Grape and wine phenolic composition as a result of training system and canopy modification in Vitis vinifera L.cv Shiraz.

De Beer, Petrus Johannes (2015-12)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Non-volatile phenols, such as anthocyanins and tannins, are important parameters used in measuring the quality of red wine, as they are the main components influencing red wine colour and astringency. The Smart-Dyson (SD) training system, as developed by Dr Richard Smart and John Dyson, has previously been investigated as an alternative to the vertical shoot positioning (VSP) training system for vigorous vines, as it has the effect of bringing the vine “into balance” and has been shown to increase grape yield. The effects of the SD training system on the non-volatile phenols of the grapes, and how these treatment differences influence the wine, have been investigated in international studies, but limited studies have been done under South African conditions. The first aim of this study was to assess differences in the non-volatile phenol composition of Shiraz grapes at harvest originating from a Reduced, VSP or SD training system and to assess whether these differences are reflected in the wines between treatments. Between these selected treatments it was found through spectrophotometer and HPLC analysis that the SD system may sometimes lead to a lower concentration of phenols in wine, although the physical structure of the SD system is expected to be more conducive to a better microclimate to enhance the phenolic concentration. The reduced treatment was also added, as it is a method for reducing vegetative growth by physically removing vegetative matter from the plant. This also leads to a better microclimate, but may have a negative effect on the yield. The second aim of the study was to examine how the differences between the reduced, SD- and VSP treatments in wine were affected by ageing. The reaction rates of the different non-volatile phenols differ and thus their interaction during wine ageing might differ. This will affect the ageing potential, depending on the relative concentrations of the different phenols. However, the relative differences between the treatments remained unchanged during ageing. The final aim of this study was to look at whether the treatment differences in the wine could be perceived sensorially. As sensory perception is ultimately the main parameter by which wine quality is judged by the consumer, it is important to know if analytical differences are reflected sensorially. When the wines were tasted, the panel could in general not find an association between the treatments. The results generated from this study show that there were some differences regarding non-volatile phenols between the, Reduced canopy treatment and SD- and the VSP training system treatments. It still has to be investigated how management practices relating to these training systems can affect these differences.

AFRIKAANSE OPSOMMING: Nie-vlugtige fenole, soos antosianiene en tanniene, is belangrike parameters wat gebruik word om die kwaliteit van rooi wyn te meet, aangesien hulle die vernaamste komponente is wat ’n invloed op die kleur en vrankheid van rooi wyn het. Die Smart-Dyson (SD) opleistelsel, wat deur dr Richard Smart en John Dyson ontwikkel is, is reeds as ’n alternatief tot die vertikale loot posisionering (VSP) stelsel vir geil wingerdstokke ondersoek, aangesien die effek daarvan is om die wingerdstok in balans te bring en daar is ook getoon dat dit druif opbrengs verhoog. Die invloed van die Smart-Dyson stelsel op die nie-vlugtige fenole van die druiwe, en hoe hierdie verskille die wyn beïnvloed, is reeds in internasionale studies ondersoek, maar daar is beperkte studies daaroor onder Suid-Afrikaanse toestande. Die eerste doelwit van hierdie studie was dus om die verskille in die nie-vlugtige fenol samestelling van Shiraz-druiwe afkomstig van ’n VSP- of SD-opleistelsel te ondersoek en hoe hierdie verskille in die wyne weerspieël word. Tussen die gekose behandelings van ʼn verminderde behandeling, kontrole VSP en Smart-Dyson behandeling is daar gevind dat die SD-stelsel soms kan lei tot ’n laer konsentrasie van fenole deur spektrofotometriese en HLPC analises, hoewel die struktuur van die SD-stelsel veronderstel is om voordelig te wees vir ’n beter mikroklimaat, wat die fenol konsentrasie sal verhoog. Die verminderde behandeling is ook ingesluit, aangesien dit ’n metode is waarvolgens vegetatiewe groei verminder kan word deur vegetatiewe materiaal fisies van die plant te verwyder. Dit lei ook tot ’n beter mikroklimaat, maar het moontlik ’n negatiewe effek op die opbrengs. Die tweede doelwit van die studie was om te ondersoek hoe die verskille tussen die SD- en VSPbehandelings deur veroudering beïnvloed word. Die reaksietempo’s van die verskillende nie-vlugtige fenole verskil, en dit is dus moontlik dat hulle interaksie tydens wynveroudering ook sal verskil. Dit sal die verouderingspotensiaal beïnvloed op grond van die relatiewe konsentrasies van die verskillende fenole. Daar is wel gevind dat die relatiewe verskille tussen die behandelings dieselfde gebly het met veroudering. Die finale doelwit van die studie was om ondersoek in te stel na die moontlikheid dat die verskille tussen die behandelings sensories waargeneem kan word. Aangesien sensoriese persepsie die uiteindelike parameter is waarvolgens wyn deur die verbruiker beoordeel word, is dit belangrik om te weet of analitiese verskille sensories weerspieël word. Toe die wyne geproe is kon die paneel nie tussen die behandelings onderskei nie. Die resultate wat deur hierdie studie gegenereer is, wys dat daar verskille is met betrekking tot nievlugtige fenole tussen die SD- en die VSP-opleistelsels. Daar moet nog ondersoek word hoe bestuurspraktyke wat verband hou met hierdie opleistelsels hierdie verskille kan beïnvloed.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98126
This item appears in the following collections: