Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 55-60). Also available via the World Wide Web.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: During wine fermentation, numerous grape must constituents serve as nutrients to wine yeast (Saccharomyces cerevisiae), which enable their growth and successful completion of alcoholic fermentation. Many of these nutritional factors, in particular nitrogen, also act as precursors for yeastderived flavour compounds such as higher alcohols, esters and volatile fatty acids. Yeast nitrogen metabolism thus plays a determining role in wine aroma and quality. Not only is the nitrogen source, concentration and supplementation timing important, but various environmental factors and the genetic constitution of the yeast strain used for fermentation will also contribute to fermentation outcomes. The main goal of this work was to explore the complex interactions between a number of contributing factors; namely nitrogen source, timing of addition, yeast strain and fermentation matrix. Broadly, this study assessed the impact of seven different nitrogen combinations, added either to the initial grape must or after the onset of fermentation, on fermentation performance and aroma compound production by nine commercial wine yeast strains. Fermentations were done in synthetic grape must, and validated for a subset of parameters in real grape must. The nitrogen treatments were designed according to the generally established order of preference of S. cerevisiae for individual amino acids as source of nitrogen under fermentative conditions, and the potential of certain amino acids to participate in metabolic pathways that produce specific aroma compounds. The results reveal that different nitrogen combinations can lead to unexpected aroma outcomes, depending strongly on the genetic background of individual yeast strains and the timing of nitrogen addition. Certain nitrogen treatments consistently resulted in significant increases or decreases in specific aroma compound concentrations in comparison to the treatment fermented on ammonium as only nitrogen source, for multiple yeast strains. These compounds were classified as nitrogen treatment dependent. Other aroma compounds were produced similarly for all nitrogen treatments and were designated as nitrogen treatment independent. The presence of specific amino acid groups (for example the branched-chain and aromatic amino acids) could be correlated to significantly altered production patterns of related (such as higher alcohols) or unrelated (diethyl succinate) aroma compounds relative to the other nitrogen treatments. Taken together, a number of interesting and novel hypotheses regarding the metabolic pathways involved could be derived from the data. Ultimately, this initial assessment of interactive effects during fermentation will contribute to practical guidelines for winemakers to allow matching grape must constituents (such as nutrients) with the intrinsic aroma production capabilities of specific yeast strains in order to modulate wine aroma, style and quality. / AFRIKAANSE OPSOMMING: Tydens wynfermentasie dien talle druiwemosbestanddele as voedingstowwe vir wyngis (Saccharomyces cerevisiae) wat hul groei bevorder en hul in staat stel om alkoholiese fermentasie suksesvol te voltooi. Baie van hierdie voedingstowwe, veral stikstof, dien ook as voorlopers vir geurkomponente afkomstig van gismetabolisme, soos hoër alkohole, esters en vlugtige vetsure. Die stikstofmetabolisme van gis speel dus ‘n bepalende rol in wynaroma en -kwaliteit. Nie net is die stikstofbron, konsentrasie en tydsberekening van stikstof toevoeging belangrik nie, maar verskeie omgewingsfaktore, asook die genetiese samestelling van die gisras aangewend vir fermentasie, sal bydra tot die fermentasie uitkomste. Die hoofdoel van hierdie werk was om die komplekse interaksies tussen ‘n aantal bydraende faktore te ondersoek; naamlik die stikstofbron, tyd van stikstof toevoeging, gisras en fermentasiematriks. Breedweg het hierdie studie die impak van sewe verskillende stikstofkombinasies, toegedien tot die druiwemos voor of na die aanvang van fermentasie, op die suksesvolle verloop van fermentasie en die produksie van aromakomponente deur nege kommersiële wyngisrasse bepaal. Fermentasies is in sintetiese druiwemos uitgevoer, en ‘n deelversameling van die fermentasies in regte druiwesap te herhaal. Die stikstofbehandelings is ontwerp in ooreenstemming met die algemeen vasgestelde voorkeurvolgorde van S. cerevisiae vir individuele aminosure as stikstofbron onder fermentatiewe kondisies, en die potensiaal van sekere aminosure om mee te doen in metaboliese paaie wat spesifieke