Impact of malolactic fermentation on red wine color
The color of a red wine is an important sensory attribute that originates primarily from anthocyanins. However, development of stable red wine color is impacted by compounds such as p-coumaric acid, caffeic acid, catechin, and quercetin that are involved in copigmentation reactions as well as acetaldehyde and pyruvic acid. While it is known that yeast can alter the concentrations of some of these compounds, little is known regarding the impact malolactic bacteria may have on red wine color development. This project is investigating the effect of the malolactic fermentation (MLF) on red wine color and the ability of malolactic bacteria to degrade compounds important to the development of stable red wine color.
Pinot noir and Merlot wines were produced using grapes from the Oregon State University vineyard and were fermented with Saccharomyces cerevisiae VQ15. Concurrently, a third of Pinot noir musts were inoculated with Oenococcus oeni. At dryness, wines were pressed and filtered (0.45 µm nominal) with a second third of the wines being inoculated with O. oeni VFO (remaining third was was not inoculated). Some of the wine that had not undergone MLF was pH adjusted to the same final pH of wines that had completed MLF. Samples were taken before and after MLF for analysis and wines were sterile filtered, bottled, and stored at 55° F.
Prior to MLF, all Pinot noir wines had very similar concentrations of acetaldehyde and pyruvic acid. This was also the case with the Merlot wines. However, all wines that had undergone MLF, including the simultaneously fermented Pinot noir wine, had lower acetaldehyde and pyruvic acid concentrations. Pinot noir wines that had undergone MLF also had lower wine color and polymeric pigment values compared to wines that had not gone through MLF. For the Merlot wines, wines that had undergone MLF also had lower wine color, copigmentation, anthocyanins, and polymeric pigment than wines that had not undergone MLF with the differences being more pronounced then what was observed for the Pinot noir wines. The phenolic composition of wines that underwent MLF was different from wines that had not. Both Pinot noir and Merlot wines that had undergone MLF had lower levels of caftaric acid and higher levels of caffeic acid than wines that had not undergone MLF. Wines that did not undergo MLF also had lower malvidin glucoside and monomeric anthocyanin concentrations than wines that had undergone MLF. Finally, the concentration of tannin in Pinot noir wines that had undergone MLF was lower than in wines that had not. These results demonstrate that MLF as well as time of bacterial inoculation can effect the concentration of phenolic and non-phenolic compounds involved in red wine color development.
