Chenin Blanc Grapes Research Articles

Screening Non-Saccharomyces Yeasts as Low Ethanol Producing Starter Cultures

Non-Saccharomyces yeasts are known for their low fermentation rate in comparison to Saccharomyces cerevisiae.  In this study, non-Saccharomyces yeasts were inoculated into Chenin blanc grape must and fermented under aerobic and anaerobic conditions.  Saccharomycodes ludwigii displayed a strain-dependent fermentation rate, which yielded between 5.2% and 9.9% ethanol concentration under both conditions, albeit with residual sugar.  Aerobic conditions favoured the production of reduced ethanol which was between 5.8% and 9.7% for non-Saccharomyces yeasts in comparison to S. cerevisiae (10%).  This trend was observed for Wickerhamomyces anomalus, Stamerella bacillaris (Candida zemplinina), Metshnikowia pulcherrima, Cyberlindnera saturnus, Wickerhamomyces subpelliculosus and Cyberlindnera jadinii.  The laboratory-scale wines prepared with the aforementioned yeasts yielded ripe fruit and floral aroma attributes while other non-Saccharomyces yeasts resulted in wines with spicy, acidic and solvent aroma notes.

Modeling grape quality by multivariate analysis of viticulture practices, soil and climate

Aims: The present study aims to model grape quality criteria by combining a large number of viticultural practices and soil and climatic variables related to the main determinants. Methods and results: A database has been developed using the Chenin blanc grape variety in a protected designation of origin. A statistical model, namely, a partial least squares (PLS) regression, was performed for each grape quality criterion (sugar content, total acidity, malic acid, tartaric acid, yeast available nitrogen, pH and bunch rot). This statistical analysis identified the main viticultural practices as well as soil and climate variables related to the grape quality at harvest. The results highlight the relationships between the vine pruning length (spur pruning = short pruning or cane pruning = long pruning) and pH and malic acid but also reveal even more significant relationships with tartaric acid, yeast available nitrogen and bunch rot. The dryness index and the plant density have a strong influence on the grape malic acid concentration and pH, respectively. Vine perennial practices are the greatest contributors to the grape the yeast available nitrogen concentration. Conclusion: The models note the most relevant viticultural practices and soil and climatic variables driving each studied grape quality criterion. Significance and impact of the study: The results provide a better understanding of the major variables influencing grape quality.

Modeling grape quality by multivariate analysis of viticulture practices, soil and climate

Aims. The present study aims to model grape quality criteria by combining a large number of viticultural practices and soil and climate variables related to the main determinants.Methods and results. A database has been developed using the Chenin Blanc grape variety in a Protected Designation of Origin. A statistical model, namely a Partial Least Squares (PLS) regression, has been determined for each grape quality criterion (sugar content, total acidity, malic acid, tartaric acid, available nitrogen, pH and bunch rot). This statistical analysis identifies the main viticultural practices and soil and climate variables related to the grape quality at harvest. The results highlight relationships between the length of vine pruning and pH and malic acid but even more significant relationships with tartaric acid, available nitrogen and bunch rot.Conclusion. The models point out the most relevant viticultural practices and soil and climate variables for the explanation of each grape quality criterion studied.Significance and impact of the study. The results provide a better understanding of the major variables that influence grape quality.

Chloroanisoles occurrence in wine from grapes subjected to electrolyzed water treatments in the vineyard