aromaverbindings produseer. Die resultate toon dat verskillende stikstofkombinasies tot onverwagte aroma-uitkomste kan lei wat sterk afhanklik is van die genetiese agtergrond van individuele gisrasse en die tyd van stikstof byvoeging. Sekere stikstofbehandelings het konsekwent, vir veelvuldige gisrasse, tot beduidende toenames of afnames in die konsentrasies van spesifieke aromakomponente gelei in vergelyking met die behandeling wat ammonium as enigste stikstofbron bevat het. Hierdie verbindings is as stikstofbehandeling afhanklik geklassifiseer. Ander aromaverbindings is soortgelyk vir alle stikstofbehandelings geproduseer en is aangewys as stikstofbehandeling onafhanklik. Die teenwoordigheid van spesifieke aminosuurgroepe (byvoorbeeld die vertakte-ketting en aromatiese aminosure) kon gekorreleer word met beduidende veranderings in produksiepatrone van verwante (soos hoër alkohole) of onverwante (dietielsuksinaat) aromakomponente relatief tot die ander stikstofbehandelings. Alles inaggenome kon ‘n aantal interessante en nuwe hipoteses rakende die betrokke metabolise padweë van die data afgelei word. Uiteindelik sal hierdie aanvaklike bepaling van interaktiewe effekte tydens fermentasie bydra tot praktiese riglyne vir wynmakers, wat hulle in staat sal stel om druiwesapbestanddele (soos nutriënte) te strook met die intrinsieke aromaproduksie kapasiteite van spesifieke gisrasse, en sodoende wynaroma, styl en kwaliteit te moduleer. / Oenobrands and THRIP for funding this project

Thesis (MScAgric)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Wine cellars are diverse in terms of equipment types and process configurations. Whilst other food production processes have, in many cases, been properly analysed and modelled, this process diversity has resulted in an absence of process analyses in the wine industry. Each wine cellar is unique and represents a fully integrated agro-business, starting with a raw material (grapes) and extending to marketing and selling of the final product (wine). This makes the wine industry unique in this context. This study is the first attempt to analyse winemaking procedures in the form of a process audit. The study was approached in the following manner: • A questionnaire was developed to assess cellar configurations and conditions. This questionnaire was submitted to a statistically significant number of cellars, and a statistically significant number of questionnaires were returned. • The data collected from the questionnaire were statistically analysed and associations between equipment or procedures and wine faults were identified. • Three cellars were studied in depth. These three cellars had their processes audited and their effluent characterised. Additional data were obtained from current sampling projects and these data were analysed to complement the data obtained from the questionnaire • A preliminary input/output model was developed. The major results of this study are: • It was found that certain faults that appear in wine might be associated with equipment and/or process faults. These associations are statistically significant and they show that cellar hygiene is of critical importance when assessing these wine faults. The most important of these faults are VA, microbial contamination of the wine, sluggish and stuck fermentations. A risk hierarchy was derived to indicate which events are associated with others most strongly. • It was found that few wineries measure water consumption and even fewer wineries measure the quantity of effluent produced. • Correlations have been developed to predict winery parameters in terms of tons of grapes pressed per annum. These parameters include water and electricity consumed, wine produced and the quantity of effluent produced. Effluent characteristics have also been correlated to the tons of grapes pressed per annum. These characteristics include chemical oxygen demand, sodium absorption ratio and total dissolved solids in solution. Chemical oxygen demand was identified as the most important contributing factor in winery effluent. It was shown that all variables rise with an increase in cellar size, but the rise is not linear. This implies that large cellars have greater quantities of effluent of lower quality than small cellars. Most cellars have effluent concentrations that require some form of effluent treatment. The characterisation of effluent shows that the most widely used disposal practice is irrigation, and that the effluent disposed in this manner does not meet legislative requirements. • A preliminary input/output model was developed in order to enable wineries that have not measured the relevant parameters to predict the abovementioned