Thesis (MscAgric (Viticulture and Oenology))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Tannins and colour components in red wine are important quality parameters. These factors can
be manipulated in the vineyard by grape growing techniques or in the cellar by different winemaking
practices. Grape seeds make a significant contribution to tannin concentration in wine
when compared to those from the skins and pulp. Tannins contribute to the ageing potential,
organoleptic properties and stabilisation of red wine colour. The colour of a red wine is also
influenced by malolactic fermentation, the biological process that transforms malic acid into
lactic acid which normally leads to an increase in pH. The subsequent change in pH alters the
anthocyanin equilibrium, the primary colour components in red wine. Oxygen contributes to the
polymerisation of anthocyanins over time to form more stable pigments that are less sensitive to
pH fluctuations and sulphur dioxide bleaching. Limited research has been done on the use of
oxygen after alcoholic fermentation and the impact it has on the phenolic composition of red
wines. Similarly, only a few studies have examined the impact of either the addition or removal
of seeds to the phenolic composition of a red wine in combination with oxygen addition.
Additionally, little published data seems to exist on the effect of different pHs on red wine’s
phenolic and colour development after oxygen addition.
In our results we have shown that it is possible to stabilise wine colour by adding
supplementary seeds before alcoholic fermentation. This led to an increase in colour intensity in
certain cases. Some red wines produced without seeds had significantly lower colour intensities.
This clearly suggests that catechins and proanthocyanidins are extracted from seeds and
contribute to wine colour as they combine with other pigments to stabilise wine colour.
Spectrophotometric and HPLC analyses have shown that the total phenolic content increased
with seed concentration. However, we have observed that a wine may possibly become
saturated with phenols when supplementary seeds are added. Anthocyanin concentrations
often decreased when oxygen was added, while polymeric phenols and polymeric pigments
sometimes increased.
When applying different oxygen dosages to a red wine on commercial scale with microoxygenation,
it was found that monomeric anthocyanins decreased as more oxygen was added
and this decrease in anthocyanins led to the formation of stable polymeric pigments. This
was reflected in the significant increase in colour intensity for the wines receiving oxygen. Small
differences were detected in the total phenol and tannin concentration for the control and
oxygenated wines. However, some of these phenolic and colour differences disappeared
during subsequent ageing of the wine.
When making wines of different initial pHs, we observed that the colour density decreased
as the pH increased. The application of oxygen reduced the decrease in colour during MLF,
especially at a lower pH. The addition of oxygen did not result in significantly different polymeric
pigment concentrations in the various pH treatments, although the results could have been
different if the wines were aged. However, pH differences in the range between 3.4 and 4.0 did
not significantly influence the phenol composition of the wines under our conditions. This study
led to a better understanding on the effect of oxygen additions under different conditions on red
wine's phenolic and colour composition. / AFRIKAANSE OPSOMMING: Tanniene en kleur komponente teenwoordig in rooiwyn is belangrike kwaliteit parameters.
Hierdie faktore wat wynkwaliteit beïnvloed kan gemanipuleer word in die wingerd deur verskeie
verbouingstegnieke toe te pas en in die kelder deur die toepassing van verskillende
wynbereidingsmetodes. Die bydrae van sade tot die finale tannienkonsentrasie in rooiwyn is
groot in vergelyking met dié van die pulp en doppe. Tanniene dra by tot die verouderingspotensiaal,
organoleptiese eienskappe en die stabilisasie van die wynkleur. Die kleur van ‘n rooi
wyn word ook beïnvloed deur appelmelksuurgisting (AMG), die biologiese proses wat appelsuur
omskakel na melksuur en ‘n gevolglike toename in die pH van die wyn veroorsaak. Hierdie
verandering in die pH van die wyn beïnvloed die antosianien ewewig, die primêre kleur
komponente teenwoordig in rooiwyn. Suurstof dra by tot die polimerisasie van antosianiene oor
tyd om meer stabiele kleur pigmente te vorm met ‘n hoër kleurintensiteit wat minder sensitief is
teenoor pH veranderinge en die bleikingseffek van swaweldioksied. Beperkte navorsing is
gedoen op die gebruik van suurstof na alkoholiese gisting en die impak daarvan op die
fenoliese samestelling van ‘n rooiwyn. Slegs ‘n paar studies het die invloed van die verwydering
of byvoeging van sade in kombinasie met suurstoftoediening op ‘n rooiwyn se fenoliese
samestelling ondersoek. Dit wil voorkom of beperkte gepubliseerde data beskikbaar is oor die
effek wat verskillende pH’s het op rooi wyn se fenoliese en kleurontwikkeling na suurstof
byvoeging.
Ons resultate het aangedui dat dit wel moontlik is om in sekere gevalle die kleur van ‘n
rooiwyn te stabiliseer deur addisionele sade by te voeg voor alkoholiese fermentasie. Hierdie
byvoeging het ‘n toename in kleurintensiteit tot gevolg gehad. Sekere wyne wat gemaak is
sonder sade het ‘n kenmerkend laer kleur intensiteit gehad. Hierdie bevinding is ‘n duidelike
bewys dat katesjiene en prosianidiene geëkstraheer word vanuit die sade en bydra tot wynkleur
deurdat hulle met ander pigmente verbind om die kleur sodoende te stabiliseer.
Spektrofotometriese en hoë druk vloeistof chromatografie (HDVC) analises het gewys dat die
totale fenoliese konsentrasie neem toe met ‘n toename in saad konsentrasie. Daar is egter
waargeneem dat ‘n wyn moontlik versadig kan raak met fenole wanneer addisionele sade
bygevoeg word. Antosianien konsentrasies het meestal afgeneem wanneer suurstof bygevoeg
is, maar polimeriese fenole en polimeriese pigmente het partykeer toegeneem.
Met die toediening van verskillende suurstof dosisse tot ‘n rooiwyn op kommersiële skaal
het ons bevind dat monomeriese antosianiene afneem wanneer meer suurstof bygevoeg word.
Hierdie afname in antosianiene het egter gelei tot die vorming van stabiele polimeriese
pigmente. Dié bevinding was gereflekteer in die toename in kleurintensiteit van wyne wat met
suurstof behandel is. Klein verskille was waargeneem vir die totale fenol en tannien
konsentrasies tussen die kontrole en wyne behandel met suurstof. Sekere van hierdie fenoliese
kleur verskille het egter afgeneem tydens die daaropvolgende veroudering van die wyne.
Wyne wat gemaak is met verskillende aanvanklike pH’s se kleurintensiteit neem af soos
die pH toeneem. Die toediening van suurstof het die kleurverlies tydens AMG verminder, veral
by ‘n laer pH. Die toediening van suurstof het nie verskillende polimeriese pigment
konsentrasies by verskillende pH’s veroorsaak nie, maar ‘n verskil kon moontlik waargeneem
word indien die wyne verouder was. pH verskille tussen 3.4 en 4.0 het egter nie die fenoliese
samestelling van die wyne onder ons omstandighede beduidend beïnvloed nie. Hierdie studie
het gelei tot meer kennis oor die effek van suurstoftoedienings onder verskillende kondisies op
rooiwyn se fenoliese en kleursamestelling.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1611 |
| Date | 12 1900 |
| Creators | Geldenhuys, Lorraine |
| Contributors | Du Toit, W. J., Oberholster, A., University of Stellenbosch. Faculty of Agrisciences. Dept. of Viticulture and Oenology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Rights | University of Stellenbosch |
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