Biochemical changes throughout grape berry development and fruit and wine quality

Wine is made up of more than one thousand compounds, the majority of which, such as vitamins and minerals, come from the grapes, while others, like ethanol and glycerol, are products of the winemaking process. Although sugars are either partially or completely transformed, sugar import and accumulation into the ripening berry is a major parameter of wine quality. Sugar status is directly related to the final alcoholic content of wine, and regulates several genes responsible for the development of its aromatic and organoleptic properties. Physiological ripeness is reached when the grapes achieve sufficiently high sugar levels without loosing too much acidity; however, aromatic and phenolic compound content must also be taken into account. Softening and water content are other essential characteristics of a ripe berry. From a winemaker point of view, optimal grape maturity is essential for wine quality, but is difficult to assess because it is under multifactorial control, involving grapevine cultivar variety and environmental parameters such as soil, temperature, exposure to sun, and hormonal regulation. Continued study of the key control points in grape ripening is crucial if we ultimately hope to improve grape and wine quality.Fundação para a Ciência e a Tecnologia (FCT)(research project ref. POCI/AGR/56378/2004; to C.C., grant ref. SFRH/BD/10689/2002, to P.S. grant ref. SFRH/BD/13460/2003, to N.F. grant ref. SFRH/BD/23169/2005, and to A.A., grant ref. SFRH/PBD/17166/2004

Sauvignon Blanc Wine: Contribution of Ageing and Oxygen on Aromatic and Non-aromatic Compounds and Sensory Composition : A Review

Oxidation and the capacity for sufficient ageing potential of white wines are constant problems forwinemakers worldwide. In general, it is accepted that certain grape varieties are especially sensitive tooxidation, suggesting that some of the chemical components key to their sensory attributes are stronglymodulated by oxygen exposure. Sauvignon blanc is a well-documented example of an oxygen-sensitivewine, and understanding the stability of various compounds is crucial in order to preserve the fresh andfruity characters of Sauvignon blanc wines while preventing the formation of off-odours over a longperiod of time. Compounds such as the volatile thiols and methoxypyrazines are key aroma compoundsresponsible for the typical Sauvignon blanc aroma, while other aroma compounds, such as esters, alcoholsand acids, can also contribute to the wine aroma. Oxidation-related compounds (such as aldehydes) canoccur under certain conditions and it is essential to understand the chemistry behind oxidation to controland manage the development of various characteristics in wine. The sensory interactions occurringbetween various compounds (both aromatic and non-aromatic) are also important due to enhancing orsuppressive effects that can mask certain aroma nuances. This review focuses on the stability of certaincompounds of Sauvignon blanc wines during oxidation and ageing and how it affects the aromatic andnon-aromatic composition of these wines

Sauvignon blanc wine : contribution of ageing and oxygen on aromatic and non-aromatic compounds and sensory composition : a review

CITATION: Coetzee, C. & Du Toit, W. J. 2015. Sauvignon blanc wine : contribution of ageing and oxygen on aromatic and non-aromatic compounds and sensory composition : a review. South African Journal for Enology and Viticulture, 36(3):347-365, doi:10.21548/36-3-968.The original publication is available at http://www.journals.ac.za/index.php/sajevOxidation and the capacity for sufficient ageing potential of white wines are constant problems for winemakers worldwide. In general, it is accepted that certain grape varieties are especially sensitive to oxidation, suggesting that some of the chemical components key to their sensory attributes are strongly modulated by oxygen exposure. Sauvignon blanc is a well-documented example of an oxygen-sensitive wine, and understanding the stability of various compounds is crucial in order to preserve the fresh and fruity characters of Sauvignon blanc wines while preventing the formation of off-odours over a long period of time. Compounds such as the volatile thiols and methoxypyrazines are key aroma compounds responsible for the typical Sauvignon blanc aroma, while other aroma compounds, such as esters, alcohols and acids, can also contribute to the wine aroma. Oxidation-related compounds (such as aldehydes) can occur under certain conditions and it is essential to understand the chemistry behind oxidation to control and manage the development of various characteristics in wine. The sensory interactions occurring between various compounds (both aromatic and non-aromatic) are also important due to enhancing or suppressive effects that can mask certain aroma nuances. This review focuses on the stability of certain compounds of Sauvignon blanc wines during oxidation and ageing and how it affects the aromatic and non-aromatic composition of these wines.http://www.journals.ac.za/index.php/sajev/article/view/968Publisher's versio

Varietal aromas of Sauvignon Blanc: Impact of oxidation and antioxidants used in winemaking

