|Abstract or Summary
- The purposeful induction of malolactic fermentation (MLF) in wines such as Pinot Noir
and Chardonnay is an established commercial wine making practice in Oregon. This induction
is not always successful, especially with white wines, such as Chardonnay. A study was
initiated to examine the compatibility of yeasts commonly used in Oregon winemaking with
various strains of malolactic bacteria.
In preliminary and pilot plant scale experiments, the yeast strain found to be most
conducive to malolactic fermentation by lactic acid bacteria was Montrachet (Red Star). The
malolactic bacterial strains that were best able to complete malolactic fermentation in various
wines, fermented by different yeast strains, were the two Oregon commercial strains, ER1A
and Ey2d, and the Pinot Noir juice isolate, DAPN85A.
Sensory analysis of aroma by difference from control test was done on Chardonnay
wine fermented by 4 different yeast strains and 3 different malolactic bacterial strains. In all
cases, there was an overall significant difference in malolactic fermented wine aroma when
compared to control wines.
Organic acid analyses by high pressure liquid chromatography (HPLC) and analyses of
volatile compounds by gas chromatography (GC) and gas chromatography-mass spectrometry
(GC-MS) were done on selected Chardonnay wines. Propionic acid was found to diminish in
malolactic fermented wines while acetic acid content increased. Isobutanol and isobutyraldehyde increased significantly in MLF wines, compared to the controls. Chemical
analyses of MLF and control wines suggested two possible chemical reactions resulting from
the MLF. The first was the reduction of isobutyraldehyde to isobutanol, and the second was
the hydrolysis of isobutyl acetate to isobutyraldehyde and acetate. On all GC chromatograms of
wines, where MLF had occurred, there was an unidentified peak close to the retention time of
isoamyl acetate. This peak was not evident in wines where MLF had not occurred.
Eight compounds were tentatively identified by GC-MS in malolactic fermented wines
which were not found in the control wines. These were 4-methyl-3-pentanoic acid, methyl
acetate, ethyl hexanoate, hexyl acetate, 1,12-tridecadiene, hexadecanoic acid, and a
compound which was tentatively identified as farnesol, or 1,2-benzenedicarboxylic acid. The
latter four compounds had identity fits of less than 900 from the mass spectral analysis.
Whether any of these eight compounds match the unknown "ML peak" found in the GC
chromatograms is unknown.