variations. The resolution of these predictions is low but the model serves to provide an initial estimate if there are no data available. The model will give industrial averages for any given cellar size. • An economic balance was performed using this preliminary model. It was shown that if cellars were to lower the consumption of utilities and to reduce the strength of their effluent (using cleaner practices and not dilution) the reduction of operating costs could be reduced by 14% for smaller cellars to 17% for larger cellars. This study has shown that it is possible to make wine in a more environmentally friendly manner, producing better quality wines, without incurring extra costs. / AFRIKAANSE OPSOMMING: Wynkelders is diverse eenhede ten opsigte van die tipe toerusting en prosesse wat gebruik word. Terwyl ander prosesse rondom voedselproduksie in baie gevalle reeds geanaliseer en gemodelleer is, het die diversiteit in die wynindustrie gelei tot 'n afwesigheid van prosesanalises. Elke wynkelder is uniek en verteenwoordig 'n ten voile geintegreerde agro-besigheid wat begin met die rou materiaal (druiwe) en lei tot die bemarking en verkope van die finale produk (wyn), 'n eienskap wat die wynindustrie uniek maak in hierdie verband. Hierdie studie is die eerste poging om die wynmaakproses in die vorm van ‘n proses-oudit te analiseer. Die studie is soos volg aangepak: • ‘n Vraelys is ontwikkel om kelderkonfigurasies en -toestande te ondersoek. Die vraelys is aan ‘n statisties betekenisvolle aantal kelders voorgele, en ‘n statisties betekenisvolle aantal vraelyste is terugontvang. • Die data wat uit die vraelyste ontvang is, is statisties ontleed en verwantskappe tussen toerusting of prosesse en wyngebreke is geidentifiseer. • Drie kelders is in diepte bestudeer. Hierdie drie kelders se prosesse is geoudit en die afvloeiwater is gekarakteriseer. Addisionele data is verkry van huidige projekte en hierdie data is ge-analiseer om die data van die vraelys aan te vul. • ‘n Voorlopige inset / uitset model is ontwikkel. Die belangrikste resultate van hierdie studie is: • Dit is bevind dat sekere gebreke wat in wyn voorkom geassosieer kan word met tekortkominge in toerusting en/of prosesse in die kelder. Hierdie assosiasies is statisties betekenisvol en toon dat kelderhigtene van kritiese belang is wanneer gebreke in wyn ondersoek word. Die mees belangrike gebreke wat voorkom is vlugtige suur, mikrobiese kontaminasie van wyn, slepende en gestaakte fermentasie. ‘n Risikohierargie is afgelei om die gebeure te toon wat die sterktste met mekaar geassosieer word. • Dit is gevind dat min wynkelders waterverbruik meet. Selfs minder kelders meet die hoeveelheid afvloeiwater wat geproduseer word. • Korrelasies is ontwikkel om kelderparameters te voorspel in terme van ton druiwe gepars per jaar. Hierdie parameters sluit in water- en elektrisiteitsverbruik, wyn geprosuseer en hoeveelheid afvloeiwater geproduseer. Eienskappe van afvloeiwater is ook gekorreleer met die ton druiwe wat per jaar gepars word. Hierdie eienskappe sluit in chemiese suurstofbehoeftes, natrium absorpsieverhoudings en totale opgeloste soliede materiaal in oplossing. Chemiese suurstofbehoeftes is geidentifiseer as die mees belangrike bydraende faktor tot afvloeiwater in kelders. Dit is getoon dat alle veranderlikes verhoog hoe groter die kelder, maar hierdie verhoging is nie lineer nie. Dit impliseer dat groter kelder meer afvloeiwater van ‘n laer kwaliteit produseer. Die meeste kelders produseer afvloeiwater van sodanige konsentrasies dat behandeling daarvan nodig is. Die ondersoek van hierdie afvloeiwater toon dat die mees algemene wyse van wegdoening van afvloeiwater besproeiing is, en dat afvloeiwater wat op hierdie manier weggedoen word, nie voldoen aan die wetgewing se vereistes nie. • 'n Voorlopige inset/uitset model is ontwikkel om kelders wat nie die toepaslike parameters gemeet het nie in staat te stel om hierdie parameters te voorspel. Die akuraatheid van hierdie voorspellings is nie hoog nie, maar die model verskaf ‘n aanvanklike skatting waar daar geen data beskikbaar is nie. Die model verskaf industriele gemiddeldes aan kelders van enige grootte. • ‘n Ekonomiese balans is uitgevoer deur van hierdie model gebruik te maak. Dit is getoon dat indien kelders die gebruik van water en elektrisiteit verminder en die konsentrasie van afvloeiwater verlaag (deur van skoner paktyke gebruik te maak, en nie verdunning nie) die bestuurskoste met 14% vir kleiner kelders tot 17% vir groter kelders verlaag kan word. Die studie het getoon dat dit moontlik is om wyn te maak op ‘n meer omgewingsvriendelike wyse, en sodoende beter kwaliteit wyn te produseer sonder addisionele kostes.

