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.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6872 |
| Date | 03 1900 |
| Creators | Nel, Anton Pieter |
| Contributors | Lambrechts, Marius, Van Rensburg, Pierre, 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 |
| Format | 146 p. : ill. |
| Rights | University of Stellenbosch |
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