Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Phenolic compounds are important quality indicators of a red wine, as they can contribute to the
colour of a young red wine, colour stability during ageing as well as astringency, bitterness,
body and overall mouthfeel properties. Wine composition is commonly influenced by
winemaking and viticultural practices.
In South Africa it often happens that vines are excessively vigorous, resulting in canopies
that are too dense, which in turn could have a negative effect on the quantity and quality of the
grapes produced. Viticultural practices such as judicious canopy management and irrigation are
designed to control vine vigour and yield, thus improving fruit ripening and colour development.
Artificial shading and water deficit have been reported to have an influence on the sensory
properties of red wine as well as on the flavonoid composition. These effects are dependent on
a number of factors, however, including the season, cultivar, light intensity, and the extent and
timing of water deficit.
There is limited research on the possible interactive effects of grapevine water deficits and
canopy manipulation on grape and wine flavonoid composition in Shiraz, as well as the
relationships between berry and wine composition. We thus investigated the effect of canopy
reduction in combination with water deficit on the phenolic and colour composition of Shiraz
grapes at different levels of ripeness, and in their corresponding wines after alcoholic and
malolactic fermentation as well as after six months’ ageing. This study found that it is possible to
improve the phenolic composition of grapes and wine by shoot removal, and some of the
tendencies in the wines were also observed after the ageing period. If the shoot removal is not
performed at a very early stage, sunburn damage can occur and this will result in berries with a
lower mass and volume at harvest due to excessive exposure without the berry having adapted
to the imposed conditions.
Harvesting at different ripeness levels also affected the chemical and phenolic composition
of the grapes and resulting wines. The water deficit effect on most phenolic parameters
measured in the grapes and wine was not as prominent as that of the canopy manipulation
treatment.
This study improved our understanding of how an improvement in the canopy microclimate
of Shiraz could be reflected in the phenolic composition of wines, along with a potentially
important effect of harvesting date. On this basis it may be possible to attain a specific wine
style. Harvesting at a ripe stage, for example, could result in the production of wines with higher
colour density and astringency, while unripe grapes could result in wines with higher levels of
perceivable fresh berry attributes. In particular, canopy reduction could increase the astringency
and body of wines made from grapes subjected to water deficit. / AFRIKAANSE OPSOMMING: Fenoliese verbindings is belangrike kwaliteitsparameters van rooiwyn, aangesien dit kan bydra
tot die kleur van ‘n rooiwyn, kleurstabiliteit tydens veroudering sowel as frankheid, bitterigheid
en mondgevoel. ‘n Wyn se fenoliese samestelling word algemeen bepaal deur wynmaak- en
wingerdkundige praktyke.
In Suid-Afrika gebeur dit gereeld dat wingerde uitermatig groeikragtig is, wat lei tot te digte
lower wat sodoende ‘n negatiewe effek op kwantiteit en kwaliteit van die druiwe wat
geproduseer word, het. Wingerdkundige praktyke soos oordeelkundige lowerbestuur en
besproeiing is ontwerp om wingerdstokke se groeikrag en opbrengs te beheer, en sodoende
vrugrypwording en kleurontwikkeling te verbeter.
Kunsmatige beskaduwing en waterstres is gerapporteer om ‘n invloed te hê op die
sensoriese eienskappe van rooiwyn sowel as op die flavonoïedsamestelling. Hierdie effekte is
egter afhanklik van ‘n verskeidenheid faktore, insluitende die seisoen, kultivar, ligintensiteit en
die mate en tyd van waterstres toegepas.
Daar is beperkte navorsing op die moontlike interaktiewe effekte van waterstres en
lowermanipulasie op die druif en wyn flavonoïedsamestelling in Shiraz, sowel as die
verhoudings tussen druif en wyn samestelling. Ons het dus die effekte van lowerbestuur in
kombinasie met waterstres op die fenoliese en kleursamestelling van Shiraz druiwe by
verskillende rypheidsvlakke ondersoek, asook in hul ooreenstemmende wyne na alkoholieseen
appelmelksuurfermentasie sowel as na ses maande veroudering. Hierdie studie het gevind
dat dit moontlik is om die fenoliese samestelling van druiwe en wyn deur lootverwydering te
verbeter, en sommige van die tendense is ook waargeneem in die wyn na die
verouderingsperiode. Indien lootverwydering nie toegepas word by ‘n baie vroeë stadium nie,
kan sonbrand voorkom en dit kan lei tot korrels met ‘n laer massa en volume by oes as gevolg
van oormatige blootstelling sonder dat die korrel aangepas het by die spesifieke kondisies.
Oes by verskillende rypheidsvlakke affekteer ook die chemiese en fenoliese samestelling
van die druiwe en ooreenstemmende wyne. Die waterstreseffek op meeste van die fenoliese
parameters gemeet in druiwe en wyn was nie so prominent soos dié van die lowermanipulasie
behandeling nie.
Hierdie studie het ons begrip verbeter van hoe ‘n verbetering van die lower mikroklimaat
van Shiraz gereflekteer kan word op die fenoliese samestelling van die wyn, saam met ‘n
potensiële belangrike effek van oesdatum. Op grond van hierdie basis is dit dus moontlik om ‘n
spesifieke wynstyl te verkry. Oes by ‘n ryp stadium, byvoorbeeld, kan die produksie van wyn
met ‘n hoër kleurdigtheid en frankheid tot gevolg hê, terwyl onryp druiwe wyne met hoër vlakke
van waarneembare vars bessiekenmerke tot gevolg kan hê. Verlaging van lowerdigtheid kan
veral die frankheid en mondgevoel van wyne gemaak van druiwe blootgestel aan waterstres,
verbeter.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71763 |
| Date | 12 1900 |
| Creators | Van Noordwyk, Marelize |
| Contributors | Du Toit, W. J., Strever, A. E., Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 108 p. : ill. (some col.) |
| Rights | Stellenbosch University |
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