Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Cabernet Sauvignon is the most planted red cultivar in South Africa and the second most planted red cultivar in the Olifants River region. The cultivar is prone to vigorous growth with low yields. Excessive irrigation could accentuate these cultivar characteristics. Considering the foregoing, the aim of the study was to describe how Cabernet Sauvignon will react to climate, soil type (texture) and irrigation within the Lower Olifants River wine region to enable growers to make the right decisions regarding long term as well as short term cultivation practices. This study is part of a project carried out by the ARC Infruitec-Nietvoorbij at Stellenbosch to determine the effects of soil type and atmospheric conditions on yield and wine quality of Cabernet Sauvignon in different grape growing regions of South Africa. Similar studies are being carried out in the Orange River, Stellenbosch and Swartland regions of South Africa. The Lower Olifants River region could be divided into three climatic regions. Furthermore, two climatic regions is evident regarding the formation of grape wine colour and aromas. Proximity to the Atlantic Ocean would play an important role in a cultivar establishment policy. The variation in stem water potential (ΨS) could be related to soil water status expressed in terms of matric potential (ΨM). In the case of sandy soils, ΨS decreased substantially more as the ΨM decreased compared to the sandy loam soils. The reason could be that the unsaturated hydraulic conductivity in sandy soils decreased more rapidly as the ΨM decreased compared to the heavier soils. Thus could explain why the grapevines in the sandy soils experienced more water stress than the ones in the sandy loam soils at a given ΨM. Climate had a strong influence on grapevine water status with grapevines nearer to the ocean experiencing less water stress compared to the ones further inland. This was especially true for grapevines in the sandy soils. Vegetative growth and yield of grapevines in the sandy soils were more sensitive to water deficits compared to the ones in the sandy loam soils. For deficit irrigated grapevines in the sandy soils, vegetative growth and yield decreased by ca. 30% when ca. 55% less water was applied from flowering to harvest. Yield reduction were ca. 15% with no or very little influence on vegetative growth with ca. 80% reduction in water applied from flowering to harvest for grapevines in the sandy loam soils. The influence of soil texture on wine quality and style were evident under intensive irrigation as well as over different climatic regions. Overall sensorial potential wine quality of grapevines in sandy soils tended to be higher compared to the ones in the sandy loam soils. Deficit irrigation tended to increase wine colour intensity, irrespective of soil texture. Furthermore, deficit irrigation in sandy loam soils tended to increase wine fullness and the berry characteristics of the wine. Berry characteristics of wines from the sandy soils tended to be higher compared to the ones from the sandy loam soils. Too severe water deficits in sandy soils could be detrimental to wine quality. Climate tended to have an influence on wine style of grapevines in the sandy soils with wines produced further away from the ocean tended to have higher berry characteristics. Irrigation management could be a powerful tool to manipulate the grapevine in sandy soils. For grapevines the sandy loam soils in addition to regulated deficit irrigation, additional canopy management practices could be needed to improve wine quality. / AFRIKAANSE OPSOMMING: Cabernet Sauvignon is die mees aangeplante rooidruif kultivar in die Suid-Afrikaanse wynbedryf. In die Olifantsriver streek is dit naas Shiraz, die tweede mees aangeplante rooidruif kultivar. Cabernet Sauvignon is bekend as ‘n groeikragtige skaamdraer. Indien oorbesproei word, kan hierdie potensiële nadelige eienskappe nog meer na vore tree. Die doel van die studie is om die invloed van die klimaat, grond en besproeiing op Cabernet Sauvignon se vegetatiewe groei, produksie en wyngehalte in die Benede Olifantsrivier streek te bepaal. Hierdie inligting kan produsente help om ingeligte kortsowel as langtermyn besluite te maak rakende die verbouing van Cabernet Sauvignon. Hierdie studie vorm deel van ‘n breër studie in die Suid-Afrikaanse wynbedryf, gedryf deur die Landbou Navorsingsraad (LNR) Infruitec-Nietvoorbij, Stellenbosch om die invloed van atmosferiese toestande en grond op die produksie en wyngehalte van Cabernet Sauvignon te bepaal. Soortgelyke projekte word uitgevoer in die Oranjerivier, Stellenbosch en Swartland wynstreke. Die Benede Olifantsrivier streek kan verdeel word in drie klimaatstreke op grond van temperatuurdata. In terme van die ontwikkeling van druifkleur en aromas, kan die streek verdeel word in twee klimaatstreke. Die afstand vanaf die Atlantiese Oseaan kan ‘n belangrike rol speel in die ontwikkeling van ‘n kultivarriglynplan vir die streek. Grondwaterstatus, uitgedruk as die matrikspotensiaal (ΨM), kan aanleiding gee tot variasie in middag blaarwaterpotensiaal (ΨS) lesings. Die ΨS van die sand gronde verlaag vinniger soos die ΨM verlaag invergelyke met die sandleem gronde. Dit kan moontlik wees as gevolg van die verskil in die grond onversadigde hidroliese konduktiwiteit. Sand gronde se hidroliese konduktiwiteit verlaag vinniger soos die ΨM verlaag, invergelyke met sandleem gronde. Dit verklaar waarom wingerde in sand gronde by dieselfde ΨM, meer waterspanning ondervind as wingerde in sandleem gronde. Klimaat het ‘n invloed op die waterstatus van die wingerdstok. Wingerde nader aan die see het minder waterspanning ondervind invergelyke met wingerde wat verder in die binneland geleë is. Dit was veral die geval met wingerde in die sand gronde. Vegetatiewe groei en produksie van wingerde in die sand gronde is meer sensitief vir waterspanning as wingerde in die sandleem gronde. Tekortbesproeiing in die sand gronde het die groei asook produksie met ongeveer 30% verlaag deur ongeveer 55% minder water toe te dien vanaf blom tot oes. In teenstelling daarmee is die produksie van wingerde in die sandleem gronde met ongeveer 15% verlaag met geen tot baie min verlaging in die groeikrag. Ongeveer 80% minder water is toegedien vanaf blom tot oes. Grondtekstuur kan wyngehalte en -styl beïnvloed ten spyte van intensiewe besproeiing en klimaatsverskille. Sensoriese potensiële wyngehalte van wingerde in die sand gronde was beter invergelyke met dié van die sandleem gronde. Die wyne vanaf die sand gronde het ook geneig om oor meer bessie intensiteit te beskik as wyne vanaf die sandleem gronde. Tekortbesproeiing neig om die wynkleur intensiteit te verhoog, ongeag van grondtekstuur. Tekortbesproeiing in die sandleem gronde kan ook die volheid van die wyne verbeter, asook die bessie intensiteit van die wyn verhoog. Te hoë waterspanning in die sand gronde kan wyngehalte nadelig beïnvloed. Klimaat kan ook die wynstyl vanaf sand gronde beïnvloed met wyne verder vanaf die see wat oor meer bessie intensiteit beskik as wyne nader aan die see. Beheerde tekortbesproeiing kan as ‘n kragtige hulpmiddel gebruik word om wingerde in die sand gronde te manipuleer. Vir wingerde in die sandleem gronde, addisioneel tot beheerde tekortbesproeiing en normale loofbestuurspraktyke, kan ekstra loofbestuurspraktyke bv. die verwydering van sylootlote, dalk nodig wees om wyngehalte te verbeter.

Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Within-vineyard variability in vigour and water status commonly occurs in South African vineyards. Different soil types found over short distances are probably the main cause of vigour variability, while differences in grapevine water status are commonly induced by lateral water flow in the vineyard, blocked irrigation emitters and differences in soil water-holding capacity. These factors can cause heterogeneous ripening and differences in fruit quality between different parts of the vineyard, an aspect that needs to be avoided as far as possible in order to produce quality wines. Measurements of carbon isotope discrimination (CID) have proved to be a tool to assess grapevine physiology in order to study the effects of environmental parameters on leaf carbon dioxide (CO2) gas exchange and stomatal conductance (gs). Grapevine water deficit stress/strain in reaction to these environmental conditions can then be determined by observing the amount of 13C absorbed by plant material after discrimination of 13C has taken place, and this is influenced by the grapevine stress condition and can indicate water-use efficiency. In this study, the variability of grapevine water status and vigour was determined in order to quantify these parameters in different parts of the vineyard. Two separate trials were conducted, the first at Wellington, South Africa, where different irrigation regimes resulted in variability in grapevine water status between plots. The second trial was at Stellenbosch, South Africa, where plots were divided among different vigour classes and irrigation was applied in different quantities for different irrigation treatments. Within-vineyard variability in water status (Wellington and Stellenbosch) and vigour (Stellenbosch) were then quantified and the effects on some grapevine physiological parameters and berry composition were measured. The treatments in the Wellington trial led to differences in grapevine water status, which could be quantified by measurements of stem water potential (SWP) and leaf water potential (LWP). Soil variability also led to differences in grapevine vigour, which were quantified by measurements of pruning mass, leaf area and shoot length. The effect of the variability in grapevine water status on grapevine physiology was assessed by measuring CID, which was the main focus of the study. Other physiological measurements, such as gs and leaf and canopy temperature, were also conducted. The effect of these conditions on grape berry composition was also studied. In the Stellenbosch trial, soil water content, plant water status measurements (SWP, predawn LWP and LWP), physiological measurements (CID and gs) and berry size measurements were used to classify plots into water status treatments (“wet” and “dry” treatments). The effect of vigour differences was analysed separately from these treatments by using pruning mass as a covariate in the statistical analyses. The effect of vigour variability on the measurements was studied by looking at the effect of the covariate on the measurements, while shoot growth rate, shoot length and leaf area measurements were conducted as vegetative growth measurements. Differences in measurements were then studied between the treatments and between the vigour levels of the different plots. In the Wellington trial, plant water status was determined by irrigation, showing increased stress for treatments that received less irrigation. The differences in plant water status then caused differences in grapevine physiology between the treatments, leading to increased gs for increased irrigation. This of course influenced leaf internal CO2 and therefore CID, although CID was also clearly influenced by berry development. Berry size was influenced by irrigation, with larger berries found in wetter treatments, while berry chemical composition was influenced by the irrigation regime, with increased irrigation leading to increased pH and leading to trends showing increased total soluble solids and malic acid, and reduced total and tartaric acid and colour intensity. In the Stellenbosch trial, plots with higher vigour had increased shoot growth rate, longer shoots and increased leaf area, although topping influenced this. Wet treatment vines also showed slightly longer shoots and larger leaf areas. There were differences in soil water content between the wet and dry treatments, and this led to differences in plant water status. Vigour also influenced pre-dawn LWP, especially in the 2007 season, as higher-vigour vines struggled more to rehydrate through the night. Differences in plant water potential led to differences in grapevine physiology, with increased gs for vines from the wet treatment, while higher-vigour vines had slightly increased gs. The differences in gs led to gas exchange differences and therefore differences in CID, meaning that water status and vigour influenced CID. CID measurements illustrated the long term effect of water status on plant physiology, while measurements such as SWP illustrated the short term effects. CID measurements therefore proved to be accumulative over the season, in contrast to SWP measurements that were much more dependent on the current state of grapevine water status. Other physiological measurements showed that wet-treatment vines had higher photosynthetic rates and evapotranspiration and lower leaf temperatures, while higher-vigour vines had slightly increased evapotranspiration and decreased leaf temperatures. Wet-treatment vines had larger berries, while a higher vigour also led to slightly larger berries. Berry composition was influenced by treatment, where wet-treatment vines had increased pH and total soluble solids, while higher-vigour vines had increased juice pH and, in the 2008 season, decreased total soluble solids. Extremely stressed conditions did not show significant effects on plant water potential, but SWP measurements indicated slightly higher stress for the extremely stressed vines and LWP showed slightly less stressed conditions for these vines. Measurements of gs showed slightly lower values for the extremely stressed vines, while measurements of CID showed large significant differences, with the extremely stressed vines having measurements showing high stress. The measurement therefore indicated highly stressed conditions accurately, while other physiological measurements, such as photosynthetic rate, evapotranspiration and leaf temperatures, only showed trends and no significant differences. Measurements of stomatal conductance reacted to plant water status measurements throughout the diurnal measurement days, while CID only reacted slightly with gs changes during these days and was perhaps influenced more by berry chemical composition and development at this early stage of the season. Vigour and water status therefore influenced grapevine physiology, with a more direct effect by water status and an indirect effect by vigour due to microclimatic differences. This also influenced berry composition and therefore quality. In future studies, CID measurements should be done on juice from which organic acids have been removed in order to eliminate the effect of seasonal berry composition on the measurement. Measurements of CID proved to be an integrative, but sensitive, indicator of grapevine stress, especially at the end of the season. It might at best be useful as a post-harvest management tool for producers or grape buyers, especially for irrigation control, as has also been stated by Van Leeuwen et al. (2007). / AFRIKAANSE OPSOMMING: Binne-wingerd variasie in groeikrag en waterstatus is algemeen in Suid-Afrikaanse wingerde. Verskillende grondsoorte wat na aan mekaar voorkom, is seker een van die vernaamste oorsake van variasie in groeikrag, terwyl verskille in wingerdwaterstatus algemeen deur laterale watervloei in die wingerd, verstopte besproeiingspuite en verskille in grond waterhouvermoë geïnduseer word. Hierdie faktore kan aanleiding gee tot heterogene rypwording en verskille in vrugkwaliteit tussen verskillende dele van die wingerd, ‘n aspek wat so ver moontlik vermy moet word om kwaliteitwyne te kan produseer. Die meting van koolstof-isotoopdiskriminasie (KID) is bewys om as gereedskap te kan dien vir die assessering van wingerdfisiologie om die effekte van omgewingsparameters op blaar koolstofdioksied (CO2) - gasuitruiling en stomatale geleiding (gs) te bestudeer. Die stres/stremming as gevolg van ‘n watertekort in die wingerd in reaksie op hierdie omgewingstoestande kan dan bepaal word deur te kyk na hoeveel 13C deur die plantmateriaal geabsorbeer word ná 13C-diskriminasie plaasgevind het, en dít word deur die wingerdstrestoestande beïnvloed en kan ‘n aanduiding verskaf van die doeltreffendheid van waterverbruik. In hierdie studie is die variasie in wingerdwaterstatus en groeikrag bepaal om hierdie parameters in verskillende dele van die wingerd te kwantifiseer. Twee afsonderlike proewe is uitgevoer, die eerste by Wellington, Suid-Afrika, waar verskillende besproeiingsregimes gelei het tot verskille in die wingerdwaterstatus tussen persele. Die tweede proef was by Stellenbosch, Suid-Afrika, waar persele tussen verskillende groeikragklasse verdeel is en besproeiing in verskillende hoeveelhede vir verskillende besproeiingsbehandelings toegepas is. Binne-wingerd variasie in waterstatus (Wellington en Stellenbosch) en groeikrag (Stellenbosch) is toe gekwantifiseer en die effekte op sekere wingerd-fisiologiese parameters en korrelsamestelling is gemeet. Die behandelings in die Wellington-proef het gelei tot verskille in wingerdwaterstatus, wat deur metings van stamwaterpotensiaal (SWP) en blaarwaterpotensiaal (BWP) gekwantifiseer kon word. Grondverskille het ook gelei tot verskille in wingerdgroeikrag, wat deur metings van snoeimassa, blaaroppervlak en lootlengte gekwantifiseer is. Die effek van die variasie in wingerdwaterstatus op wingerdfisiologie is deur metings van KID bepaal wat die hooffokus van hierdie studie was. Ander fisiologiese metings, soos gs en blaar- en lowertemperatuur, is ook gedoen. Die effekte van hierdie toestande op die samestelling van die druiwekorrels is ook bestudeer. In die Stellenbosch-proef is grondwaterinhoud, metings van plantwaterstatus (SWP, voorsonopgang SWP en BWP), fisiologiese metings (KID en gs) en metings van korrelgrootte gebruik om die persele in waterstatusbehandelings (“nat” en “droë” behandelings) te verdeel. Die effek van verskille in groeikrag is apart van hierdie behandelings geanaliseer deur snoeimassa as ‘n kovariaat in die statistiese analises te gebruik. Die effek van groeikragvariasie op die metings is bestudeer deur ondersoek in te stel na die effek van die kovariaat op die metings, terwyl lootgroeitempo-, lootlengte- en blaaroppervlakmetings as metings van vegetatiewe groei uitgevoer is. Verskille in metings tussen die behandelings en tussen die groeikragvlakke van die verskillende persele is toe bestudeer. In die Wellington-proef is plantwaterstatus deur besproeiing bepaal, met verhoogde stres in behandelings waar daar minder besproeiing toegedien is. Die verskille in plantwaterstatus het dan verskille in wingerdfisiologie tussen die behandelings veroorsaak, wat gelei het tot ‘n verhoogde gs in die geval van verhoogde besproeiing. Dit het natuurlik ‘n effek op die interne CO2 van die blaar en dus op KID gehad, hoewel KID ook duidelik deur korrelontwikkeling beïnvloed is. Korrelgrootte is deur besproeiing beïnvloed, met groter korrels in die natter behandelings, terwyl die chemiese samestelling van die korrel deur besproeiingsregime beïnvloed is. Verhoogde besproeiing het pH verhoog en gelei na tendense wat verhoogde totale oplosbare vaste stowwe en appelsuur, en verminderde totale suur, wynsteensuur en kleurintensiteit getoon het. In die Stellenbosch-proef het persele met hoër groeikrag ook verhoogde lootgroeitempo, langer lote en verhoogde blaaroppervlak getoon, hoewel dit deur top beïnvloed is. Wingerdstokke van die nat behandeling het ook effe langer lote en groter blaaroppervlakke getoon. Daar was verskille in grondwaterinhoud tussen die nat en droë behandelings en dit het verskille in plantwaterstatus veroorsaak. Groeikrag is ook deur voor-sonopgang BWP beïnvloed, veral in die 2007-seisoen, aangesien stokke met hoër groeikrag meer gesukkel het om in die nag te rehidreer. Verskille in plantwaterpotensiaal het gelei tot verskille in wingerdfisiologie, met ‘n verhoogde gs vir stokke in die nat behandeling, terwyl stokke met hoër groeikrag ‘n effens verhoogde gs getoon het. Die verskille in gs het gelei tot verskille in gasuitruiling en dus verskille in KID, wat beteken dat waterstatus en groeikrag ‘n invloed op KID het. KID was meer verteenwoordigend van die langtermyneffekte van water status op plantfisiologie, terwyl metings soos SWP die korttermyneffekte weerspieël het. KID metings was dus akkumalatief oor die seisoen, terwyl SWP metings meer ‘n weerspieëling was van die huidige toestand van plantwaterpotensiaal. Ander fisiologiese metings het getoon dat stokke in die nat behandeling ‘n hoër fotosintesetempo en evapotranspirasie sowel as laer blaartemperature ondervind het, terwyl die stokke met hoër groeikrag effe verhoogde evapotranspirasie en verminderde blaartemperature getoon het. Stokke in die nat behandeling het groter korrels gehad, terwyl hoër groeikrag ook effens groter korrels veroorsaak het. Korrelsamestelling is deur die behandelings beïnvloed, met stokke in die nat behandeling wat verhoogde pH en totale oplosbare vaste stowwe getoon het, terwyl stokke met hoër groeikrag verhoogde pH van die sap en verminderde totale oplosbare vaste stowwe (laasgenoemde in die 2008-seisoen) gehad het. Uitermate toestande van stres het geen beduidende effekte op plantwaterpotensiaal getoon nie, hoewel SWP-metings effens hoër stres vir die uitermate gestresde wingerde getoon het en BWP effens minder gestresde toestande vir hierdie stokke getoon het. Metings van gs het effens laer waardes vir die uitermate gestresde stokke getoon, terwyl metings van KID groot noemenswaardige verskille getoon het, met die metings vir die uitermate gestresde wingerde wat hoër stres aangedui het. Dié meting het dus hoogs gestresde toestande akkuraat aangedui, terwyl ander fisiologiese metings, soos tempo van fotosintese, evapotranspirasie en blaartemperature net tendense en nie beduidende verskille aangedui het nie. Metings van stomatale geleiding het dwarsdeur die dae waarop daaglikse metings gedoen is op plantwaterstatusmetings gereageer, terwyl KID net effens met gs-veranderinge op hierdie dae gereageer het en moontlik meer deur die chemiese samestelling en ontwikkeling van die korrel in hierdie vroeë stadium van die seisoen beïnvloed is. Groeikrag en waterstatus het dus wingerdfisiologie beïnvloed, met ‘n meer direkte effek deur waterstatus en ‘n indirekte effek deur groeikrag as gevolg van mikroklimaatsverskille. Dit het ook korrelsamestelling en dus kwaliteit beïnvloed. In toekomstige studies moet KID-metings gedoen word op sap waarvan die organiese sure verwyder is om die effek van seisoenale korrelsamestelling op die meting uit te sluit. Metings van KID is getoon om ‘n integrerende, maar gevoelige, aanduider van wingerdstres te wees, veral aan die einde van die seisoen. Dit is ten beste miskien bruikbaar as naoesbestuursgereedskap vir produsente of druiwekopers, veral vir besproeiingsbeheer, soos ook reeds deur Van Leeuwen et al. (2007) aangedui is.

Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The quality of wine is influenced and determined by various factors, one of which includes the process of malolactic fermentation (MLF). MLF plays an integral role in the flavour and sensory profile of most red wines as well as some white wines like Chardonnay. This process is conducted by lactic acid bacteria (LAB), specifically of the genera Oenococcus, Lactobacillus, Pediococcus and Leuconostoc. Of these, Oenococcus oeni is best adapted to survive in the harsh wine environment. MLF is defined as the conversion of L-malic acid to L-lactic acid and carbon dioxide. The conversion of the dicarboxylic malic acid to the monocarboxylic lactic acid results in a decrease in acidity and an increase in pH, to give a softer mouthfeel and more favourable flavour profile. A further reason for conducting MLF in wine includes the improvement of microbial stability due to the removal of malic acid as a possible substrate for microorganisms. Recently, research focus has shifted to the ability of MLF and LAB to alter the aroma profile of wine via the production and/or modification of certain aroma compounds. In order for wine LAB to conduct MLF, they need to be able to survive the harsh and challenging wine environment. Conditions in South African wines are particularly challenging due to the long, hot ripening seasons resulting in high sugar concentrations which give high ethanol concentrations. Some LAB also struggle to adapt to an environment with high pH and low malic acid concentrations. These factors, combined with the use of sulphur dioxide, cause LAB to struggle in conducting and completing successful MLF. Many of the commercial starter cultures that are currently available contain LAB that have not been isolated from South African wine and are therefore not optimal for use under these challenging wine conditions. Oenococcus oeni is also the single LAB culture present in all commercially available starter cultures. The overriding goal of this study was to create a MLF starter culture containing a mixture of LAB cultures, namely O. oeni and Lactobacillus plantarum, which can successfully convert malic acid to lactic acid, ensure microbial stability, but also make a positive contribution to the wine aroma profile. Lactobacillus plantarum has previously been considered for possible use in a commercial starter culture. The LAB isolates used in this study were selected from the Institute for Wine Biotechnology culture collection as well as isolated from spontaneous MLF. The first objective was to characterise these LAB strains for important traits and for possible use as a MLF starter culture. A total of 23 strains were identified as O. oeni and 19 strains as Lb. plantarum. The identified strains were screened in a synthetic wine medium for their ability to convert malic acid to lactic acid. Based on the LAB strain performance in the synthetic wine medium, seven strains of both O. oeni and Lb. plantarum were selected. These 14 strains were screened for the presence of genes encoding for enzymes responsible for biogenic amine production and were found to contain none of the genes associated with the formation of histamine, tyramine or putrescine. The LAB strains were genetically screened for enzymes associated with aroma modification by LAB during MLF. The enzymes of interest that were screened for included β-glucosidase, esterase, protease and phenolic acid decarboxylase (PAD). The Lb. plantarum strains were found to possess more diverse enzymatic profiles related to aroma than O. oeni. The biggest differences were observed for the presence of β-glucosidase and PAD. The second objective was to perform small-scale fermentations with the individual LAB isolates. The individual isolates were evaluated in Pinotage and based on these results; three strains of each O. oeni and Lb. plantarum were selected for evaluation in mixed culture fermentations. The mixed cultures were evaluated in Pinotage, Shiraz and Cabernet Sauvignon in the 2008 vintage. As a third objective, the wines were also analytically and sensorially evaluated to investigate the changes in the aroma profile that could be attributed to the presence of the mixed LAB isolates. Based on the fermentation data as well as data pertaining to the aroma modification, three mixed cultures were selected for evaluation in the 2009 vintage in Pinotage, Cabernet Sauvignon and Chardonnay. The mixed cultures were able to successfully complete MLF in fermentation periods comparable to that of a commercial culture used as control. The different LAB cultures had distinct and diverse effects on the wine aroma profile. The O. oeni strain played a larger role in the ester concentration present after MLF, while the Lb. plantarum strain had a larger effect on the higher alcohol and volatile fatty acid concentration upon completion of MLF. The results generated by this novel study clearly indicate the potential of a mixed LAB starter culture for conducting MLF. The mixed cultures successfully completed MLF and made a positive contribution to the wine aroma profile. / AFRIKAANSE OPSOMMING: Die kwaliteit van wyn word beïnvloed en bepaal deur verskeie faktore en wynbereidings prosesse, wat die proses van appelmelksuurgisting (AMG) insluit. AMG speel ’n integrale rol in die sensoriese profiel van meeste rooiwyne, sowel as sommige witwyne soos Chardonnay. AMG word gedefinieër as die omskakeling van L-appelsuur na L-melksuur en koolstofdioksied. Hierdie omskakeling kan toegeskryf word aan die teenwoordigheid van melksuurbakterieë (MSB), spesifiek spesies van die genera Oenococcus, Lactobacillus, Pediococcus en Leuconostoc. Vanuit hierdie wyn MSB, is Oenococcus oeni die spesies wat die beste aanpas en oorleef onder stresvolle wyn kondisies. Die omskakeling van appelsuur, ’n dikarboksielsuur, na melksuur, ’n monokarboksielsuur, lei tot ‘n vermindering in suurheid en ’n verhoging in pH. Hierdie vermindering in suurheid gee ’n sagter en meer geronde mondgevoel aan die wyn en dra by tot ‘n meer aangename geurprofiel. ’n Verdere rede vir AMG in wyn is om mikrobiese stabiliteit te verseker deurdat appelsuur verwyder word as ’n moontlike koolstof substraat vir mikroörganismes. Onlangs het navorsing begin fokus op AMG en die vermoë van MSB om die aroma profiel van wyn te beïnvloed deur die produksie/modifisering van sekere aroma komponente. Vir MSB om AMG te kan deurvoer, moet hulle kan oorleef in die stresvolle wynomgewing. Wyntoestande in Suid-Afrika is veral uitdagend vir die oorlewing van mikroörganismes as gevolg van lang, warm somers wat lei tot ’n matriks met ’n hoë suikerkonsentrasie en wyn met ’n hoë etanolkonsentrasie. ‘n Omgewing met ‘n hoë pH en lae appelsuur konsentrasie, kan ook bydrae tot stresvolle kondisies vir MSB. Hierdie parameters, tesame met die gebruik van swaweldioksied, maak dit moeilik vir MSB om AMG te inisieer en te voltooi. Sommige van die kommersiële aanvangskulture wat tans beskikbaar is, bevat nie MSB wat onder Suid-Afrikaanse wyntoestande geïsoleer is nie en daarom is dit nie altyd optimaal vir gebruik nie. Oenococcus oeni is ook die enkele MSB kultuur wat in alle kommersiële kulture gebruik word. Die hoofdoelwit van hierdie studie was om ’n potensiële kommersiële aanvangskultuur te ontwikkel wat ‘n mengsel van MSB bevat. Hierdie aanvangskultuur moet AMG suksesvol kan voltooi, mikrobiologiese stabiliteit bevorder en steeds die wynaroma positief kan beïnvloed. Bakterierasse van O. oeni en Lb. plantarum is geselekteer vir gebruik in hierdie studie. Lactobacillus plantarum het reeds in vorige studies potensiaal getoon as ‘n moontlike aanvangskultuur. Die MSB isolate vir hierdie studie is geselekteer uit die Instituut vir Wynbiotegnologie se kultuurversameling en geïsoleer uit spontane AMG fermentasies. Die eerste doelwit was om hierdie MSB isolate te karakteriseer vir belangrike eienskappe en die moontlike gebruik as ’n kommersiële AMG aanvangskultuur. ‘n Totaal van 23 O. oeni en 19 Lb. plantarum isolate is geïdentifiseer. Hierdie isolate is in ’n sintetiese wynmedium geëvalueer vir hul vermoë om appelsuur na melksuur om te skakel. Op grond van hul reaksie in die sintetiese wynmedium, is sewe isolate van elk van die O. oeni en Lb. plantarum geselekteer. Hierdie 14 isolate is ondersoek vir die teenwoordigheid van die gene wat kodeer vir biogeenamien produksie en daar is gevind dat geen van die isolate enige van die biogeenamien gene wat ondersoek is, naamlik histamien, tiramien en putresien besit nie. Die MSB isolate is geneties ondersoek vir die teenwoordigheid van dié gene wat kodeer vir ensieme wat die aromaprofiel tydens AMG beïnvloed. Dié ensieme sluit β-glukosidase, esterase, protease, fenoliese suurdekarboksilase en sitraatliase in. Daar is gevind dat die Lb. plantarum isolate meer diverse ensiemprofiele as O. oeni besit. Die grootste verskille in die ensiemprofiele kan toegeskryf word aan die teenwoordigheid van β-glukosidase en fenoliese suurdekarboksilase. Die tweede doelwit was om kleinskaalse AMG fermentasies met die individuele MSB isolate uit te voer. Die individuele isolate is in Pinotage geëvalueer. Volgens hierdie resultate is drie isolate van elk van die O. oeni en Lb. plantarum geselekteer om in gemengde kulture getoets te word. Die gemengde kulture is in Pinotage, Shiraz en Cabernet Sauvignon in 2008 geëvalueer. As ’n derde doelwit is hierdie wyne ook analities en sensories geëvalueer om die veranderinge in die aromaprofiele as gevolg van die teenwoordigheid van die MSB te ondersoek. Op grond van die fermentasiedata, sowel as die data oor die aromaveranderinge, is drie gemengde kulture geselekteer vir evaluering in Pinotage, Cabernet Sauvignon en Chardonnay in 2009. Die gemengde kulture kon AMG suksesvol voltooi met fermentasietempo’s wat vergelykbaar was met dié van ‘n kommersiële AMG kultuur wat as kontrole gebruik is. Die verskillende MSB kulture het spesifieke en uiteenlopende uitwerkings op die wynaroma gehad. Die O. oeni isolaat in die gemengde kultuur blyk ‘n belangriker rol te speel in die esterkonsentrasie na AMG, terwyl die Lb. plantarum isolaat ’n groter effek het op die hoër alkohol en vlugtige vetsuurinhoud na AMG. Die resultate wat deur hierdie unieke studie gegenereer is, gee ’n aanduiding van die potensiaal van ’n gemengde MSB aanvangskultuur vir AMG. Die gemengde kulture kon AMG suksesvol voltooi en ‘n positiewe bydrae tot die aromaprofiel van die wyn lewer.

Thesis (MScAgric) -- University of Stellenbosch, 2001. / ENGLISH ABSTRACT: There is an increasing demand by the consumer for knowledge and understanding of the origin of each wine produced. This origin is directly linked to the interaction between the environment and grapevine, and therefore to the terroir. A terroir can be defined as a complex of natural factors being expressed through the final product and must therefore be studied in two steps, namely, the identification of relatively homogenous natural terroir units followed by their ecophysiological characterisation. The aim of this study was to characterise the Bottelaryberg-Simonsberg-Helderberg wine growing area according to existing digital information and to identify natural terroir units. The study area is situated to the southwest of Stellenbosch and covers an area of approximately 25 000 ha. Topography is a static feature of the landscape and affects the sunlight interception by a slope, exposure of a site to winds and drainage of soil water and air. It forms an important component of the terroir concept and has a strong interaction with the environmental components of climate and soil. The study area is bordered by mountains and bisected by a river valley resulting in a large variation in aspect and altitude affecting both spatial and temporal temperature variability. There is no doubt as to the important effect of climate on wine character and quality. A number of indices can be used to describe the regional climate. The study area has a Mediterranean climate with notable spatial variation of all climatic parameters due to its complex topography and proximity to the ocean. The effect of geology on wme character is less clear but appears to act through its contribution to the physical properties of the soil. In the Bottelaryberg-Simonsberg- Helderberg study area the geology is complex due to the high degree of tectonic movement and mixing of parent material. In situ weathering of rocks is seldom the only source of soil formation. Soil has a number of contributing factors affecting wine character and quality, inter alia, soil colour, temperature, chemical composition, depth and texture (affecting the water supplying properties of the soil). It is the last two that appear to have the most significant effect. Soil depth affects the buffer capacity of the soil to temper climatic extremes and the water supply has a well-recorded effect on vine growth and functioning. There is a high degree of soil variation in the Bottelaryberg-Simonsberg-Helderberg study area that is difficult to represent in soil associations. A pattern of soil distribution, however, can be noticed in relation to landscape variation. Terrain morphological units, altitude and aspect were used as pnmary keys for the identification of natural terroir units. Broad soil categories and geological information were included at a secondary level. This resulted in 195 units. These natural terroir units will form the basis for future ecophysiological characterisation in order to determine possible future cultivar distribution as well as the terroir effect on wine character. / AFRIKAANSE OPSOMMING: Daar is toenemende aanvraag vanaf die verbruiker vir kennis en begrip van die oorsprong van elke wyn wat geproduseer word. Die oorsprong is direk aan die interaksie tussen die omgewing en wingerd gekoppel, en daarom ook die terroir. Terroir kan omskryf word as die kompleks van natuurlike faktore wat in die finale produk uitdrukking vind en studies daarvan moet dus in twee stappe plaasvind, d.i. die identifisering van relatiewe homogene natuurlike terroir eenhede gevolg deur die ekofisiologiese karakterisering daarvan. Die doel van die studie was om die Bottelaryberg-Simonsberg-Helderberg wynproduserende gebied te karakteriseer, met behulp van bestaande versyferde data en om natuurlike terroir eenhede te identifiseer. Topografie is 'n vaste landskapskenmerk en beïnvloed sonligonderskepping deur hellings, blootstelling van 'n ligging aan wind en die dreinerin~ van grondwater en beweging van koue lug. Dit is 'n belangrike deel van die terroir konsep en het sterk interaksie met omgewingsfaktore van grond en klimaat. Die studiegebied word begrens deur berge en is deursny deur 'n riviervallei, met groot variasie in helling en aspek. Beide hiervan beïnvloed die ruimtelike- en daaglik-variasies in daaglikse maksimum temperatuur. Die belangrike effek van klimaat op wynkarakter en kwaliteit is duidelik soos weerspieël deur die beskikbaarheid van 'n aantal makroklimaatsindekse. Alle klimaatsparameters word deur topografie beïnvloed. Temperatuur en relatiewe humiditeit word ook deur afstand vanaf die see beïnvloed. Die studie area het 'n Meditereense klimaat, met merkwaardige ruimtelike variasie van alle klimaatsparameters. Die effek van geologie op wynkarakter is minder duidelik, maar het waarskynlik 'n effek op die fisiese eienskappe van 'n grond. Die geologie in die Bottelaryberg-Simonsberg- Helderberg studiegebied is kompleks, as gevolg van die hoë graad van tektoniese beweging en vermenging van moedermateriaal. In situ vorming van gronde uit gesteentes vind selde plaas: Grond het 'n groot aantal bydraende faktore, wat wynkarakter en -kwaliteit kon beïnvloed, onder andere, grondkleur, -temperatuur, -chemiese samestelling, -diepte en -tekstuur (wat die waterleweringsvermoë van die grond bepaal). Dit is veral laasgenoemde twee faktore wat blykbaar die mees opvallendste effek openbaar. Gronddiepte bepaal die buffer kapasiteit van die grond om klimaatsuiterstes te kan weerstaan en die waterleweringsvermoë het 'n alombekende effek op wingerdgroei en funksionering. Daar is 'n hoë graad van grondvariasie in die Bottelaryberg-Simonsberg-Helderberg studiegebied wat moeilik is om met grondassosiasies weer te gee. Daar is wel 'n patroon van grond distribusie wat verband hou met landskapvariasie. Terrein morfologiese eenhede, hoogte en aspek is gebruik as primêre sleutels vir die indentifisering van natuurlike terroir eenhede. Globale grondkategorieë en geologiese inligting is op 'n sekondêre vlak gebruik. Dit het 195 eenhede tot gevolg. Die natuurlike terroir eenhede sal die basis vorm vir toekomstige ekofisiologiese karakterisering, om die terroir effek op wynkarakter te kan bepaal.

Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosach, 2010. / ENGLISH ABSTRACT: Cabernet Sauvignon, the most planted red wine cultivar in South Africa, is prone to vigorous growth with low yields. The aim of the study was to describe how Cabernet Sauvignon grapevines react to climate and irrigation within the Swartland region. Such knowledge would assist growers in decisions regarding long term as well as short term cultivation practices. This study was part of a larger project carried out by the Infruitec-Nietvoorbij institute of the Agricultural Research Council at Stellenbosch to determine effects of soil type and climate on yield and wine quality of Cabernet Sauvignon. The larger project was carried out in selected grape growing regions, i.e. Stellenbosch, Swartland, Lower Olifants River and Lower Orange River. Due to the proximity to the Atlantic Ocean, the study area in the Swartland region could be divided into two climatic regions for viticulture. Grapevines near Philadelphia closer to the ocean experienced less water constraints compared to those further inland near Wellington. Variation in stem water potential could also be related to soil water matric potential. Climate tended to have a more pronounced effect on the grapevine response to water constraints further inland than closer to the ocean. Vegetative growth, berry size and yield depended on water constraints experienced by the grapevines. In the warmer climate, severe constraints reduced yield. In the warmer climate, grapes started to ripen earlier than those in the cooler climate. Sugar concentration (mg/mL) was highest where grapevines experienced moderate water constraints. These seemingly balanced grapevines had the highest sugar accumulation, probably due to optimum photosynthesis and carbohydrate utilization. Low water constraints increased vegetative growth which could have been a sink for sugar loading. In addition to sugar loading, degree Balling (°B) increases could also have been due to a concentration effect where water constraints reduced berry volume. Therefore, °B is probably not a representative indicator of grapevine functioning. Anthocyanin biosynthesis, as quantified on a per berry basis, showed that sugar and anthocyanin could be co-regulated, with anthocyanin biosynthesis reaching a plateau when the sugar content per berry reached 200 mg/mL to 220 mg/mL. At véraison, the most intense grape colour occurred where grapevines experienced moderate water constraints, i.e. single drip line at Wellington and no irrigation at Philadelphia. However, at harvest grapes from the cooler climate tended to have more intense colour and higher phenolics, indicating that lower temperatures favoured anthocyanin biosynthesis. These results supported earlier findings that grapevine water status influences berry volume and dynamics of berry ripening. Water constraints tended to increase sensorial wine colour intensity, as well as wine fullness. Moderate water constraints at both localities resulted in the best sensorial wine quality. Yet there were indications that too severe water constraints could be detrimental to wine quality. Irrigation can be used to manipulate grapevine growth in warmer climates, but might be less effective in cooler climates. In warmer climates, moderate water constraints required to achieve balanced grapevine functioning can be obtained with single drip irrigation, but this might not be the case in cooler climates. / AFRIKAANSE OPSOMMING: Cabernet Sauvignon, die mees aangeplante rooiwynkultivar in Suid-Afrika, is geneig tot kragtige groei met lae opbrengste. Die doelwit van hierdie studie was om te beskryf hoe Cabernet Sauvignon-wingerdstokke reageer op klimaat en besproeiing in die Swartland-streek. Hierdie kennis sal kwekers help wanneer hulle besluite moet neem oor langtermyn sowel as korttermyn verbouingspraktyke. Hierdie studie was deel van ‘n groter projek deur die Infruitec-Nietvoorbij Instituut van die Landbounavorsingsraad op Stellenbosch om die effekte van grondtipe en klimaat op die opbrengs en wynkwaliteit van Cabernet Sauvignon te bepaal. Die groter projek is in geselekteerde wingerdverbouingstreke uitgevoer, nl. Stellenbosch, Swartland, Benede Olifantsrivier en Benede Oranjerivier. As gevolg van die nabyheid daarvan aan die Atlantiese Oseaan kon die studiegebied in die Swartland-streek in twee klimaatstreke vir wingerdbou verdeel word. Wingerdstokke by Philadelphia, wat nader aan die oseaan is, het minder waterstremming ervaar as dié verder binnelands naby Wellington. Veranderinge in stamwaterpotensiaal hou moontlik ook verband met die grondwater- matrikspotensiaal. Klimaat het ‘n groter effek op die reaksie van die wingerdstok op waterstremming verder binnelands as nader aan die oseaan. Vegetatiewe groei, korrelgrootte en opbrengs was afhanklik van die waterstremminge wat deur die wingerdstokke ervaar is. In die warmer klimaat het die ernstige stremminge opbrengs verminder. In die warmer klimaat begin druiwe vroeër ryp word as in die koeler klimaat. Suikerkonsentrasie (mg/ml) was die hoogste waar wingerde matige waterstremming ervaar het. Hierdie skynbaar gebalanseerde wingerdstokke het die hoogste suikerakkumulasie vertoon, moontlik as gevolg van optimum fotosintese en koolhidraatverbruik. Lae waterstremming het vegetatiewe groei verhoog, wat ook ‘n vraagpunt vir suikerlading kon wees. Benewens suikerlading kon verhogings in grade Balling (°B) ook moontlik aan ‘n konsentrasie-effek toegeskryf word in terme waarvan waterstremming die korrelvolume verminder het. °B is dus moontlik nie ‘n verteenwoordigende indikator van wingerdstokfunksionering nie. Antosianienbiosintese, soos gekwantifiseer op ‘n per-korrel basis, het getoon dat suiker en antosianien saam gereguleer kon word, en dat antosianienbiosintese ‘n plato bereik het wanneer die suikerinhoud per korrel 200 mg/mL tot 220 mg/mL was. By deurslaan het die mees intense druifkleur voorgekom waar die wingerdstokke matige waterstremming ervaar het, d.w.s. enkel druplyn op Wellington en geen besproeiing op Philadelphia. Teen oes was die druiwe in die koeler klimate egter geneig om meer intense kleur en meer fenole te bevat, wat aandui dat laer temperature antosianienbiosintese bevoordeel. Hierdie resultate ondersteun vroeër bevindings dat die waterstatus van die wingerdstok ‘n invloed op korrelvolume en die dinamika van korrelrypwording het. Waterstremming neig om die sensoriese wynkleurintensiteit te verhoog, asook die volheid van die wyn. Matige waterstremming op beide liggings het aanleiding gegee tot die beste sensoriese wynkwaliteit. Tog was daar aanduidings dat waterstremming wat te straf was, nadelig kon wees vir wynkwaliteit. Besproeiing kan gebruik word om wingerdgroei in warmer klimate te manipuleer, maar is moontlik minder effektief in koeler klimate. In warmer klimate kan die matige waterstremming wat benodig is vir gebalanseerde wingerdstokfunksionering, verkry word deur enkel drupbesproeiing, maar dit is moontlik nie die geval in koeler klimate nie.

Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2011. / Includes bibliography. / ABSTRACT: The grapevine must constantly find a balance between two continually changing environments, the rhizosphere (i.e. soil) and the troposphere (i.e. macroclimate). The adaptations are extremely complex because they encompass complicated and interrelated processes that are not yet fully understood. In terms of water-use behaviour, differences between cultivars have been described in the literature. In this study, the water status and stomatal conductance of four cultivars (Shiraz, Grenache, Pinot noir and Chardonnay) grafted onto R99 were studied. Diurnal cycles of water status and stomatal conductance, from 07:00 to 19:00, were followed for a single day at the end of the 2009 season. The results showed that, at the end of the season, Shiraz was subjected to water stress conditions, losing leaves and showing symptoms of berry shrivelling. The other three cultivars had a much better canopy status and no symptoms of berry shrivelling were observed. Based on the canopy observations and a comparison of the curves of stem water potential (Ψs) and stomatal conductance (gs), it seems that Pinot noir and Chardonnay are closer to the water-use behaviour of Grenache noir, which is known as a “pessimistic” cultivar, than to Shiraz, which is an “optimistic” cultivar. A study of four plots each of Chardonnay/101.14 Mgt and Shiraz/101.14 Mgt was carried out in eight commercial vineyards in the Robertson region in order to investigate the relationship between soil and root morphology, and the influence thereof on canopy development and berry growth. These plots had different soil types. Important soil properties are reported to limit root growth, individually or as a combination of restrictions. It was found that the size of the root system of 101.14 Mgt is defined by soil physical and chemical properties. The roots of 101.14 Mgt under irrigation can grow to a depth of 100 cm or beyond if the soil physical and chemical properties allow it. Because the soil properties define the root system and the water storage/drainage, they greatly influence the plant water status, even under irrigation. In an arid zone like Robertson, irrigation is an important management tool. The balance between canopy growth before véraison and the ability of the root-soil system to maintain that canopy size during the ripening process is crucial in an area with a high evaporative demand. In this regard, not all the soil properties-root system combinations showed satisfactory performance in maintaining the canopy functioning, which affected berry sugar loading and berry volume. In another study that is presented, forty soil profiles were characterised in the Robertson valley. The root systems were considered as a product of the soil properties, and thus the morphology of the root systems was used as a starting point to group soils together. The importance of soil depth has been described well, thus the root systems were first classified according to rooting depth – into shallow and deep root systems. The deep root systems were then subdivided, creating two subgroups of high root density and low root density. The two extreme groups (i.e. shallow roots, and deep roots with high root density) have particularly different soil properties. The soil characteristics found in these extremes are represented up to certain point by families of the South African soil taxonomy, mainly due to the restrictive function of the B horizon. This restrictive function is related to soil properties that are taken into consideration in the South African soil classification and that are important for grapevine root growth, as well as the thickness of the described horizons and the physical and chemical differences between the horizons. Soil properties have an important influence on root morphology. Due to the fundamental role played by the root system in the overall plant functioning, soil properties are of critical importance. In an arid area, the low water pressure in the atmosphere and the high temperature greatly affect the plant water status. The soil-root system combination plays an important role in the ability of the root system to supply the plant with water during times of high evaporative demand. Different cultivars will react differently due to differences in transpiration control. The maintenance of an adequate water status will have an immense influence on canopy development and maintenance, and on normal and steady berry ripening. In this study it was found that not all the soil-root combinations can fulfil this satisfactorily. Thus, the grapevine balance determined by the combination of the soil-root-canopy complex and the influence of management techniques is extremely important for the favouring of a good canopy:root system ratio, a functional canopy throughout the season and a steady berry ripening curve.

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.

Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2011. / Includes bibliography. / ENGLISH ABSTRACT: Grape and wine phenols consist of flavanols which is the building blocks for tannins. These building blocks are called monomers which consist of catechins, epicatechins, epigallocatechins and epicatechin-gallate. Tannin is important in wine as it contributes to bitterness, mouth feel (astringency) and maturation potential of the wine. Futhermore it has a health benefit as an antioxidant. Anthocyanins are responsible for the colour of red wine. The anthocyanins combine with tannins to form stable polymeric pigments. Due to the importance of tannins and anthocyanins in wine, it is imperitative that different winemaking techniques are used to extract as much of these components as possible and that the analysis is done quickly and accurately. The aim of this study was to evaluate different winemaking techniques and their extraction of tannins and anthocyanins into the wine. Too much tannin extraction can have a negative effect on the sensory quality of the wine. Therefore a second aim was to evaluate the mouth feel properties of a Shiraz wine. A third aim was to compare the two tannin precipitation methods in terms of time efficiency, repeatability and the ease of practice. To investigate the amount of tannin concentration extracted by different winemaking techniques, two cultivars (Cabernet Sauvignon and Shiraz) were used. These treatments included the addition of an enzyme during fermentation [E], cold maceration [CM], post maceration [PM] and the combination of cold and post maceration [CM+PM]. The grapes were harvested in two different climatic areas during the 2008 and 2009 vintages. The two climatic areas were classified according to the Winkler scale as a III (Morgenster) and a IV (Plaisir de Merle). The grapes were harvested at two different ripeness levels in order to evaluate the effect of the different winemaking processes on the extraction of tannins and anthocyanins. One harvest was before (LB) and the other after (HB) the commercial harvest. The results of this study showed significant differences in the phenolic composition of the wines. It was found that the warmer area showed higher tannin concentrations than the cooler area for both cultivars. In the 2008 Cabernet Sauvignon the CM extracted higher concentrations of tannin from the cooler area at both ripeness levels. In the warmer area, CM extracted the highest tannin concentration HB, but the CM+PM extracted the highest tannin concentration from Cabernet Sauvignon at the LB and CM at the HB of the warmer area. In 2009 the PM extracted the highest concentration of tannin at the lower ripeness level, while the E treatment extracted the highest concentration from the warmer area. In the cooler area the CM+PM extracted the highest concentration of tannin at a lower ripeness level, while there were no siginicant differences between the different treatments at the higher ripeness level. The highest anthocyanin concentration was found in the cooler area. The CM treatment was found to have no effect on anthocyanin extraction. Different methods are available to quantify the tannin concentration in wine. Two of the most popular tannin analytical methods are the bovine serum albumin (BSA) and the methyl cellulose precipitable tannin (MCP) methods. The BSA method is a very complex method which uses at least 3 times more reagents than the MCP method. The MCP method only analyzes tannins, while the BSA method analyzes tannins, monomeric pigments (MP), small polymeric pigments (SPP) and large polymeric pigments (LPP). In this study a good correlation was found between the two tannin precipitation methods (R2 – 0.88). There is controversy regarding the variability of these methods. Some scientists found that the two methods show a good correlation with HPLC, while others found that there was no such correlation between the precipitation methods and the HPLC. The MCP method had a practical advantage as it could be performed in half the time required for the BSA method. This has a significant impact in scenarios where a high sample throughput is required although it only measures total tannin. The phenolic composition and mouth feel of the wine was strongly influenced by the climatic area. In the warmer area the effect of tannin concentration on mouth feel was much less than in the cooler area. The wine made of riper grapes, was more grippy, bitter and numbing than the wines made from greener grapes. The E treatment was especially associated with a dry, grippy sensation. / AFRIKAANSE OPSOMMING: Druif en wyn fenole bestaan uit flavanole wat weer die boublokke is van tanniene. Hierdie boublokke, wat bekend staan as monomere, betsaan uit katesjiene, epikatesjiene, epigallokatesjiene an epikatesjien-gallaat. Tanniene is belangrik in wyn aangesien dit bydra tot bitterheid, mondgevoel (vrankheid) asook die verouderingspotensiaal van wyn. As antioksidante hou dit ook gesondheidsvoordele in. Antosianiene dra by tot die kleur van rooiwyn. Antosianiene kombineer met tanniene om meer stabiele polimeriese pigmente te vorm. As gevolg van die belangrikheid van tanniene en antosianiene is dit van uiterse belang dat verskillende wynmaak tegnieke gebruik word om ekstraksie in die wyn te bevoordeel en dat die analitiese metode so vinnig en akkuraat as moontlik gedoen word. Die eerste doel van hierdie studie was om die ekstraksie van tanniene en antosianiene deur middel van verskillende wynmaak tegnieke te evalueer. Te veel tanniene in die wyn kan negatiewe sensoriese kwaliteit tot gevolg het. Daarom is die tweede doel om die sensoriese kwaliteit van Shiraz wyn te evalueer. Die derde doel van hierdie studie was die twee tannien presipitasie metodes met mekaar te vergelyk in terme van die moeilikheidsgraad van die metode, tyd doeltreffendheid en herhaalbaarheid. Verskillende wynmaak tegnieke (ensiem byvoegings [E], koue maserasie [CM], verlengde dopkontak [PM] en ‘n kombinasie van koue maserasie en verlengde dopkontak [CM+PM]) is vergelyk ten opsigte van tannien en antiosianien ekstraksie. In 2008 en 2009 is twee kultivars (Cabernet Sauvignon en Shiraz) in twee verskillende klimatologiese areas gepars. Hierdie areas is geklassifiseer in die Winklerskaal as ‘n IV (Plaisir de Merle) en ‘n III (Morgenster). Om die effek van die verskillende wynmaak tegnieke op die ekstraksie van antosianiene en tanniene te vergelyk, is hierdie twee kultivars by twee verskillende rypheidsgrade geoes. Die eerste oes was net voor kommersiële oes (LB) en die tweede oes het net na kommersiële oes (HB) plaasgevind. Die 2009 Shiraz wyn is organolepties beoordeel om die effek van die verskillende wynmaak tegnieke op die wyn se mondgevoel te vergelyk. Die resultate van hierdie studie toon beduidende verskille in die fenoliese samestelling van die wyne. Dit is gevind dat die warmer area hoër tannien konsentrasies het as die koeler area. In 2008 het die CM+PM die meeste tanniene uit die Cabernet Sauvignon geëkstraheer by LB en die CM by HB in die warmer area. Die CM het in die koeler area meer tanniene geëkstraheer by beide die LB en HB rypheidsgrade. In 2009 het PM die meeste tanniene geëkstraheer by LB terwyl E die meeste tanniene geëkstraheer in die warmer area. In die koeler area het CM+PM die meeste tanniene geëkstraheer, terwyl geen van die behandelings ‘n effek gehad het by HB. Die meeste antosianien konsentrasie was in die koeler area gevind as in die warmer area. In beide 2008 (LB en HB) en 2009 (LB) het CM die meeste antosianiene geëkstraheer, terwyl geen behandeling ‘n effek gehad het by HB. Twee van die mees populêre tannien analitiese metodes is die BSA (bovine serum albumien) en die MCP (metielsellulose presipitasie) metodes. Die BSA metode is ‘n baie meer ingewikkelde metode waarvoor drie keer meer reagense gebruik word as vir die MCP metode. Maar waar die MCP net tanniene ontleed, ontleed die BSA metode tanniene, monomere (MP), klein polimeriese pigmente (SPP) en groot polimeriese pigmente (LPP). Dit help indien daar gekyk wil word na die evolusie van polimeriese pigmente. In hierdie studie is bevind dat daar ‘n redelike korrelasie (R2 – 0.88) tussen die BSA en MCP metode bestaan. Die herhaalbaarheid van die metodes het redelike kontroversie veroorsaak, waar sommige navorsers bevind het dat die BSA metode nie so herhaalbaar is soos eers bevind is nie. Die MCP metode het ’n praktiese voordeel aangesien dit in die helfde van die tyd van die BSA metode uitgevoer kan word. Dit het ‘n groot impak indien ‘n groot hoeveelheid monsters ontleed moet word. Die fenoliese samestelling en mondgevoel word sterk beïnvloed deur die klimatologiese area. In die warmer area was die effek van tannien konsentrasie op mondgevoel kleiner as in die koeler area. Die wyn van ryper druiwe het meer harder, verdowingseffek en bitter nasmaak gehad as by die wyn van groener druiwe. Die ensiem behandeling was meer geassossieerd met droë mond gevoel.

Thesis (MScAgric (Viticulture and Oenology))--Stellenbosch University, 2008. / Soil is a component of the environment and sustains growth of several plants and animals. It forms part of the biosphere and can be described as the interface between the atmosphere and the lithosphere. The interaction between soil, climate and topography and the resulting agricultural aptitude forms the concept of terroir. This relationship is complex and it is difficult to quantify the contribution of each. Grapevines are exposed to an array of soil types. Soils have varying colours, which can be ascribed to their origin from different parent materials and pedogenetic factors. Historical and experimental evidence points to the key role that soil physical conditions play in determining grape berry composition, but other soil related factors may also play a role. This study was conducted to investigate the effect of soil surface colour on the vegetative and reproductive growth characteristics of Cabernet Sauvignon. The aim was to determine whether a relationship exists between soil colour, reflective light quality below and inside the grapevine canopy, vegetative growth of the grapevine and the berry and wine composition. The reflected light from soils was measured in three positions of the canopy and across the light spectrum (300–2500 nm) for three different soil surface treatments (black, red and grey). The effect of soil colour on vegetative parameters, yield and berry composition and wine quality was investigated. Soil surface colour resulted in differences in the reflected light quality below and in the canopy. The differences in the light quality were associated with differences in vegetative parameters such as mean main leaf, with grey soils inducing higher values. Potassium levels of the grapes and berry number per bunch appeared to be influenced by soil surface colour throughout berry development with red and black soils having higher levels of potassium and berry number per bunch than grey soils. Grape ripening parameters were not influenced by soil surface colour, but the grey treatment had a significantly more intense grape colour measured at 520 nm (red pigments). It is assumed that the importance of soil colour is its association with the physical and the pedogenetic properties that contribute to the grapevine water balance. From these results it can be concluded that soil surface colour appeared to have a direct effect on some aspects of vegetative and reproductive growth, and berry composition, but the contribution of different wavebands and mechanism of their effect deserves further study.