Recently the use of electrolyzed water (EW) attracted much attention as a high-performance, new technology for its potential use in the food industry. The aim of this work was to investigate the impact of grape EW treatments, applied at different time intervals prior to harvest, on the indigenous yeast populations of grape surface (Chenin blanc and Cabernet franc) and the occurrence of 2,4,6-trichloroanisole (TCA) in Cabernet franc wine. In addition, the evolution of inoculated and spontaneous fermentations on treated and non-treated grapes was also considered. The yeast population present on grape berries surface was influenced in a grape variety and EW treatment time-dependent way, since only Chenin blanc grapes treated with EW 7 days prior to harvest had significantly lower yeast population levels, compared to the respective control. Concerning the yeast diversity in the grape samples, a dominance of Aureobasidium pullulans was observed in treated grapes, independently of the grape variety. At the end of alcoholic fermentation, 2,4,6-trichloroanisole was detected in wine when the EW solution was applied at one or two weeks before harvest time. After wine storage, 2,4,6-trichloroanisole and chlorophenols contents generally exhibited a loss relative to initial values. The results showed that EW treatments tended to slightly increase the TCA concentration in final wine and did not affect the fermentation performances and chromatic properties of resulting wine. On the other hand, absorption or desorption phenomena by wine lees could be involved in the change of 2,4,6-trichloroanisole concentration in wine during storage time.

Wine chemical, sensory, aroma compound and protein analysis of wines produced from chemical and biological fungicide treated Chenin blanc grapes

Fungal diseases in vineyards are one of the main causes leading to economic losses within the viticulture sector and are continuously increasing with time. The most common of these fungal diseases are powdery mildew, downy mildew and grey mould which are controlled by the use of fungicides. However, fungicide residues can alter the fermentation process and prevent some biochemical pathways of yeast metabolism involved in phenolic and/or aroma compound production that are critical for sensory quality. In this study, Chenin blanc grapes treated with chemical and natural fungicides were used to produce small-scale wines and laboratory-scale fermentations. Treatments consisted of a control (an approved chemical used in industry), a 1x and 2x treatment (new formulations). Laboratory-scale fermentations were conducted in duplicate using the commercial Saccharomyces cerevisiae (S. cerevisiae) Active Dry Wine Yeast (ADWY) strains VIN 13 and VIN 7. The fermentations were monitored by weighing frequently until they stabilised (CO2 weight loss). Small-scale wines were made according to the standard Nietvoorbij experimental wine making procedure. At the end of fermentation, lees samples were subjected to CHEF gel electrophoreses to confirm that the inoculated yeast strain completed the fermentations. Moreover, fermenting wine samples, collected at the start and end of the fermentation, were subjected to protein extraction, quantification and characterisation the yeast proteins expressed at the various stages of fermentation. Resultant wines were subject to chemical and sensory evaluations five months after bottling. From the results obtained in the above study, it was concluded that the inoculated yeast strains used for wine making completed the fermentations at a similar rate to their respective controls (registered fungicide). In addition, small-scale cellar fermentations showed that the fungicide treatments (1x the recommended dosage [Treatment 1] and 2x the recommended dosage [Treatment 2]) compared to the controls had no notable negative effects on wine aroma and sensory profiles although differences were observed in the proteins expressed after the fermentation. The chemical and biological fungicides had no notable effects on the wine making procedure and quality of resulting wines compared to the registered fungicide.

Inter-annual variability in the environmental performance of viticulture technical management routes—a case study in the Middle Loire Valley (France)

Improving the environmental performances of viticulture practices is particularly complicated during unfavorable climatic conditions because of the need for fungal and other pest pressure and the variability of phytosanitary control methods available for winegrowers. However, winegrowers wish to improve the environmental performances of their practices regardless of climatic conditions. The objective of the study was to quantify the variability in environmental impacts due to climatic variations, and changes in viticulture practices induced by climatic variability. Life cycle assessment was used to evaluate the environmental impacts of viticulture technical management routes (TMR) implemented on five plots in the Loire Valley for the Chenin Blanc grape variety. These TMRs are representative of the range of practices used in the region, including intensive conventional practices to moderate organic practices. The study covered two different years of production (2011 and 2013) under contrasting climatic conditions. The first year (2011) was hot and dry, which are favorable conditions for viticulture, while the second year (2013) was cold and humid, which are unfavorable conditions. During the unfavorable year, the number of phytosanitary treatments and soil maintenance interventions increased for most of the studied TMRs. This meant that the inter-annual variability in environmental impact was significant, depending on the type of TMR, with differences in impacts ranging from 19% to more than 40% between 2011 and 2013. Managing environmental impacts was found to be more difficult for the organic systems when climatic conditions are unfavorable (in 2013). The non-organic TMRs showed less variation in environmental impacts than the organic TMRs between the 2 years studied. This study shows the importance of taking into account inter-annual variability in environmental assessments of viticulture systems. Indeed, winegrowers do not respond the same way to climate variability mainly with regard to plant protection and soil maintenance. Viticulture is very sensitive to inter-annual climate variations due to the parasitic pressure variability. The different production systems do not give to winegrowers the same possibilities for adapting practices to limit their impact on the environment.

