Thesis (MScAgric)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Ferdinand de Lesseps grapes have a distinctive fruity varietal character and were often used
judiciously by wine-makers to enhance the fruity bouquet of some white table wines.
Ferdinand de Lesseps grape juice was investigated to identify the main contributing
compounds responsible for its unique and intense aroma. The juice was recovered from
grapes under anaerobic conditions and extracted using Freon 11. The concentrated extract was
analysed using a combination of capillary gas chromatography-mass spectrometry and gas
chromatography-sniffing techniques. Thirty-two compounds were reported. With the aid of
GC-sniffing, it was concluded that the hybrid note of the Ferdinand de Lesseps grape was
most likely attributed to the presence of 2,5-dimethyl-3(2H)-furanone and 0-
aminoacetophenone. Esters, which featured prominently in the juice, consisted mainly of
ethyl butanoate, ethyl- and methyl- 3-hydroxy butanoate, and to a lesser extent, ethyl 3-
hydroxy hexanoate and ethyl-3-hydroxy propanoate. These esters are most likely responsible
for the sweetish pineapple aroma. According to EEC regulations, the use of non- Vinifera
grapes in the production of commercial wines is prohibited. The presence of 2,5-dimethyl-
3(2H)-furanone in wine could therefore be interpreted as a labrusca indicator should it be
suspected that Ferdinand de Lesseps grapes were used in the blend.
The quality of some South African Kerner table wines often is rated inferior owing to an
unwanted odour described as "Elastoplast" or "medicinal". This odour is encountered
occasionally in wines from other cultivars such as Gewurztraminer, Weisser Riesling, Muscat
de Frontignan and Chenin blanc. The identification of the compounds responsible for the offodour
was investigated, as well as possible relationships between its occurrence and viniviticultural
practices. The compound responsible for the "medicinal" off- odour was identified as p-vinyl guaiacol. It is formed via decarboxylation of ferulic acid by yeast during alcoholic
fermentation. lts concentration is directly related to the concentration of ferulic acid and the
yeast strain. Other factors affecting p-vinyl guaiacol formation in Kerner wines are region,
microclimate, exposure of grapes to sunlight and grape maturity. Wines made from grapes
harvested from the warmer climatic regions and exposed to direct sunlight and increased
maturity contained higher levels of p-vinyl guaiacol. Viticultural practices that can be applied
to limit the formation of the p-vinyl guaiacol precursor in grapes are the use of a canopy
manipulation to protect the grapes from direct sunlight and an earlier harvesting date.
Various winemaking techniques can be used to lower p-vinyl guaiacol levels in wine. Careful
consideration must be given to the choice of yeast, as different yeast strains differ
considerably with their ability to form p-vinyl guaiacol. Fining oxidised grape juice with
phenol adsorbing agents such as activated charcoal, polyvinylpolypirrollidone, casein, gelatin
(particularly in combination with bentonite and "kieselsol") led to decreases in the p-vinyl
guaiacol levels. Although fining with activated charcoal was the most effective must
treatment for reducing the "medicinal" aroma of Kerner wines, it stripped the wines of colour
and character. Excessive oxidation of must followed by fining involves extra costs and time
for the winemaker and would not be used in making the reductive style of wines. / AFRIKAANSE OPSOMMING: Ferdinand de Lesseps druiwe en wyne vertoon unieke vrugtige varieteitskarakter en is dikwels
deur wynmakers in versnitte gebruik om die geur van sekere wit tafelwyne te verbeter. In
hierdie studie is Ferdinand de Lesseps druiwe ondersoek om die belangrikste komponente wat
verantwoordelik is vir die prominente, unieke aroma daarvan te identifiseer. Die sap is onder
anaerobe toestande herwin en met Freon 11 ekstraheer. Die gekonsentreerde ekstrakte is met
behulp van 'n kombinasie van kapillêre gaschromatografie-massaspektrometrie en
gaschromatografie-snuif tegnieke analiseer. Twee-en-dertig komponente is gerapporteer. Met
die behulp van GC-snuiftegnieke is bevestig dat die hibried karakter in Ferdinand de Lesseps
druiwe hoofsaaklik aan die teenwoordigheid van o-amino-asetofenoon en 2,5-dimetiel-3(2H)-
furanoon toegeskyf kan word. Die vernaamste esters in die sap was etielbutanoaat, etiel- en
metiel-3-hidroksibutanoaat en in 'n mindere mate etiel-3-hidroksiheksanoaat en etiel-3-
hidroksipropanoaat. Dié esters is waarskynlik verantwoordelik vir die soet pynappel aroma.
Volgens EEG regulasies word die gebruik van nie- Vinifera druiwe vir die produksie van
komersiéle wyne verbied. Die teenwoordigheid van 2,5-dimetiel-3(2H)-furanoon in wyn kan
dus interpreteer word as 'n labrusca indikator in gevalle waar gebruik van Ferdinand de
Lesseps druiwe vermoed word.
Die kwaliteit van sommige Suid-Afrikaanse Kerner wyne word dikwels verlaag vanweë die
teenwoordigheid van 'n geur wat beskryf word as "Elastoplast" of "medisinaal". Dié reuk
word soms waargeneem in wyne van ander kutivars soos Gewurztraminer, Weisser Riesling,
Muskaat de Frontignan en Chenin blanc. Die identiteit van die komponent wat vir dié
ongewenste reuk verantwoordelik is, asook moontlike verwantskappe met wingerd- en
wynkundige praktyke is ondersoek. Die komponent wat vir die medisinale karakter
verantwoordelik is, is geïdentifiseer as para-vinielguajakol. Dit word deur dekarboksilasie van feruliensuur deur gisselle tydens alkoholiese gisting gevorm. Die konsentrasie van paravinielguajacol
in wyn is direk verwant aan die konsentrasie feruliensuur en die gisras. Ander
faktore wat para-vinielguajacol-vorming in Kerner wyn affekteer is streek, mikroklimaat,
blootstelling van druiwe aan direkte sonlig en die rypheidsgraad van die druiwe. Wyne wat
berei is van ryper druiwe uit warmer streke en wat direk aan sonlig blootgestel was, het hoër
konsentrasies para-vinielguajacol bevat. Lowerbestuurspraktyke met behulp waarvan druiwe
teen direkte sonligblootstelling beskerm word, is van die vernaamste wingerdkundige
praktyke wat aangewend kan word om die vorming van die voorlopers van paravinielguajacol
in druiwe te verlaag.
Verskeie wynbereidingstegnieke kan gebruik word om die para-vinielguajacol vlakke in wyn
te verlaag. Gisraskeuse is van besondere belang omdat gisrasse grootliks verskil in hul
vermoë om para-vinielguajacol te vorm. Breibehandelings van geoksideerde sap met middels
soos geaktiveerde koolstof, PVPP, kasseïen, gelatien (veral in kombinasie met bentoniet en
"kieselsol") het die vlakke van para-vinielguajacol in wyne verlaag. Hoewel geaktiveerde
koolstof die doeltreffendste breimiddel vir die verlaging van para-vinielguajacol was, het dit
te veel kleur en geur uit die wyn verwyder. Oormatige oksidasie van mos gevolg deur
breibehandelings sal meer geld en tyd verg en word nie aanbeveel vir wyne wat in 'n
reduktiewe styl berei word nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51911 |
| Date | 03 1900 |
| Creators | Rogers, Ilva Margaret |
| Contributors | Van Wyk, C. J., Goussard, P. G., Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology. Institute for Wine Biotechnology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 46 p. |
| Rights | Stellenbosch University |
Page generated in 0.01 seconds