Thesis (MscAgric (Viticulture and Oenology))--University of Stellenbosch, 2007. / The rapid expansion of the world wine industry has increased the pressure on wine producers to produce high quality, distinguishable wines. The use of sensory evaluation alone as a tool to distinguish between wines is limited by its subjective nature. Chemical characterisation using analytical methods and data analysis techniques are increasingly being used in conjunction with sensory analysis for comprehensive profiling of wine. Analytical chemistry and chemometric techniques are important and inextricable parts of the chemical characterisation of wine. Through this process insight into the inherent composition of wines, be it in a general sense or related to a particular wine category is gained. Data generated during chemical characterisation are typically compiled into electronic databases. The application of such information towards wine quality control includes the establishment of industry benchmarks and authentication. The current project is part of The South African Young Wine Aroma Project, a long term research initiative funded by the South African Wine Industry with the ultimate aim to establish a comprehensive, up-to-date, database of the volatile composition of young wines. The data generated during this thesis represent the first contribution towards realising this ambition. Three clearly defined aims were set for this project, the first of which is the chemical characterisation of South African young wines in terms of selected volatile and non-volatile compounds and Fourier transform infrared spectra, with particular focus on the volatile composition. FTMIR spectra are information rich and non-specific instrumental signals that could provide invaluable information of the inherent composition of the wines. The second aim is the evaluation of the analytical methods used to generate the data and in the last instance, the optimisation of FTMIR spectroscopy for rapid quantification of major wine parameters and volatile compounds. The concentrations of 27 volatile compounds in South African young wines were determined by gas chromatography coupled to flame ionisation detection (GC-FID) using liquid-liquid extraction of the analytes. Wine samples of the 2005 and 2006 vintages produced from six of the most important cultivars in the South African wine industry, namely Sauvignon blanc, Chardonnay, Pinotage, Cabernet Sauvignon, Merlot and Shiraz were used. The producing cellars were from four major South African wine producing regions, namely Stellenbosch, Paarl, Robertson and Worcester. The data captured made a significant contribution to the establishment of the Aroma Project Database. Univariate statistics showed wide variations in the chemical composition of the wines. Red wines were generally characterised by high levels of higher alcohols and white wines by high levels of esters. Most of the differences between vintages were cultivar dependent and phenological differences between cultivars were suggested as a possible cause. Fusel alcohols, iso-acids and esters of fusel alcohols were particularly responsible for differences between red wines. A combination of fatty acids and higher alcohols were responsible for differences between production regions. However, using univariate statistics alone was limited in identifying characteristic features of the chemical composition of the wines. In order to explore the correlations between the volatile components, FTMIR spectra and nonvolatile components the data were further investigated with multivariate data analysis. Principal component analysis was successfully employed to distinguish between wines of different vintages and cultivars. The role of the volatile composition was more influential in the separation of vintage and red wine cultivar groupings than the non-volatile components or the FTMIR spectra. Almost all the individual volatile components contributed to the separation between the vintages and cultivars, thereby highlighting the multivariate nature required to establish the distinguishing features pertaining to each of these categories. The FTMIR spectra and the non-volatile components were more important than the volatile components to characterise the differences between the white cultivars. It was not surprising that both the volatile components and the FTMIR spectra were needed to distinguish between both red and white cultivars simultaneously. It was of interest the full spectrum, including all wavenumbers were required for a powerful classification model. This finding supports the initial expectation that the non-selective but information rich signal captured in the FTMIR spectra is indispensable. No distinction could be made between the production regions, which was not surprising since the wines used in this study was not of guaranteed origin. Furthermore, no clear correlation could be established between the chemical composition or the FTMIR spectra and the quality ratings of the wines. Limitations in the dataset were pointed out that must be taken into account during further investigations in the future. The liquid-liquid extraction method used during the analysis of the volatile components was evaluated for precision, accuracy and robustness. Generally good precision and accuracy were observed. There were slight indications of inconsistencies in the recoveries of analytes between the red and white wine matrices. Certain parameters of the protocol, namely sample volume, solvent volume, sonication temperature and sonication time, were identified as factors that had a major influence on quantification. The results obtained in this study made a major contribution towards establishing this technique for routine GC-FID analysis in our environment. Due to the high sample throughput in wine laboratories, the use of rapid quantitative analytical methods such as FTMIR spectroscopy is becoming increasingly important. Enzymatic-linked spectrophotometric assays and high performance liquid chromatography (HPLC) methods were evaluated for their suitability to serve as reference methods for optimising and establishing FTMIR calibrations for glucose, fructose, malic acid, lactic acid and glycerol. Pigmented and phenolic compounds were identified as sources of interference in the determination of organic acids in red wines with both enzymatic assays and HPLC. The use of fining treatments for the decolourisation of red wine samples was investigated. Activated charcoal was more efficient in terms of colour removal than polyvinyl polypyrrolidone (PVPP), but neither were compatible with the specific enzymatic method used in this study. Solid phase extraction (SPE), a method commonly used during sample clean-up prior to HPLC analysis of organic acids in wine, and PVPP fining were evaluated as sample preparation methods for HPLC analysis to optimise the quantification of organic acids in red wine. Four different types of SPE cartridges were evaluated and the SPE method was optimised in order to recover the maximum amount of organic acids. However, low recoveries, in some instance less than 50%, for the organic acids in wine were reported for the optimised SPE method. In this respect one was the worst. On average, excellent recoveries were observed for the organic acids using the PVPP method that were in excess of 90%. This method therefore provides a very valuable and simple alternative to SPE for sample-cleanup prior to HPLC analysis. One aspect that still needs to be investigated is the reproducibility of the method that should still be optimised. In general, enzymatic analysis was more suitable for the determination of glucose and fructose, while HPLC analysis were more suitable for the quantification of organic acids. Efficient glycerol quantification was observed with both enzymatic and HPLC analysis, although a lower measurement error was observed during the HPLC analysis. Apart from reliable reference methods, successful FTMIR calibrations also rely on the variability present in the reference sample set. The reference sample set used to establish FTMIR calibrations must ideally be representative of the samples that will be analysed in the future. Commercial, or so-called global, FTMIR calibrations for the determination of important wine parameters were evaluated for their compatibility to a South African young wine matrix. The prediction pH, titratable acidity, malic acid, glucose, fructose, ethanol and glycerol could be improved by establishing a brand new FTMIR calibration, thereby clearly indicating that the South African young wine matrices were significantly different from the samples of European origin that were used to establish the commercial calibrations. New preliminary calibration models were established for a young wine sample matrix and were validated using independent test sets. On average the prediction errors were considered sufficient for at least screening purposes. The effect of wavenumber selection was evaluated. Relatively successful models could be established for all the compounds except glucose. Wavenumber selection had an influence on the efficiency of the calibration models. Some models were more effective using a small amount of highly correlated wavenumbers, while others were more effective using larger wavenumber regions. Preliminary FTMIR calibration models for the screening of volatile compound groups in young wines were evaluated. Compound groups were compiled based on chemical similarity and flavour similarity. Good linearity were observed for the “total alcohol”, “total fatty acids”, “esters” models while an interesting polynomial trend was observed for the “total esters” model. Relatively high prediction errors indicated the possibility of spectral interferences, but the models were nevertheless considered suitable for screening purposes. These findings are a valuable contribution to our environment where fermentation flavour profiles must often be examined. The important role sound and validated analytical methods to generate high quality analytical data, and the subsequent application of chemometric techniques to model the data for the purpose of wine characterisation has been thoroughly explored in this study. After a critical evaluation of the analytical methods used in this study, various statistical methods were used to uncover the chemical composition of South African young wines. The use of multivariate data analysis has revealed some limitations in the dataset and therefore it must be said that wine characterisation is not just reliant on sophisticated analytical chemistry and advanced data analytical techniques, but also on high quality sample sets.