| Summary: | Thesis (MScAgric)--Stellenbosch University, 2013. === ENGLISH ABSTRACT: The influence of malolactic fermentation (MLF) in most red and some white wines is one of
many factors that determine or influence wine quality, because it affects the flavour and sensory
profile of wine. This process is a decarboxylation process conducted by lactic acid bacteria
(LAB) such as Oenococcus, Lactobacillus, Pediococcus and Leuconostoc. Mostly
Oenococcus oeni, but recently also Lactobacillus plantarum is used in commercial starter
cultures and also the first mixed MLF starter culture (NT 202 Co-Inoculant) was commercialized
in 2011. The reason for the predominant use of O. oeni and recently L. plantarum is due to their
tolerance to the harsh wine environment.
Malolactic fermentation leads to a decrease in acidity and an increase in pH that leaves the
wine with a softer mouthfeel. Another reason to conduct MLF is the improvement of microbial
stability by the removal of malic acid as carbon source. Research focus has recently shifted to
the ability of LAB and MLF as well as the interaction of LAB with yeast to alter the wine aroma
profile via the modification and/or production of certain aroma compounds.
The main goal of this study was to assess the impact of yeast and nutrient addition on the
ability of the NT 202 Co-Inoculant to conduct MLF during co-inoculation and to evaluate the
aroma compound production in the final wine.
The first aim was to evaluate the impact of different red and white wine yeast strains on the
ability of the NT 202 Co-Inoculant to conduct MLF during co-inoculation in Chardonnay, Merlot
and Shiraz. Malolactic fermentation was unsuccessful in the Chardonnay due to a low pH, but
successful in Merlot and Shiraz. Based on the malic acid degradation ability of the NT 202 Co-
Inoculant, the yeasts were grouped into three categories: inhibitory, neutral or stimulatory
towards MLF. Co-inoculated MLF showed a clear decrease in total fermentation time while
yeast strains such as WE 372 and Exotics showed positive compatibility with the NT 202 Co-
Inoculant. The impact of the yeast-bacterial combinations on the aroma compound production in
the final wine was evaluated. Co-inoculated MLF showed positive aroma changes in the red
wines with a general increase in total esters (associated with fruity characters in wine) especially ethyl lactate and diethyl succinate that also contribute to the mouthfeel of the wine.
Production of esters, volatile fatty acids and higher alcohols seemed to depend on the yeastand
LAB strain used. The NT 202 Co-Inoculant contributed to the monoterpenes produced and
MLF led to increased concentrations of diacetyl and acetoin, which are associated with buttery
characters in wine.
The second aim of this study was to evaluate the impact of wine additives (used during coinoculation)
such as yeast- and bacterial nutrients, clarifying- and detoxifying agents on the
ability of the NT 202 Co-Inoculant to conduct MLF and to assess their impact on the aroma
compound production in the final wine. No negative or positive impact on the malic acid
degradation of the NT 202 Co-Inoculant or the resulting aroma compound production was
observed for the different wine additives used in this study.
The results generated from this study showed that the selection of yeast strains is important
as it will influence both the fermentation duration and final wine aroma. === AFRIKAANSE OPSOMMING: Die invloed van appelmelksuurgisting (AMG) in die meeste rooi- en witwyne is een van baie
faktore wat wynkwaliteit beïnvloed, omrede dit die geur en sensoriese profiel van wyn
beïnvloed. Hierdie proses is 'n dekarboksileringsaksie wat deur melksuurbakterieë (MSB), soos
Oenococcus, Lactobacillus, Pediococcus en Leuconostoc, uitgevoer word. Die mees algemene
bakterieë wat gebruik word, is Oenococcus oeni, maar onlangs het Lactobacillus plantarum ook
na vore getree in die gebruik van kommersiële aanvangskulture. Die eerste gemengde AMGaanvangskultuur
(NT 202 Co-Inoculant) is in 2011 gekommersialiseer. Die rede vir die
oorheersende gebruik van O. oeni en L. plantarum word toegeskryf aan hul gehardhiedsgraad
in ‘n uitdagende wynomgewing.
Appelmelksuurgisting lei tot 'n afname in die suurheidsgraad en 'n toename in die pH van
die wyn, wat 'n sagter mondgevoel tot gevolg het. Nog 'n rede waarom AMG deurgevoer word,
is om die mikrobiese stabiliteit van die wyn te verbeter deur die verwydering van appelsuur as
koolstofbron. Die navorsingsfokus het onlangs verskuif na die vermoë van MSB en AMG, sowel
as die interaksie van MSB met die gis, om die wynaromaprofiel te verander deur middel van die
verandering en/of produksie van sekere aromaverbindings.
Die hoofdoel van hierdie studie was om die impak van die gis en voedingstof te evalueer
ten opsigte van die vermoë van die NT 202 Co-Inoculant om AMG uit te voer tydens
koïnokulasie. Die produksie van aromakomponente in die finale wyn is ook geëvalueer.
Die eerste doelwit was om die impak van verskillende rooi- en witwyngisrasse te evalueer
ten opsigte van die vermoë van die NT 202 Co-Inoculant om AMG uit te voer tydens
koïnokulasie in Chardonnay, Merlot en Shiraz. Appelmelksuurgisting was onsuksesvol in die
Chardonnay weens 'n lae pH, maar suksesvol in Merlot en Shiraz. In terme van die
appelsuurafbraakvermoë van die NT 202 Co-Inoculant, is die giste in drie kategorieë gegroepeer: inhiberend, neutraal of stimulerend teenoor AMG. Ge-koïnokuleerde AMG het 'n
duidelike afname in die totale fermentasietyd getoon, terwyl gisrasse, soos WE 372 en Exotics,
‘n positiewe verenigbaarheid met die NT 202 Co-Inoculant getoon het. Die impak van die gisbakteriële
kombinasies op die aromakomponentproduksie in die finale wyn is geëvalueer. Gekoïnokuleerde
AMG het positiewe aromaveranderinge in die rooiwyne getoon met 'n algemene
toename in die totale esters (wat geassosieer word met vrugtige karakters in wyn), veral
etiellaktaat en dietielsuksinaat, wat ook bydra tot die mondgevoel van die wyn. Dit het
voorgekom dat produksie van esters, vlugtige vetsure en hoër alkohole moontlik afhanklik kan
wees van die gis- en bakteriële ras gebruik. Die NT 202 Co-Inoculant het bygedra tot die
monoterpene wat geproduseer is en AMG het gelei tot verhoogde konsentrasies van diasetiel
en asetoïen, wat geassosieer word met botteragtige karakters in wyn.
Die tweede doelwit van hierdie studie was om die impak van wyntoevoegingsmiddels (wat
tydens koïnokulasie gebruik word) bv. gis- en bakteriese voedingstowwe, verhelderingsagente, asook detoksifiserende agente, te evalueer ten opsigte van die vermoë van die NT 202 Co-
Inoculant om AMG uit te voer en om hul impak op die produksie van die aromakomponente van
die finale wyn te ontleed. Geen negatiewe of positiewe effekte is waargeneem vir die
verskillende wyntoevoegingsmiddels, wat in hierdie studie gebruik is, in terme van die
appelsuurafbraak van die NT 202 Co-Inoculant of die gevolglike produksie van
aromakomponente nie.
Hierdie studie se resultate toon dat die keuse van die gisras belangrik is, omdat dit die
fermentasietydperk, asook die finale wynaroma, beïnvloed. === Anchor Yeast, Oenobrands, The National Research Foundation and THRIP, for financial support
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