SciCombinator

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Concept: Sauvignon blanc

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Sauvignon blanc wines are produced under a wide variety of winemaking conditions, some of which include different fruit-ripening levels, cold soaks and the use of fining agents and inert gases. Anecdotal evidence suggests that sensory variations among these wines may have to do with their phenolic composition and concentration. Therefore the aim of this work was to study the effects of different winemaking conditions typically used in Chile on the phenolic composition and concentration of Sauvignon blanc wines.

Concepts: Oenology, Fermentation, Noble gas, Gases, Cabernet Sauvignon, Sauvignon blanc, Chardonnay, Chilean wine

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In order to investigate the effects of cryomaceration and reductive vinification on chemical and physical indices and on antioxidant compounds of Sauvignon blanc wines, four wine-making procedures were applied: traditional white vinification, skin cryomaceration, vinification in a reductive environment, and a combination of the last two procedures. Significant differences were highlighted by both conventional analyses and NMR spectroscopy. The strongest changes were for organic acid concentrations (tartaric, in particular) and phenolic content. Cryomaceration caused a strong precipitation of tartaric acid, which may be desired if grapes have high acidity values. Cryomaceration protected those flavans reactive with vanillin from the action of oxidative enzymes. Vinification in a reductive environment, alone or combined with a cryomaceration step, gave wines with the highest solids content and caused a greater extraction of phenolic compounds from skins compared to traditional winemaking or cryomaceration alone, due to SO(2) solubilisation. Grape oenological expression can be strongly affected by the application of the investigated wine-making procedures.

Concepts: Yeast, Vitis vinifera, Wine, Oenology, Fermentation, Winemaking, Sauvignon blanc, Potassium bitartrate

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There has been increasing interest in the use of selected non-Saccharomyces yeasts in co-culture with Saccharomyces cerevisiae. The main reason is that the multistarter fermentation process is thought to simulate indigenous fermentation, thus increasing wine aroma complexity while avoiding the risks linked to natural fermentation. However, multistarter fermentation is characterised by complex and largely unknown interactions between yeasts. Consequently the resulting wine quality is rather unpredictable. In order to better understand the interactions that take place between non-Saccharomyces and Saccharomyces yeasts during alcoholic fermentation, we analysed the volatile profiles of several mono-culture and co-cultures. Candida zemplinina, Torulaspora delbrueckii and Metschnikowia pulcherrima were used to conduct fermentations either in mono-culture or in co-culture with S. cerevisiae. Up to 48 volatile compounds belonging to different chemical families were quantified. For the first time, we show that C. zemplinina is a strong producer of terpenes and lactones. We demonstrate by means of multivariate analysis that different interactions exist between the co-cultures studied. We observed a synergistic effect on aromatic compound production when M. pulcherrima was in co-culture with S. cerevisiae. However a negative interaction was observed between C. zemplinina and S. cerevisiae, which resulted in a decrease in terpene and lactone content. These interactions are independent of biomass production. The aromatic profiles of T. delbrueckii and S. cerevisiae in mono-culture and in co-culture are very close, and are biomass-dependent, reflecting a neutral interaction. This study reveals that a whole family of compounds could be altered by such interactions. These results suggest that the entire metabolic pathway is affected by these interactions.

Concepts: Yeast, Saccharomyces cerevisiae, Saccharomyces pastorianus, Brewing, Yeasts, Saccharomycetes, Saccharomycetaceae, Sauvignon blanc

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The evolution of the varietal thiol 3-mercaptohexanol acetate (3MHA) and other key aroma compounds has been monitored in New Zealand Sauvignon blanc wines stored for 1 year at three different temperatures (5, 10 and 18 °C). The main processes that occurred in the Sauvignon blanc wines during bottle ageing were hydrolysis of 3MHA and other acetate esters, hydrolysis of ethyl esters of fatty acids, and the formation of ethyl esters of branched acids. The kinetic parameters of ester hydrolysis, including reaction rate constants and activation energies, were determined, which allow prediction of future wine composition based upon storage temperature and time. It was found that 3MHA had the highest reaction rate constant, meaning that this compound is the most unstable, particularly at higher storage temperatures, and that it disappeared very fast during wine storage.

Concepts: Fatty acid, Ester, Reaction rate constant, Wine, Fermentation, Cabernet Sauvignon, Sauvignon blanc, Chardonnay

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New Zealand Sauvignon blanc (SB) wines are characterised by a distinctive combination of tropical-fruity and green-herbaceous aromatic compounds. The influence of sunlight exposure of grape clusters on juice and wine composition was investigated, with the aim of manipulating aromatic compounds in SB wine. In the absence of basal leaf removal SB clusters naturally exposed to sunlight were riper than shaded clusters, evidenced by higher total soluble solids (TSS) and proline, and lower malic acid, 3-isobutyl-2-methoxypyrazine (IBMP) and arginine. Volatile thiols in wines did not differ between shaded and exposed clusters. At equivalent TSS, cluster exposure had little or no effect on malic acid concentration. Conversely, wine from shaded clusters had almost double the IBMP concentration of wine from exposed clusters at equivalent TSS. The effects on SB juice and wine composition of natural variations in cluster microclimate are not comparable with the effects of cluster exposure created through leaf removal.