Thesis (MScAgric)--Stellenbosch University, 1952. / No Abstract Available

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Nitrogen composition of grape must is highly variable and impacts on the health of the fermenting yeast population as well as the formation of aroma and flavour compounds in wine. Insufficient yeast assimilable nitrogen (YAN), mostly consisting of amino acids and ammonium, can lead to stuck or sluggish fermentations as well as the formation of undesirable compounds such as H2S. Furthermore, it is well established that the total concentration of YAN and the specific amino acid composition have a significant impact on the final aroma and flavour of wines. However, the impact of individual amino acids and of specific amino acid compositions on fermentation kinetics and on the production of aroma and flavour impact compounds under winemaking conditions is not well understood. The first goal of this study was to evaluate the effect of single amino acids on growth kinetics and major volatile production of two industrial wine yeast strains under conditions resembling wine fermentations. To facilitate these fermentation conditions while also allowing for easy reproducibility and manipulation of the initial components, a synthetic grape media was utilized. Biomass formation, exponential growth rate, lag phase, and fermentation duration were utilized to evaluate the efficiency of single amino acids. The data show that previously observed trends in laboratory strains mostly apply to these conditions and strains. In general, the efficiency of amino acids to be used as nitrogen sources and the production of major volatiles due to their presence followed the same patterns for both industrial yeast strains. However, the production of the secondary metabolites butanol, propanol, acetic acid, and ethyl acetate were found to be produced in different final concentrations dependent upon the yeast strain. The branched-chained and aromatic amino acids (BCAAs) treatments were observed to have the most dramatic effects on major volatile production. Investigating the relationships between the initial concentration of the BCAAs and the final concentrations of major volatile compounds, it was found that the production of fusel alcohols and fusel acids due to the degradation of BCAAs by S. cerevisiae could be predicted from the initial concentration of BCAAs. While under simple nitrogen conditions the production of several other secondary metabolites such as butanol, propionic acid, valeric acid, decanoic acid and 2-phenylethyl acetate were found to be correlated to the initial concentration of BCAAs in the media. Future studies should focus on the validation of these trends in aroma production in real grape musts under various fermentation temperatures for a number of industrial wine yeast strains. / AFRIKAANSE OPSOMMING: Die stikstof samestelling van druiwemos is hoogs veranderlik en impakteer op die kerngesondheid van die fermenterende gis populasie asook die produksie van aroma- en geurverbindings in wyn. Onvoldoende assimileerbare stikstof (ook genoem “yeast assimilable nitrogen” (YAN)), wat meestal bestaan uit aminosure en ammonium, kan aanleiding gee tot steek- of slepende fermentasies, asook die vorming van ongewensde verbindings soos H2S. Dit is alombekend dat die totale konsentrasie van YAN en dan ook die spesifieke aminosuur samestelling ‘n noemenswaardige impak op die finale aroma en smaak van wyn het. Die invloed van individuele am inosure en spesifieke aminosuur samestellings op die fermentasie kinetika, asook die produksie van verbindings met ‘n impak op die wyn aroma en smaak, word egter nie deeglik verstaan nie. Die eerste doelwit van die studie was om twee industriële gisrasse te gebruik om die effek van enkel aminosure op die groei-kinetika en produksie van die vername vlugtige verbindings onder wynmaak toestande te bepaal. Kunsmatige, gedefinieerde druiwermosmedium is gebruik om wynmaak toestande te simuleer en ook herhaalbaarheid en manipulering van die aanvanklike samestelling van die medium te verseker. Die studie het vorige tendense wat opgemerk is in die evaluasie van laboratorium rasse onder soortgelyke toestande bevestig. Die doeltreffendheid waarmee aminosure oor die algemeen gebruik word as stikstofbron, asook die produksie van die vernaamste vlugtige verbindings wat gekoppel is aan hulle teenwoordigheid, het ‘n vergelykbare patroon vir beide rasse gevolg. Die sekondêre metaboliete butanol, propanol, asetaat en etiel-asetaat is egter wel in verskillende eindkonsentrasies geproduseer deur die verskillende gisrasse. Die vertakte-ketting en aromatiese aminosuur (“branched-chained and aromatic amino acids” (BCAAs)) behandelings het die mees dramatiese effek op die produksie van die vernaamste vlugtige komponente gehad. Ondersoek na die verwantskap tussen die aanvanklike konsentraies van die BCAAs en die finale konsentrasies van dié verbindings het aangedui dat die produksie van hoër alkohole en sure, as gevolg van die afbraak van BCAAs deur S. cerevisiae, met behulp van die aanvanklike konsentrasie van die BCAAs voorspel kon word. Terselfdertyd is gevind dat onder eenvoudige stikstoftoestande, verskeie ander sekondêre metaboliete soos butanol, propionaat, valeriaat, dekanoësuur en 2-fenieletielasetaat, gekorreleer kan word met die aanvanklike BCAAs in die media. Verdere studies moet poog om hierdie tendense ten opsigte van aromaproduksie te bevestig en wel deur gebruik te maak van ware druiwemos, verskeie fermentasietemperature, asook ’n verskeidenheid van wyngisrasse.

