- Many different strains of yeast have been isolated from the natural
microflora on fruits. It has been known for some time that these
strains of yeast have distinct fermentation characteristics and, when
used in the production of wine, impart these characteristics to the
wine. These characteristics may be evidenced in the flavor or aroma
of the wine, the speed of the fermentation, the amount of ethanol
produced and many other ways.
It was reasoned that these fermentation characteristics were involved
with or were a result of the metabolic system of a particular
yeast strain. Since fermentation products result from the metabolic
pathways, these products were studied in the hope that a better understanding
of the fermentation products would lead to a better understanding
of the metabolic pathways and, in turn, of the fermentation
characteristics of yeast strains.
The fermentations were conducted on blackberries with four strains of yeast, chosen because of their different fermentation characteristics: Saccharomyces oviformis, Saccharomyces bayanus, Saccharomyces
ellipsoideus and Saccharomyces cerevisiae.
Ethyl chloride was used to extract the wines after the fermentations
were completed. The solvent was removed and the sample
concentrated on a low temperature distillation apparatus, after which
it was analyzed using gas chromatography. The gas chromatograph
employed was a Wilken's Aerograph Hy-Fi with a hydrogen flame
ionization detector. An eight foot X 1/8 inch stainless steel column
packed with five percent Carbowax 400 on 80/100 mesh Celite 545
was used for the analyses.
Peak heights were determined by measuring the recorder response
(in millivolts), and the percent contribution of each peak was
calculated with the greatest percent deviation within a sample being
less than four percent.
The initial five peaks, excluding ethanol and the solvent, accounted
for approximately 99 percent of the sample and demonstrated
significant differences between the yeast strains. The later peaks
also aided in the differentiation although not in as pronounced a manner.
A tentative identification was made, using the enrichment technique,
of peaks two, three, four, five, six, seven, nine, ten, thirteen
and fourteen. These were believed to be ethyl acetate, ethanol, propanol, isobutanol, butanol, isoamyl alcohol and active amyl alcohol,
glycerol, 2, 3-butylene glycol or ethyl octanoate, linalool and