraison and two weeks after harvest were investigated for taxonomic features concerning the epidermis. Stomata and lenticels were present in all the cultivars studied, but trichomes were frequently present only on 99 Richter. Based on epidermal characteristics a dendogram giving the percentage similarity between cultivars, was constructed, and from this was concluded that concerning taxonomic features on Vitis vinifera L. cultivars tend to have a more than 90% similarity irrespective of the position on the shoot.

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