by Tam Siu-man, Ng Ching-hoi, Wong Kam-wah. / With an abstract in Chinese and English / Bibliography: leaves 87-88 / Thesis (M.B.A.)--Chinese University of Hong Kong, 1982

Constituents of the wine matrix, including ethanol, affect adsorption of sulfur volatiles on solid-phase microextraction (SPME) fibers, which can impact sensitivity and accuracy of volatile sulfur analysis in wine. Several common wine sulfur volatiles, including hydrogen sulfide (H2S), methanethiol (MeSH), dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), diethyl disulfide (DEDS), methyl thioacetate (MeSOAc), and ethyl thioacetate (EtSOAc), have been analyzed with multiple internal standards using SPME-GC equipped with pulsed-flame photometric detection (PFPD) at various concentrations of ethanol, volatile-, and non-volatile-matrix components in synthetic wine samples. All compounds exhibit a stark decrease in detectability with the addition of ethanol, especially between 0.0 and 0.5%v/v, but the ratio of standard to internal standard was more stable when alcohol concentration was greater than 1%. Addition of volatile matrix components yields a similar decrease but the standard-to-internal-standard ratio was consistent, suggesting the volatile matrix did not affect the quantification of volatile sulfur compounds in wine. Non-volatile wine matrix appears to have negligible effect on sensitivity. Based on analyte:internal standard ratios, DMS can be accurately measured against ethyl methyl sulfide (EMS), the thioacetates and DMDS with diethyl sulfide (DES), and H₂S, MeSH, DEDS, and DMTS with diisopropyl disulfide (DIDS) in wine with proper dilution. The developed method was then used to quantify sulfur compounds in 21 various California wines. H₂S and MeSH were found in higher concentrations in white varietals, while DMS was slightly higher in red varietals, particularly cabernet sauvignon and merlot. Trace amounts of DEDS and MeSOAc were found in almost all wines. DMS and DMTS were found in all wines, in some instances above reported thresholds. / Graduation date: 2012

Fermentation of the grape must into wine is one of the most important steps in winemaking. Selected yeast strains of Saccharomyces cerevisiae have been used for many years to ensure complete and even fermentations. The formation of volatile compounds also occurs during fermentation and will influence the sensory perception of the wine. The main objective of the research was to study the sensory and chemical composition of 1992 Oregon Riesling, Chardonnay and Pinot Noir wines fermented with different commercial S.cerevisiae strains. In the first study, Free-Choice Profiling was used to study the sensory profiles of all three varieties after 7 and 20 months of aging. This method was used in order to utilize a panel of expert winemakers for the tastings. The sensory data analyzed through Generalized Procrustes Analysis showed that some strains were similar while others were different in terms of aroma and flavor at 7 months of age. After 20 months of aging, differences and similarities were still present although the sensory profiles were different from the young wines. This last finding showed that differences are still present after a period of aging. In the second study, the chemical composition of all three varieties and the volatile composition of selected wines of Riesling and Chardonnay were studied. In both white varieties, statistical differences in titratable acidity, residual sugar, volatile acidity and malate content resulted from fermentation with different yeast strains. The volatile composition was qualitatively similar, but some quantitative differences, as relative concentration, were found. Whether or not those differences had a sensory impact was not investigated. Results of the present study showed the need for further studies in order to understand the role of yeast in flavor development. Relationships between sensory profiles and volatile composition could help winemakers to understand the influence of a selected strain on a particular variety and to select yeast strains to optimize wine quality. / Graduation date: 1995

by Kam Ka Yan, Karen, Tan Wai Hon. / Thesis (M.B.A.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaf 50). / ABSTRACT --- p.ii / TABLE OF CONTENTS --- p.iii / LIST OF ILLUSTRATIONS --- p.iv / LIST OF TABLES --- p.v / Chapter / Chapter I --- INTRODUCTION --- p.1 / Red Wine from the French Bordeaux --- p.1 / Top five Bordeaux wine --- p.2 / Chapter II --- ABOUT WINE AUCTION --- p.4 / Wine auction --- p.4 / Factors affecting the hammer price in wine auction --- p.5 / Chapter III --- METHODOLOGY --- p.7 / Objective and hypothesis --- p.7 / Data collection and translation --- p.12 / Chapter IV --- FINDINGS --- p.15 / Regression analysis of model1 --- p.15 / Chateau Lafite --- p.15 / Chateau Latour --- p.17 / Chateau Haut Brion --- p.19 / Chateau Margaux --- p.21 / Chateau Mouton Rothschild --- p.23 / Combined Data --- p.25 / Regression analysis of Model2 --- p.27 / Chateau Haut Brion --- p.27 / Chateau Latour --- p.29 / Chateau Margaux --- p.31 / Chapter V --- CONCLUSION AND IMPLICATIONS --- p.33 / APPENDIX --- p.35 / BIBILIOGRAPHY --- p.50

Thesis (DScAgric)--Stellenbosch University, 1958. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming