| dc.description.abstract | Icewine is a sweet dessert wine fermented from the juice of grapes naturally
frozen on the vine. The production of Icewine faces many challenges such as
sluggish fermentation, which often yields wines with low ethanol, and an
accumulation of high concentration of volatile acidity, mainly in the form of acetic
acid. This project investigated three new yeast strains as novel starter cultures for
Icewine fermentation with particular emphasis on reducing acetic acid production: a
naturally occurring strain of S. bayanus/S. pastorianus isolated from Icewine grapes,
and two hybrids between S. cerevisiae and S. bayanus, AWRI 1571 and AWRI 1572.
These strains were evaluated for sugar consumption patterns and metabolic
production of ethanol, glycerol and acetic acid, and were compared to the
performance of a standard commercial wine yeast KI-VI116. The ITS rONA region
of the two A WRI crosses was also analyzed during fermentations to assess their
genomic stability. Icewine fermentations were performed in sterile filtered juice, in
the absence of indigenous microflora, and also in unfiltered juice in order to mirror
commercial wine making practices.
The hybrid A WRI 1572 was found to be a promising candidate as a novel starter
culture for Icewine production. I t produced 10.3 % v/v of ethanol in sterile Riesling
Icewine fermentations and 11.2 % v/v in the unfiltered ones within a reasonable
fermentation time (39 days). Its acetic acid production per gram sugar consumed was
approximately 30% lower in comparison with commercial wine yeast K I -V 1116
under both sterile filtered and unfiltered fermentations. The natural isolate S. bayanus/S. pastorianus and AWRI 1571 did not appear to be suitable for commercial
Icewine production. They reached the target ethanol concentration of approximately
10 % v/v in 39 day fermentations and also produced less acetic acid as a function of
both time and sugar consumed in sterile fermentations compared to KI-V1116.
However, in unfiltered fermentations, both of them failed to produce the target
concentration of ethanol and accumulated high concentration of acetic acid. Both
A WRI crosses displayed higher loss of or reduced copies in ITS rDNA region from
the S. bayanus parent compared to the S. cerevisiae parent; however, these genomic
losses could not be related to the metabolic profile. | en_US |