Key varietal characteristics of Sauvignon Blanc, including the descriptors of ‘green’ and ‘tropical fruit’, are mostly attributed to methoxypyrazines and volatile thiols, while monoterpenes, higher alcohols, esters, fatty acids, and other volatile compounds also add complexity and fruity notes to the wines. During the winemaking and ageing period, oxidation decreases the concentrations of these compounds and diminishes the flavours derived from this aromatic grape variety. Therefore, antioxidants, such as sulfur dioxide, are commonly utilized in Sauvignon Blanc wine production for better preservation of those beneficial primary aromas. This review focuses on key varietal aromas in Sauvignon Blanc wine and how they are influenced by oxidation, and SO₂ alternatives, including ascorbic acid, glutathione, and glutathione-enriched inactivated dry yeasts, that can be used in winemaking as antioxidants

Aroma Compounds in Wine

Volatile aroma compounds are very important to grape wine quality. In order to understand the flavor of wine, a multitude of scientific investigations was carried out and a number of appropriate analytical tools for flavor study were developed in the past few decades. This chapter deals with major achievements reported in wine aroma and flavor. Firstly, we illustrate the existing knowledge on aroma compounds contributing to wine flavor, as well as the types of wine aroma compounds. Furthermore, the main factors affecting flavor quality in wine are discussed. Finally, the genomics and biotechnology of wine flavor are also summarized. This chapter broadens the discussion of wine aroma compounds to include more modern concepts of biotechnology and also provides relevant background and offers directions for future study

Oxygen and sulphur dioxide additions to Sauvignon blanc : effect on must and wine composition

Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2011.Includes bibliogaphy.ENGLISH ABSTRACT: Sauvignon blanc wines have become increasingly popular in South Africa as it is a cultivar that can be easily manipulated in the vineyard and cellar to produce a range of wine styles. These wines are usually given aroma descriptors such as green pepper, grassy and asparagus; while other more tropical aromas include passion fruit and guava. These aromas are thought to be mainly caused by methoxypyrazines and volatile thiols. These compounds are known to be character impacting compounds of Sauvignon blanc and are present in the grapes in the aromatic form (methoxypyrazines) or as non‐aromatic precursors (thiols) that can be released by the yeast during fermentation. Other aroma compounds such as esters, higher alcohols, fatty acids and monoterpenes are compounds that could potentially influence the aroma bouquet of a wine significantly. These aroma compounds exist either as precursors in the grapes (monoterpenes) or arise due to yeast metabolism during fermentation (esters, higher alcohols, fatty acids) and often display fruity, floral and pleasant aromas. In the cellar, winemaking practices can be manipulated to a certain extent to achieve the desired wine style. Winemaking tools such as temperature, skin contact, pressing conditions, oxygen (O2), sulphur dioxide (SO2) and yeast strain are only a few factors influencing the outcome of a wine. In general, South African winemakers maintain a very reductive environment during Sauvignon blanc wine production by using inert gasses, thereby causing the production costs to increase. There is sufficient evidence to support the reductive handling of white wine, however there seems to be a lack of information as to why the must should be treated reductively before fermentation. The over all goal of this study was thus to investigate the effect of different O2 and SO2 additions to Sauvignon blanc must before settling, specifically focussing on the typical aroma compounds often found in these wines. Chapter 2 gives an overview of the oxidation reactions occurring in must (enzymatic oxidation) and wine (chemical oxidation). This chapter also reports the origin of the specific Sauvignon blanc aroma compounds and their reaction to different must and wine treatments with a focus on oxidation. Chapter 3 reports research results focussing on the effect of the different must treatments on the character impacting compounds of Sauvignon blanc wines, specifically the methoxypyrazines and the volatile thiols. The effect of the treatments on the polyphenols and glutathione content in the must and wine was also investigated. Oxidation in the absence of SO2 led to a decrease in glutathione and certain phenolic compounds in the must. In general, volatile thiols were protected against oxidation by SO2, even when O2 was present in the must. Methoxypyrazines concentrations were not significantly influenced by the treatments. Chapter 4 elucidates the effect of the treatments on other yeast and grape derived aroma compounds often found in Sauvignon blanc wines, such as the esters, higher alcohols, fatty acids and monoterpenes. In general, the effect of SO2 seemed to have the greatest influence on the produced aroma compounds. The results reported in this thesis could possibly change the way South African Sauvignon blanc musts are handled in future during the winemaking process. It is clear that O2 and SO2 management in the cellar is of critical importance for the winemaker to produce wines of high quality. Future work is important to fully understand the mechanisms and evolution of important aroma compounds of Sauvignon blanc wines during the winemaking process.AFRIKAANSE OPSOMMING: Sauvignon blanc wyn aroma word gewoonlik beskryf met terme soos groen rissie, grasagtig en aspersie terwyl ander tropiese aromas soos grenadella en koejawel ook dikwels voorkom. Die manipulasie van Sauvignon blanc in die wingerd en in die kelder tydens wynmaak, gee die wynprodusent die vryheid om ‘n wye reeks wyn style te produseer. Dit maak Sauvignon blanc baie populêr in die Suid‐Afrikaanse wynindustrie. Die bogenoemde aromas word waargeneem in die wyn as gevolg van die teenwoordigheid van sekere aroma komponente genaamd metoksipirasiene en vlugtige tiole. Hierdie komponente lewer ‘n unieke bydrae tot die aroma samestelling van Sauvignon blanc wyne en kom voor in die druiwe in die aromatiese vorm (metoksipirasiene) of as nie‐aromatiese voorlopers (tiole) wat tydens alkoholiese fermentasie deur die gis vrygestel kan word. Komponente soos esters, hoër alkohole, vetsure en monoterpene kan ook ‘n potensiële bydra lewer tot die algehele aroma van Sauvignon blanc wyne en kom voor in die druiwe (monoterpene) of ontstaan as gevolg van gis metabolisme gedurende alkoholiese fermentasie (esters, hoër alkohole, vetsure). Hierdie geur komponente word dikwels beskryf as vrugtig, blomagtig en oor die algemeen aangenaam. Tydens wynmaak kan die wyn tot ‘n mate gemanipuleer word om ‘n spesifieke wynstyl te bekom. Hulpmiddels soos temperatuur, dopkontak, pers omstandighede, suurstof (O2), swawel dioksied (SO2) en gisras is slegs ‘n paar faktore wat die algemene uitkoms van ‘n wyn kan beïnvloed. Oor die algemeen word Sauvignon blanc in Suid‐Afrika baie reduktief behandel tydens wynbereiding. Dit vereis sekere hulpmiddels, soos die gebruik van inerte gas, wat die produksiekoste dikwels verhoog. Navorsing ondersteun die reduktiewe behandeling van wit wyn, maar dit wil voorkom asof daar ‘n tekort aan navorsing is wat die reduktiewe behandeling van die sap voor fermentasie regverdig. Die algemene doel van die studie is dus om die effek van verskillende O2 en SO2 byvoegings tot Sauvignon blanc sap (voor afsak) te ondersoek met die fokus op die tipiese aroma komponente wat in die wyn voorkom. Hoofstuk 2 lewer ‘n algemene oorsig van die tipes oksidasie reaksies wat voorkom in sap (ensiematiese oksidasie) en wyn (chemiese oksidasie). Spesifieke Sauvignon blanc aroma komponente word ook ondersoek in terme van die oorsprong van die komponente asook die reaksie wat plaasvind met verskillende mos en wyn behandelings, met ‘n fokus op oksidasie. In hoofstuk 3 word die effek van die verskillende mos behandelings op tipiese Sauvignon blanc aroma komponente, spesifiek metoksipirasiene en vlugtige tiole, ondersoek. Die effek van die behandelings op die polifenole en glutatioon inhoud in die mos en wyn word ook gerapporteer. Oksidasie van die sap in die afwesigheid van SO2, het ‘n afname in glutatioon en sekere polifenol konsentrasies veroorsaak. Dit wil voorkom asof die produksie van vlugtige tiole oor die algemeen beskerm word teen oksidasie indien daar genoegsame SO2 teenwoordig is. Hierdie effek word ondervind selfs as die sap met suursof versadig word. Die effek van die behandelings op die konsentrasies van metoksipirasiene was nie beduidend nie. Hoofstuk 4 rapporteer die effek van die behandelings op ander aroma komponente soos esters, hoër alkohole, vetsure en monoterpene. Oor die algemeen wil dit voorkom asof die effek van SO2 beduidend was en waarskynlik die grootste invloed op die produksie van hierdie aroma komponente het. Na aanleiding van die resultate bevind in hierdie tesis, is daar ‘n moontlikheid dat die manier waarop Sauvignon blanc wyne geproduseer word in Suid‐Afrika, moontlik kan verander in die toekoms. Vir die wynmaker om hoë kwaliteit Sauvignon blanc wyne te produseer, is O2 en SO2 bestuur in die kelder van kardinale belang. Verdere navorsing moet steeds gedoen word om die meganisme en evolusie van belangrike aroma komponente in Sauvignon blanc wyne tydens die wynmaakproses, ten volle te verstaan

A unique mixture of monoterpenes and volatile phenols characterises Zelen wine’s aromatic profile