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.

Effect of Sunlight and Shade on N orisoprenoid Levels in Maturing Weisser Riesling and Chenin blanc Grapes and Weisser Riesling Wines

The effect of sunlight, shade and degree of ripeness on potentially volatile C13-norisoprenoid concentrations in Weisser Riesling grapes and wines and in Chenin blanc grapes, was investigated. Norisoprenoids were released from their bound forms by acid and enzymatic hydrolysis. With few exceptions, norisoprenoid concentrations were significantly higher in sun-exposed grapes than in shaded grapes. Significant increases in norisoprenoid concentrations were observed with an increase in ripeness. Microclimatic conditions during grape ripening for the production of Weisser Riesling wine with a potential to form lower concentrations of TDN during ageing are proposed.

Occurrence and Detection of Killer Yeasts on Chenin Blanc Grapes and Grape Skins

Two hundred and thirty killer yeast strains were selectively isolated from Chenin blanc grapes and grape skins collected from six wineries. The killer yeasts were divided into nine groups based on their colony morphology and colour on modified Wallerstein laboratory nutrient agar. All strains fermented Chenin blanc grape must (pH 3,5; 40 mg/ I free SO, and 5% (v/v) ethanol) at l4°C. Existing techniques in which methylene blue are used were evaluated to detect killer yeasts, to determine interactions between different killer phenotypes, and to determine the sensitivity of commercial strains to the killer toxins.

Carotenoid Levels in Maturing Grapes as Affected by Climatic Regions, Sunlight and Shade

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.

Characterization of Killer Yeast Isolates from Chenin blanc Grapes and Grape Skins

Wild-type killer yeast strains isolated from six South African wineries were identified using classical taxonomic methods. They were further characterized according to their cross-reactions with reference killer yeasts (K1-Kn) and by electrophoresis of their double-stranded RNA molecules. All isolates belonged to the K2 phenotype and were identified as strains of Saccharomyces cerevisiae and Saccharomyces bayanus. The killer strains differed substantially in their ability to kill a sensitive wine yeast (Geisenheim GS-1). This phenomenon may be attributed to strain differences among the killer yeasts as was shown by electrophoresis of total soluble cell proteins and gas chromatographic analysis of cellular fatty acids.

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 veraison. 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 veraison. 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 veraison were lower than in grapes that were irrigated at pea size. Irrigation applied 21 days and 28 days after veraison resulted in higher total titratable acidity in the juice of both cultivars. Irrigation applied 31 days after veraison, 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.

English

The aim of this study was to evaluate the effect of indigenous yeasts on the aroma of  fermented Chenin Blanc grape must by determining the volatile compounds, the odor activity value (OAV) and carrying out sensory analyses. The must, fermented by Hanseniaspora opuntiae/Saccharomyces cerevisiae combinations, presented higher concentrations of compounds such as ethyl acetate, ethyl hexanoate, 2-methyl-1-propanol and 2-phenylethanol, and a lower production of acids and acetaldehyde. This fermented must presented higher OAV values for compounds such as 2-methyl-1-propanol and ethyl acetate, 687.06 and 1264.16, respectively. 2-phenylethanol was produced by H. opuntiae and Hanseniaspora guilliermondii in combination with S. cerevisiae in amounts that resulted in OAV values of 5.63 and 4.62, respectively. In appropriate concentrations, these volatile compounds contribute positively to the aromatic quality of the fermented must. The highest mean acceptability and purchasing intention scores were obtained by the must fermented by H. opuntiae/S. cerevisiae. In the must fermented by H. guilliermondii/ S. cerevisiae, the absence of ethyl hexanoate and high concentrations of octanoic acid and acetaldehyde probably contributed to its low acceptability. Thus, it was suggested that the yeast genus Hanseniaspora in combination with S. cerevisiae, showed the potential to positively impact the wine aroma.   Key words: Non-Saccharomyces yeasts, volatile compounds, odor activity value, acceptability test, Hanseniaspora, “São Francisco Valley region”.

The effect of mechanical harvesting on wines of Chenin blanc grapes in South Africa

Alternate rows of a Chenin blanc test vineyard in its 9th leaf on the experimental farm of the Oenological and Viticultural Research Institute, Stellenbosch, were harvested by hand and machine. The effects of harvesting temperature, MOG content and holding time of mechanically-harvested grapes on wine quality were evaluated; these wines were compared with wines from hand-harvested grapes. Results showed that increases in the MOG content, harvesting temperature and holding time singly or cumulatively caused an increase in the total polyphenols of the wines. Similarly, increases in MOG content, harvesting temperature and holding time were deleterious to wine quality and the effects were cumulative. Furthermore, a holding time of up to 4 h brought about no significant decrease in wine quality, provided the grapes were harvested at low temperatures. When grapes were harvested at high temperatures, the holding time had to be reduced to 3 h with a low MOG content in order to produce wines of similar quality. With high MOG content the quality significantly lower even with a holding time of only 1 h. Der Einflus der maschinellen Traubenernte auf den Wein der Sorte Chenin blanc in Sudafrika In einem Versuchsweinberg des Oenological and Viticultural Research Institute, Stellenbosch, wurden die Rebzeilen abwechselnd maschinell und von Hand gelesen. Der Einflus der Lesetemperatur, der Wartezeit der Trauben zwischen Lese und Weinbereitung sowie der Verunreinigung (MOG) des maschinell geernteten Lesegutes auf die Weinqualitat wurde untersucht; die so gewonnenen Weine wurden mit Weinen aus handgelesenen Trauben verglichen. Es zeigte sich, das bei einer Steigerung von Lesetemperatur, Wartezeit der Trauben und MOG-Anteil der Gesamtpolyphenolgehalt in den Weinen zunahm. Diese Faktoren wirkten sich auch auf diesensorisch ermittelte Weinqualitat nachteilig aus. Bei einer Wartezeit bis zu 4 h war bei niedrigem oder hohem MOG-Anteil kein ungunstiger Einflus auf die Weinqualitat nachweisbar, vorausgesetzt, das die Trauben bei niedriger Temperatur gelesen wurden. Um bei hoheren Lesetemperaturen Weine ahnlich guter Qualitat zu erzielen, durfte die Wartezeit 3 h nicht uberschreiten und muste der MOG-Anteil niedrig sein. Bei hohem MOG-Anteil war die Weinqualitat dagegen betrachtlich verringert, auch wenn die Wartezeit nur 1 h betrug.

Physico-chemical properties of botrytised Chenin blanc grapes to assess the extent of noble rot

