Malolactic fermentation (MLF) is an integral step in red winemaking that results in a decrease in acidity and can also influence additional wine quality parameters. This study examined the impact of MLF on red wine color and the ability of Oenococcus oeni to degrade compounds important to the development of polymeric pigments. Pinot noir and Merlot wines were produced where a portion of the wines underwent a simultaneous alcoholic and malolactic fermentations with O. oeni strain VFO. Post-alcoholic MLFs were conducted using VFO and two additional O. oeni strains in sterile filtered wines. A control wine that did not undergo MLF was pH adjusted to the same pH as wines that had undergone MLF. Wines that underwent MLF (MLF+) contained lower concentrations of acetaldehyde and pyruvic acid than wines that did not undergo MLF (MLF-). Wines that underwent MLF with O. oeni VFO also had higher concentrations of caffeic and trans-p-coumaric acids. MLF+ wines had significantly lower color and polymeric pigment content than MLF-wines and contained significantly higher monomeric anthocyanins. Vitisin B concentrations were also significantly lower in wines that underwent MLF. These differences remained throughout nine months of storage, demonstrating that MLF can affect red wine color independent of pH change. While O. oeni influenced the concentration of phenolic and nonphenolic compounds involved in red wine color development there were no strain specific differences in color and polymeric pigment content.

Malolactic fermentation (MLF) is an important process in wine production due to the resulting reduction in acidity. MLF is typically induced by the addition of Oenococcus oeni after the completion of alcoholic fermentation (AF), but can occur concurrent with AF by co-inoculation of O. oeni with Saccharomyces cerevisiae. This study investigated the effect of MLF inoculation timing and temperature (15 °C and 21 °C) and the presence of the non-Saccharomyces yeast Torulaspora delbrueckii on Chardonnay wine aroma and mouthfeel. Aroma composition was measured using headspace solid-phase microextraction-gas chromatography mass spectrometry (HS-SPME-GCMS). Mouthfeel attributes of the wines produced were assessed by a winemaker panel, using Napping^® and Ultra-flash profiling. Significant differences in aroma composition and mouthfeel perception were found based on MLF timing and inoculation conditions, as well as between temperatures. Temperature had a greater impact on the aroma composition for sequential inoculations, while there were little differences based on the temperature of concurrent fermentations. Treatment type and temperature also affected the chemical composition of finished wines. Mouthfeel was impacted, although not as strongly as aroma composition. These findings demonstrate the usefulness of various MLF practices to influence the sensory qualities of a Chardonnay wine.

Yeasts isolated from a prefermentation cold maceration (at 8 to 9°C) of Vitis vinifera L. cv. Pinot noir grapes were evaluated for β-glucosidase activity. Among the 13 distinct yeast isolates investigated, five had β-glucosidase activity. Sequence analysis of the D1/D2 domain of the 26S rDNA gene confirmed the identity of these yeasts as Metschnikowia pulcherrima, Hanseniaspora uvarum, Lachancea thermotolerans, and two isolates of Saccharomyces cerevisiae. The β-glucosidase activity of these yeast isolates was further investigated at different sugar concentrations and temperatures before the isolates were used in the production of Pinot noir wines. Pinot noir grapes sterilized by high hydrostatic pressure were inoculated with the individual yeast species or a mixture of all yeast species. A seven day prefermentation cold maceration (9°C) was then performed, followed by alcoholic fermentation conducted by S. cerevisiae RC212 at 27°C. Pinot noir grapes were also cold-macerated without the addition of any yeast, while fermentations were also undertaken with no cold maceration. Solid-phase microextraction-gas chromatography-mass spectrometry analysis of the wines indicated that the presence of the different yeast species during the prefermentation cold-maceration altered the volatile aroma composition of the wines. These yeasts altered the concentrations of ethyl esters, branch-chained esters, higher alcohols, and some monoterpenes in the wines.