Concepts: Vitis vinifera, Wine, Fermentation, Cabernet Sauvignon, Sauvignon blanc, Chardonnay, Bordeaux, Chilean wine

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In the wine industry, fining agents are commonly used with many choices now commercially available. Here the influence of pre-fermentation fining on wine aroma chemistry has been explored. Free run and press fraction Sauvignon blanc juices from two vineyards were fined using gelatin, activated carbon, polyvinylpolypyrrolidone (PVPP) and a combination agent which included bentonite, PVPP and isinglass. Over thirty aroma compounds were quantified in the experimental wines. Results showed that activated carbon fining led to a significant (p<0.05) concentration decrease of hexan-1-ol and linalool in the experimental wines when compared to a control, consistent across all vineyard and fraction combinations. Other aroma compounds were also influenced by fining agent, even if vineyards and press fractions played a crucial role. This study confirmed that fining agents used pre-fermentation can influence wine aroma profiles and therefore needs specific tailoring addressing style and origin of grape.

Concepts: Brewing, Oenology, Fermentation, Oak, Sauvignon blanc, Bordeaux, Isinglass, Finings

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Grape pomace is a winemaking by-product that can be used to extract oenological tannins. Recently, some grape skin tannins were shown to contain very high amounts of two polyfunctional thiol precursors (3-S-glutathionylhexan-1-ol, 3-S-cysteinylhexan-1-ol) whose free forms are responsible for appreciated tropical-like flavours. This study shows that an oxidative treatment (no SO2) of white grape pomace and the presence of grape leaves and stems can increase the content of the above mentioned precursors. Moreover, it shows significant differences between Sauvignon Blanc, Gewuerztraminer and Mueller-Thurgau grape pomace for the 3-mercaptohexan-1-ol precursors and 4-S-cysteinyl-4-methylpentan-2-one. The grape cultivar is crucial, but the technological ability of enhancing the level of the volatile thiol precursors simply by treating the grape marc in different ways is a promising and powerful tool for the production of potentially flavouring tannins intended for food and beverage industry.

Concepts: Cabernet Sauvignon, Grape varieties, Sauvignon blanc, Pomace, Grape seed oil

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This study investigated the potential to improve wine aroma by applying two inactive dry yeast products (IDYs) at the onset of ripening on Sauvignon Blanc grapes. Both products led to increased reduced glutathione concentrations in the grape juice and corresponding wines, as well as differences in individual higher alcohol acetates (HAAs) and ethyl esters of straight chain fatty acids (EEFAs) at the end of fermentation. After two months of storage, a significantly slower decrease of EEFAs and to a lesser extent of HAAs was found for wines made from grapes with IDY applications. These wines also resulted in significantly slower synthesis of ethyl esters of branched acids, whereas varietal thiols were altered in a product-specific manner. The modifications in the wine chemical composition were also sensorially corroborated. This study showed that vineyard additions of IDY products directly on the grapes at the onset of ripening have a subsequent benefit to the production and preservation of aroma in wines.

Concepts: Alcohol, Ethanol, Yeast, Wine, Fermentation, Cabernet Sauvignon, Sauvignon blanc, Chardonnay

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Sauvignon blanc wine, balanced by herbaceous and tropical aromas, is fermented at low temperatures (10-15 °C). Anecdotal accounts from winemakers suggest that cold ferments produce and retain more ‘fruity’ aroma compounds; nonetheless, studies have not confirmed why low temperatures are optimal for Sauvignon blanc. Thirty-two aroma compounds were quantitated from two Marlborough Sauvignon blanc juices fermented at 12.5 °C and 25 °C, using Saccharomyces cerevisiae strains EC1118, L-1528, M2 and X5. Fourteen compounds were responsible for driving differences in aroma chemistry. The 12.5 °C-fermented wines had lower 3-mercaptohexan-1-ol (3MH) and higher alcohols, but increased fruity acetate esters. However, a sensory panel did not find a significant difference between fruitiness in 75 % of wine pairs based on fermentation temperature, in spite of chemical differences. For wine pairs with significant differences (25 %), the 25 °C-fermented wines were fruitier than the 12.5 °C-fermented wines, with high fruitiness associated with 3MH. We propose that the benefits of low fermentation temperatures are not derived from increased fruitiness, but a better balance between fruitiness and greenness. Even so, since 75 % of wines showed no significant difference, higher fermentation temperatures could be utilized without detriment, lowering costs for the wine industry.

Concepts: Yeast, Saccharomyces cerevisiae, Wine, Alcoholic beverage, Fermentation, Winemaking, Sauvignon blanc, Chardonnay

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Elemental sulfur is a fungicide traditionally used to control Powdery Mildew in the production of grapes. The presence of sulfur residues in grape juice has been associated with increased production of hydrogen sulfide during fermentation, which could take part in the formation of the varietal thiol 3-mercaptohexanol. This work examines whether elemental sulfur additions to Sauvignon blanc juice can increase the levels of sought-after varietal thiols. Initial trials were performed in South Africa and indicated a positive impact of sulfur on the levels of thiols. Further experiments were then carried out with New Zealand Sauvignon blanc and confirmed a positive relationship between elemental sulfur additions and wine varietal thiols. The formation of hydrogen sulfide was observed when the addition of elemental sulfur was made to clarified juice, along with an increase in further reductive sulfur compounds. When the addition of sulfur was made to pressed juice, prior to clarification, the production of reductive sulfur compounds was drastically decreased. Some mechanistic considerations are also presented, involving the reduction of sulfur to hydrogen sulfide prior to fermentation.

Concepts: Sulfur, Hydrogen sulfide, Wine, Fermentation, Thiol, Cabernet Sauvignon, Sauvignon blanc, Chardonnay