South African Grape Research Articles

The 3Ps (Profit, Planet, and People) of Sustainability amidst Climate Change: A South African Grape and Wine Perspective

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.

Is There a Link Between Coffee Aroma and the Level of Furanmethanethiol (FMT) in Pinotage Wines

Over the years, Pinotage has found its way into the South African and international market. Producers have used the flavour potential of this “original” South African grape to produce different wine styles, one of them being the so-called “coffee-style Pinotage”. The current study aims to explain the impact of furanmethanethiol (FMT) on the characteristic coffee aroma of these coffee-style wines. Chemical and sensory evaluation, as well as data mining of the technical information available, was performed. Not all wines marketed as “coffee Pinotage” showed a high “coffee” rating. However, the results showed a good correlation between the aroma perception and FMT concentrations (R2 = 0.81). However, RV coefficients were low when comparing the coffee rating with the information provided on both the front and the back label, which shows that, in some cases, the use of the “coffee Pinotage” term was rather part of the marketing strategy.

Microbial diversity in grape musts from Austrian and South African grape varieties and regions

Vitis vinifera is one of the most widely planted crops and holds important economic value in South Africa and Austria. Grapes obtained from this plant harbour a complex fungal community which plays a crucial role in the wine fermentation process and influences wine flavour and aroma. For many years the contributions of the natural yeasts has been eclipsed by the use of active dry yeast (ADY) inoculant, mainly of the species Saccharomyces cerevisiae. However, recent studies show a growing interest in deciphering the natural microbial diversity and in promoting its persistence during fermentation in order to enhance wine typicity. The current preliminary study aims to provide a first broad assessment of the fungal community fingerprint of different grape varietals from different wine producing areas in Austria and South Africa through Automated Ribosomal Intergenic Spacer Analysis (ARISA). The ARISA profiles separated the samples according to country of origin, and suggested some regional and varietal separation within each country. Future work will evaluate the contribution of these fungal communities to wine chemical composition and sensorial distinctness.

The Impact of Saccharomyces cerevisiae on a Wine Yeast Consortium in Natural and Inoculated Fermentations.

Natural, also referred to as spontaneous wine fermentations, are carried out by the native microbiota of the grape juice, without inoculation of selected, industrially produced yeast or bacterial strains. Such fermentations are commonly initiated by non-Saccharomyces yeast species that numerically dominate the must. Community composition and numerical dominance of species vary significantly between individual musts, but Saccharomyces cerevisiae will in most cases dominate the late stages of the fermentation and complete the process. Nevertheless, non-Saccharomyces species contribute significantly, positively or negatively, to the character and quality of the final product. The contribution is species and strain dependent and will depend on each species or strain’s absolute and relative contribution to total metabolically active biomass, and will therefore, be a function of its relative fitness within the microbial ecosystem. However, the population dynamics of multispecies fermentations are not well understood. Consequently, the oenological potential of the microbiome in any given grape must, can currently not be evaluated or predicted. To better characterize the rules that govern the complex wine microbial ecosystem, a model yeast consortium comprising eight species commonly encountered in South African grape musts and an ARISA based method to monitor their dynamics were developed and validated. The dynamics of these species were evaluated in synthetic must in the presence or absence of S. cerevisiae using direct viable counts and ARISA. The data show that S. cerevisiae specifically suppresses certain species while appearing to favor the persistence of other species. Growth dynamics in Chenin blanc grape must fermentation was monitored only through viable counts. The interactions observed in the synthetic must, were upheld in the natural must fermentations, suggesting the broad applicability of the observed ecosystem dynamics. Importantly, the presence of indigenous yeast populations did not appear to affect the broad interaction patterns between the consortium species. The data show that the wine ecosystem is characterized by both mutually supportive and inhibitory species. The current study presents a first step in the development of a model to predict the oenological potential of any given wine mycobiome.

Exploring the phenotypic space of non-Saccharomyces wine yeast biodiversity

Tremendous microbial diversity exists in vineyards, and the potential to harness this diversity for novel mixed or pure starter cultures for wine fermentation has received significant attention in recent years. However, most studies are limited to a small subset of strains and species. Here we present data from a systematic screen of 91 yeast isolates from South African grape must and vineyard samples for oenologically relevant traits. One focus area was finding non-Saccharomyces isolates showing both reduced ethanol yields, as well as improved aromatic characteristics. Of the 91 isolates evaluated initially, 21 showed lower ethanol yields when compared to commercial wine yeast strain controls. Collectively, the metabolic data (primary fermentation and secondary aroma compounds) highlight the enormity of the ‘phenotypic space’ of yeast communities in South African vineyards. The data also emphasise intraspecies variability, challenging our concept of species typicity. Of particular oenological interest was the ability of several isolates to produce high levels of terpenoid compounds. A few strains were ultimately found which showed a substantial reduction (>1.5%) in the final ethanol content of sequential fermentations, as well as unique aroma compound production profiles. Four of these strains were selected for comprehensive wine trials in both red and white grape musts, complete with microbial, chemical and sensory analyses of the red wines. This presents, for the first time, a full bench-to-bottle characterisation of non-Saccharomyces strains showing the most potential for commercial application.The findings of this study enlarge the potential range of oenological applications for non-Saccharomyces yeast, while also suggesting the potential usefulness of several yeast species that have previously not been considered for winemaking applications.

