Dissertation (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Wine is the product of a complex biological and biochemical interaction between
grapes and different microorganisms (fungi, yeasts, lactic acid bacteria and acetic
acid bacteria, as well as the mycoviruses and bacteriophages affecting them) in
which yeasts play the most important role regarding the alcoholic (primary)
fermentation. These wine-associated yeasts can be divided into Saccharomyces and
non-Saccharomyces yeasts. During fermentation, there is a sequence of dominance
by the various non-Saccharomyces yeasts, followed by Saccharomyces cerevisiae,
which then completes the fermentation. This is especially evident in spontaneously
fermenting must, which has a low initial S. cerevisiae concentration. Some non-
Saccharomyces yeasts can also be found throughout the fermentation. The non-
Saccharomyces presence in the fermentation can affect wine quality, either positively
or negatively. A positive contribution could be especially useful to improve wines
produced from grape varieties with a neutral flavour profile due to non-optimal
climatic conditions and/or soil types. As part of a comprehensive South African
research programme, the specific objectives of this study were: the isolation of
indigenous non-Saccharomyces yeasts from vineyards and musts; the identification
of these isolates; the characterisation and evaluation of predominant species under
winemaking conditions; and the development of a protocol for their use in enhancing
wine quality.
Initially, 720 isolates representing 24 different species, were isolated from grape
(vineyard) and must samples taken over three vintages from four distinctly different
wine producing regions. The isolates were characterised and grouped utilising
biochemical profiles and DNA karyotyping, whereupon representative isolates were
identified. The yeast species that had the highest incidence of predominance in the
vineyard was Kloeckera apiculafa. However, some vineyard samples were
characterised by low numbers or absence of this yeast, which is not according to
generally accepted norms. Other species that also predominated in a few of the
vineyard samples were Candida pulcherrima, Kluyveromyces thermofolerans,
Rhodotorula sp. and Zygosaccharomyces bailii. Generally, there was a greater
diversity of yeasts in the processed must than from the vineyard samples. Furthermore, while each sample showed a different yeast population, no pattern
linking species to climatic zone was observed.
Four species i.e. Candida collieulosa, Candida pulcherrima, Candida stel/ata and
Kloeckera apiculata, were found to predominate in grape must samples.
Representative strains consequently received further attention during laboratory and
small-scale winemaking trials. A protocol was developed whereby individual species
could be used in co-inoculated fermentations with S. cerevisiae in the small-scale
production of wine. An improvement in wine quality was achieved and it was found
that there was a link between specific species and grape cultivar. The ability of
C. pulcherrima to improve Chenin blanc wine quality was investigated further. Results
over three vintages showed that the wine produced by the co-inoculated fermentation
was superior to that of a reference wine (produced by S. cerevisiae only). The
improvement in wine quality was not linked to increased ester content nor were the
standard chemical analyses adversely affected. The effects of pH and wine
production parameters i.e. 802, fermentation temperature and use of di-ammonium
phosphate (DAP), on this yeast followed the same pattern as that known for
S. cerevisiae. This study was successfully completed and the developed protocol can
be used for the improvement of Chenin blanc wine where additional aroma and
quality is needed. / AFRIKAANSE OPSOMMING: Wyn is die produk van 'n komplekse biologiese en biochemiese interaksie tussen
druiwe en mikroorganismes (swamme, giste, melksuurbakterieë, asynsuurbakterieë,
asook die mikovirusse en bakteriofage wat hul beïnvloed) waar gis die belangrikste
rol speel ten opsigte van die alkoholiese (primêre) fermentasie. Die betrokke giste
kan in Saccharomyces- en nie-Saccharomyces-giste verdeel word. Tydens gisting
vind daar 'n opeenvolging van dominansie deur die verskillende nie-Saccharomyces
giste plaas, gevolg deur Saccharomyces cerevisiae, wat dan die gisting voltooi. Dit is
veral in spontaan fermenterende mos, waarin aanvanklik lae konsentrasies
S. cerevisiae-gisselle voorkom, waarneembaar. Sekere nie-Saccharomyces-giste
kan ook regdeur die verloop van fermentasie gevind word. Die teenwoordigheid van
nie-Saccharomyces-giste kan 'n bydrae maak tot wynkwaliteit, hetsy positief of
negatief. 'n Positiewe bydrae kan veral nuttig wees vir die verbetering van wyn
geproduseer van druifsoorte met neutrale geurprofiele as gevolg van nie-optimale
klimaatstoestande en/of grondtipes. As deel van 'n uitgebreide Suid-Afrikaanse
navorsingsprogram, was die doelwitte van hierdie studie soos volg: die isolasie van
inheemse nie-Saccharomyces-giste vanuit wingerde en mos; die identifikasie van
hierdie isolate; die karakterisering en evaluering van spesies wat tydens
wynbereiding oorheers; en die ontwikkeling van 'n protokol waarin geselekteerde nie-
Saccharomyces-giste gebruik kan word vir die verbetering van wynkwaliteit.