The production of botrytised wines involves grapes with high sugar concentration and complex aromas caused by the presence of noble rot. The aim of this paper was to characterise botrytised grapes on a physico-chemical basis and therefore identify markers of its evolution. Colour analysis, compression and puncture tests and phenolic profiles were performed in order to identify the potential markers and discriminating tools for the presence of the fungus. Chenin blanc grapes from two parcels in Loire Valley (France) were sampled during a 4-week period. Significant changes of phenolic composition like the total polyphenol which decreases up to 40 % were observed as B. cinerea was more advanced on the berries. Myricetin a compound that has not been reported before in white grapes was found only in highly affected berries. At the same time as the level of infection increases, the presence of the fungus seems to induce, from one side, an increase of catechin, epicatechin and epicatechin gallate, and from the other side, the decrease in caftaric acid, coutaric acid, quercetin-3 glucoside and kaempferol-3 glucoside. Puncture tests appeared to be the more reliable mechanical tool to differentiate between infection levels by itself; however, the combination of puncture and compression tests with colour showed a more significant and clear differentiation. This combination appeared to be the most adequate for stablish markers of noble rot evolution in the conditions studied. A decrease in mechanical resistance of berries’ skin (measured by the maximum puncture force required for skin rupture) was observed during infection. These results on botrytised Chenin grapes are new and provide a novel approach for an objective measurement of noble rot in Chenin grapes.

Impact of a Non-<i>Saccharomyces</i> Yeast Isolated in the Equatorial Region in the Acceptance of Wine Aroma

The aim of this work was to isolate and identify the yeasts prevalent in fresh grapes cultivated in the “São Francisco Valley” region (Brazil), as well as evaluating the cell growth of these indigenous yeasts during the fermentation of grape musts and their contribution to the improvement of wine aroma. The Chenin Blanc grape must fermented by H. opuntiae presented higher acceptance means at the three points analyzed (6.74, 6.78 and 7.30) and in the fermentation carried out by the yeasts H. opuntiae and S. cerevisiae, the highest mean acceptance (7.22) was observed after 120 hours, with no statistical difference from the sample fermented by H. opuntiae alone. Since these samples that showed higher acceptance means also receiving higher scores for purchasing intention, corresponding to the concepts of “definitely would buy” and “probably would buy”. The present study suggests that the fermentations of grape musts carried out by the yeast H. opuntiae and mixed cultures of H. opuntiae and Saccharomyces cerevisiae, positively influenced the sensory qualities of the wines and showed greater potential to increase the aroma of the musts and to develop specific wine styles.

Malo‐ethanolic fermentation in grape must by recombinant strains of Saccharomyces cerevisiae

Recombinant strains of Saccharomyces cerevisiae with the ability to reduce wine acidity could have a significant influence on the future production of quality wines, especially in cool climate regions. L-Malic acid and L-tartaric acid contribute largely to the acid content of grapes and wine. The wine yeast S. cerevisiae is unable to effectively degrade L-malic acid, whereas the fission yeast Schizosaccharomyces pombe efficiently degrades high concentrations of L-malic acid by means of a malo-ethanolic fermentation. However, strains of Sz. pombe are not suitable for vinification due to the production of undesirable off-flavours. Heterologous expression of the Sz. pombe malate permease (mae1) and malic enzyme (mae2) genes on plasmids in S. cerevisiae resulted in a recombinant strain of S. cerevisiae that efficiently degraded up to 8 g/l L-malic acid in synthetic grape must and 6.75 g/l L-malic acid in Chardonnay grape must. Furthermore, a strain of S. cerevisiae containing the mae1 and mae2 genes integrated in the genome efficiently degraded 5 g/l of L-malic acid in synthetic and Chenin Blanc grape musts. Furthermore, the malo-alcoholic strains produced higher levels of ethanol during fermentation, which is important for the production of distilled beverages.

Aroma Components of Vitis vinifera L. cv. Chenin blanc Grapes and Their Changes During Maturation

Samples of Chenin blanc grapes from 3 localities and at various stages of maturity were harvested over a period of 11 weeks. The freon extracted aroma components were subjected to gas chromatographic and coupled gas chromatographic-mass spectrometric analyses. No measureable amounts ofterpenoid components were detected in any of the samples. Two isomers of 2,4-decadienal, a novel component in Vitis vinifera L. cultivars, occurred in relatively large concentrations in all samples. Origin of sample and degree of maturity have an insignificant effect on the concentration of selected aroma components.