PCR detection of enzyme-encoding genes in Leuconostoc mesenteroides strains of wine origin

Fifteen isolates of lactic acid bacteria originating from South African grape and wine samples were identified as Leuconostoc mesenteroides subsp. mesenteroides through the taxonomic analysis of their 16S rDNA gene sequences. These isolates were further tested for the presence of genes coding for enzymes of oenological relevance using PCR detection technique. A type strain of Leuc. mesenteroides (NCDO 529(T)) was also incorporated for comparative analysis. From the PCR detection results, the estA, prtP, alsD, alsS, metK, metC and metB genes were present in all the strains tested. The bgl and gshR genes encoding β-glucosidase and glutathione reductase, respectively, were not detected in some strains. On the other hand, none of the tested strains possessed the genes encoding phenolic acid decarboxylase (padA), citrate permease (citP), citrate lyase (citD, citE and citF) and arginine deiminase pathway enzymes (arcA, arcB and arcC). The verification of PCR-generated fragments was performed by sequencing. GenBank database was used to search for homologous DNA sequences. Neighbour-joining trees based on nucleotide sequences of alsS, estA, metK and mleA genes were also constructed in order to study the phylogenetic relationship between Leuc. mesenteroides strains and closely related species. The phylogenetic analyses revealed that there are genetic heterogeneities between strains of Leuc. mesenteroides species. In conclusion, this study has improved our knowledge on the genetics of oenological strains of Leuc. mesenteroides and their genetic potential to contribute to certain wine aroma compounds.

Identification and characterization of Lactobacillus florum strains isolated from South African grape and wine samples

A total of 213 strains of lactic acid bacteria were examined in this study. Among these, 30 strains previously isolated from South African grape and wine samples remained unidentified. The identification of these isolates was performed by BLAST and phylogenetic analyses of 16S rDNA gene sequences, which indicated that the isolates belonged to Lactobacillus florum. In this work, we also designed a discriminative species-specific primer FLOR targeting the 16S rDNA gene of Lb. florum. The validity and specificity of this primer was confirmed. Of particular interest in this study was to further evaluate the identified strains for the presence of genes encoding enzymes of oenological relevance. Reference strains included three flower-associated Lb. florum (F9-1(T), F9-2 and F17) and two Lactobacillus lindneri (AWRI B530 and DSM 20691) strains. Lb. lindneri strains were incorporated as being the closest relatives of Lb. florum. PCR detection results revealed that all Lb. florum strains and Lb. lindneri AWRI B530 (grape isolate) possessed the majority of the tested genes relative to DSM 20691 (beer isolate); these enzyme-encoding genes included malolactic enzyme, peptidases (PepC, PepI, PepN), citrate lyase (α- and β-subunits), phenolic acid decarboxylase and arginine deiminase pathway enzymes (arginine deiminase and ornithine transcarbamylase). Sequence verification of PCR-generated fragments was performed by sequencing. The sequence data were used to construct the phylogenetic trees, which indicated that our Lb. florum isolates cluster with other Lb. florum strains of flower origin but rather distinct from other LAB species, with Lb. lindneri being the next closest species.

Genetic screening of wine-related enzymes inLactobacillusspecies isolated from South African wines

The objective of this study was to investigate the presence of genes coding for enzymes of oenological relevance in wine Lactobacillus strains isolated from South African grape and wine samples during the 2001 and 2002 harvest seasons. A total of 120 wine lactobacilli isolates belonging to Lactobacillus plantarum, Lactobacillus hilgardii, Lactobacillus brevis, Lactobacillus pentosus, Lactobacillus paracasei, Lactobacillus sakei and Lactobacillus paraplantarum were genetically screened for enzyme-encoding genes using PCR with primers specific for beta-glucosidase, protease, esterase, citrate lyase and phenolic acid decarboxylase. The results of PCR screening showed that the Lactobacillus strains possessed different combinations of enzymes and that some strains did not possess any of the enzymes tested. Confirmation analysis with gene sequencing also showed high similarity of genes with those available in GenBank database. In this study, we have demonstrated the existence of genes coding for wine-related enzymes in wine lactobacilli that could potentially hydrolyse wine precursors to positively influence wine aroma. An expansion of knowledge on the genetic diversity of wine-associated lactic acid bacteria will enable the selection of novel malolactic fermentation starter cultures with desired oenological traits for the improvement of the organoleptic quality of the wine, and hence wine aroma.

American Foreign Policy and the South African Grape Controversy

In the early 1930's and particularly between 1936–1938, the South African fruit and grape growers, with the unhidden blessing of the government, launched a series of diplomatic and non-diplomatic efforts to force the United States to let their wines into the American market. They eventually succeeded. This article examines this controversy as reflected in the Department of State's consular reports, cables and diplomatic exchanges of the period.

Saccharomyces capensis nov. spec.; a new yeast from South African grape must.

Saccharomyces capensis nov. spec.; a new yeast from South African grape must.