Druif- en mosmonsters is oor drie oestye vanuit vier duidelik onderskeibare
wynproduserende gebiede geneem en 720 isolate, verteenwoordigend van 24
verskillende spesies, is hieruit geïsoleer. Hierdie isolate is volgens biochemiese
profiele en DNA-kariotipering gekarakteriseer en gegroepeer waarna
verteenwoordigende isolate geïdentifiseer is. Die gisspesie wat die meeste in
wingerde voorgekom het, was Kloeckera apiculata. Sommige wingerde is egter deur
lae getalle of afwesigheid van dié gis gekenmerk, In feit wat afwyk van die algemeen
aanvaarde norm. Ander spesies, nl. Candida pulcherrima, Kluyveromyces
thermotolerans, Rhodotorula sp. en Zygosaccharomyces bailii, het ook in enkele
gevalle in die wingerdmonsters oorheers. Oor die algemeen was daar 'n groter
diversiteit van giste in die geprosesseerde mos as in die wingerdmonsters. Verder is elke monster gekenmerk deur verskillende gispopulasies, maar geen verband tussen
gisspesie en klimaatsone is waargeneem nie.
Vier spesies, nl. Candida collieulosa, Candida pulcherrima, Candida stel/ata en
Kloeckera apiculata, het in hoë getalle in die druiwemosmonsters oorheers en
verteenwoordigende rasse het verdere aandag tydens laboratorium- en kleinskaalse
wynmaakproewe geniet. 'n Protokol, waar hierdie rasse individueel gebruik is in
gesamentlike geïnokuleerde fermentasies met S. cerevisiae vir die kleinskaalse
produksie van wyn, is ontwikkel. 'n Verbetering in wynkwaliteit is verkry en daar is 'n
verband tussen spesifieke gisspesies en druifvariëteit gevind. Gevolglik is die vermoë
van C. pulcherrima om die gehalte van Chenin blanc wyn te verbeter, verder
ondersoek.
Resultate oor drie oesjare het gewys dat die wyn wat met die C. pulcherrima /
S. cerevisiae kombinasie geproduseer is, beter was as 'n verwysingswyn (deur slegs
S. cerevisiae geproduseer). Die waargenome verbetering in wynkwaliteit was egter
nie aan 'n verhoging in esterinhoud te danke nie en die standaard chemiese analises
het geen negatiewe afwyking uitgewys nie. Verder is gevind dat die effek van pH en
wynproduksieparameters, nl. die gebruik van S02, fermentasietemperatuur en die
gebruik van di-ammoniumfosfaat (DAP), dieselfde patroon as die bekend vir
S. cerevisiae gevolg het. Die ontwikkelde protokol kan nou aangewend word waar
verhoogde Chen in blanc wynaroma en kwaliteit verlang word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/49877 |
| Date | 03 1900 |
| Creators | Jolly, N. P. (Neil Paul) |
| Contributors | Pretorius, I. S., Augustyn, O. P. H., 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 | 170 p. : ill. |
| Rights | Stellenbosch University |
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