Impact of malolactic fermentation on red wine color and color stability

Graduation date: 2012Malolactic fermentation (MLF) is an important step in the production of wines and is commonly performed in red or cool climate wines to reduce acidity. In this study the impact of MLF on red wine color and the ability of Oenococcus oeni to degrade compounds important to the development of stable color were studied. Pinot noir and Merlot wines were produced, where simultaneous alcoholic and malolactic fermentations were induced in half of the wines. At dryness, all wines were pressed prior to sterile-filtration through 0.45 μm membranes. Wines that had not undergone malolactic fermentation (MLF (-)) were then either (a) inoculated with one of three strains of O. oeni (MLF (+)) or (b) pH adjusted to the same pH as MLF (+) wines. All wines were sterile-filtered, bottled, and stored at 13°C for analyses. MLF (+) wines had lower concentrations of acetaldehyde, pyruvic acid, and caftaric acid than MLF (–) wines. MLF (+) wines had significantly\ud lower color and polymeric pigments than MLF (–) wines while containing significantly higher monomeric anthocyanins. These differences were consistent throughout 12 months of storage demonstrating that MLF can affect red wine color independent of pH change and that O. oeni can impact phenolic and non-phenolic compounds involved in red wine color development.\ud Wine produced in a subsequent year was used to investigate possible reasons for the color loss caused by MLF as well as practical strategies to minimize these losses. One such strategy was to delay MLF, a practice that winemakers believe results in greater red wine color. Wines were held at 13°C for 0, 14, 28, 100, and 200 days before inoculation with O. oeni VFO to induce MLF at 25°C. Delaying MLF did not impact loss of color @ 520nm as all wines still experienced a color loss. However, as MLF was delayed for increasing time periods the polymeric pigment content and monomeric anthocyanin concentration of MLF (+) wines became more similar to those of the control. After 200 days delayed MLF, there was no statistically significant difference between the MLF (+) and control wine for polymeric pigment and only a minor difference in concentration of monomeric anthocyanins.\ud The reduced loss of polymeric pigment in delayed MLF wines may have been due to acetaldehyde being in the wine for a longer period of time as demonstrated in experiments investigating the impact of O. oeni metabolism of acetaldehyde and pyruvic acid metabolism. Wines that had undergone MLF were supplemented with\ud acetaldehyde and pyruvic acid to the levels measured in MLF (–) wines. Wines with acetaldehyde or acetaldehyde and pyruvic acid additions showed higher color and polymeric pigment than MLF (+) wine with no additions while addition of only pyruvic acid addition showed no improvement in color or polymeric pigment in comparison to standard MLF (+). However, acetaldehyde additions did not completely prevent a loss of color at 520nm after MLF. Whether this color loss was due to fining by O. oeni was investigated through exposure of wine to live or inactivated O. oeni for differing time periods. Wines that did not undergo MLF but were exposed to live or inactivated cells showed no difference in color, polymeric pigment, and monomeric anthocyanin compared to the control suggesting that loss of color during MLF was not due to fining by O. oeni cell