This study aimed to characterise the aromatic uniqueness of Zelen (Vitis vinifera L.) wines, an autochthonous variety from the Vipava Valley located in Western Slovenia, through chemical and sensory assessment. Seventy aromatic compounds, including varietal thiols, esters, C6- alcohols, volatile phenols, terpenoids, and norisoprenoids, were analysed by HS-SPME-GCMS in two surveys comparing Zelen wines with four other varieties grown in Vipava Valley. The olfactory space of Zelen wines was defined by comparing their aromatic profiles with those of Pinela wines in a sorting task and by the sniffing of aromatic fractions obtained by HPLC fractionation. Zelen wines were characterised by dried herbs and spicy notes such as thyme, rosemary, and basil in comparison to Pinela wines. The chemical profile of Zelen wines was dominated by the presence of an original mixture of monoterpenes, including terpinene isomers, limonene, p-cymene, terpinolene, linalool, and α-terpineol, as well as volatile phenols, 4-vinylguaiacol, and methyl salicylate. The obtained concentrations of 4-vinylguaiacol and methyl salicylate were at levels close to or above the reported olfactory threshold, thus inferring a potential contribution of these compounds to the spicy aromatic components of Zelen wines. Two aromatic fractions reminiscent of herbal notes specific to Zelen wines–isolated by HPLC semi-preparative fractionation and further analysed by HS-SPME-GC-MS–revealed the presence of an original mixture of hydrocarbon monoterpenes, including the compounds that were quantitatively measured, and others, such as β-myrcene, β-phellandrene, E-β-ocimene, Z-β-ocimene, and two 2,4,6-octatriene-2,6-dimethyl isomers. Semi-quantitative measurements showed that this new group of monoterpenes was also present at higher levels in Zelen than in Pinela, Malvasia Istriana, Chardonnay, and Sauvignon blanc wine

MANAGING ALCOHOL IN THE VINEYARD AND THE WINERY: UNDERSTANDING THE IMPACT OF ETHANOL ON WINE FLAVOR AND THE RELATIONSHIP BETWEEN AROMA COMPOSITION AND AROMA PERCEPTION IN SAUVIGNON BLANC AND CABERNET SAUVIGNON WINES

This work consists of two manuscripts, one published, and one ready-to-submit, that embody the same experimental purpose and design with two different well-known wine grapes, Cabernet Sauvignon and Sauvignon blanc. A review of the literature is included beforehand. Ripening and alcohol were investigated for potential impacts to wine aroma and taste. Two different methods of alcohol adjustment, pre-fermentation dilution and post-fermentation membrane filtration, were implemented at three ripening targets for two vintages. Volatile composition was determined quantitatively for the wines and was correlated with significant sensory attributes. Volatile thiols in Sauvignon blanc and methoxypyrazines in Cabernet Sauvignon were quantified in addition to esters, higher alcohols, terpenes, and C13-norisoprenoids. Harvest and alcohol as treatment factors were compared as well as alcohol adjustment method and timing. Sauvignon blanc wine aroma and taste were significantly altered by changes in ethanol concentration but had fewer distinctive aromas at later harvests. Post-fermentation dealcoholization significantly reduced the concentration of volatile esters, as did pre-fermentative dilution of the must using water. Pre-fermentative dilution with sugar solution to increase alcohol concentration led to wines with higher concentrations of volatile esters, terpenes and norisoprenoids that had noticeably higher aroma intensities of tropical fruit, grapefruit, sour candy, and alcohol as well as a hotter mouthfeel and more bitter taste. Volatile thiols 3-mercaptohexanol (3-MH) and 3-merceptohexyl acetate (3-MHA) were affected by harvest timing, not alcohol, though no clear trend was observed for differences between harvests. Unlike Sauvignon blanc wines, evaluating alcohol adjustment effects showed many aroma attributes that remain discriminating for Cabernet Sauvignon wines throughout ripening. Retro-nasal aroma, taste, and mouthfeel were affected more by changes in alcohol than ortho-nasal aroma for Cabernet Sauvignon wines. Higher alcohol wines had more bruised fruit ortho-nasal aroma and more artificial fruit, pepper, and alcohol retro-nasal aroma. Both late harvest wines and high alcohol wines were high in dark fruit aroma but late harvest wines were not described distinctively by the artificial fruit descriptor, likely due to the increased concentrations of volatile esters measured in those wines. Methoxypyrazines 2-isobutyl-3-methoxypyrazine (IBMP) and 2-isopropryl-3-methoxypyrazine (IPMP) behaved incongruently. IBMP was mostly undetectable after the early harvest but was significantly higher, when quantifiable, in all low alcohol treatment wines. IPMP was significantly higher in high alcohol wines and was detected at all harvests at similar concentration ranges. Sensorially, IBMP was highly associated with both pyrazine ortho-nasal and retro-nasal aroma while IPMP associated with bruised fruit and alcohol aromas. It is recommended to harvest early and chaptalize to improve sensory qualities of these wines if more hang time presents a conflict for the vineyard or winery. Adjusting alcohol either before or after fermentation had similar effects on aroma and volatile ester reductions. However, membrane filtration offered more precision in the final outcome