Sensory and Color Changes Induced by Microoxygenation Treatments of Pinot noir before and after Malolactic Fermentation

Different microoxygenation procedures before and after malolactic fermentation were applied to Pinot noir wines from two consecutive vintages using the same Pinot noir block and a standardized winemaking protocol. The effects of microoxygenation treatments were investigated by spectrophotometry, HPLC-DAD, and descriptive sensory analysis. Microoxygenation before malolactic fermentation was carried out in 250-L red wine fermentors at oxygen dosages of 20 and 100 mg/L/month for 20 days. Oxygen dosages of 1 and 5 mg/L/month were applied for three months after malolactic fermentation using 100-L stainless-steel tanks. CIELab results showed that microoxygenation in 2006 tended to yield light-colored wines with an increase in yellow tonality. Examining monomeric polyphenols after alcoholic fermentation, this oxygen-induced color loss may be related to the high flavan-3-ol to anthocyanin ratio in this vintage. Furthermore, twice the increase in acetaldehyde content upon microoxygenation after malolactic fermentation was observed in 2006, which indicated excess oxygen for these wines. By contrast, a low flavan-3-ol to anthocyanin ratio was determined after alcoholic fermentation in wines of vintage 2007. Predominantly, these wines showed an increase in blueness upon microoxygenation treatments. Low correlations among astringency related attributes proved that the chosen attributes independently characterized the sensory variation in tannic structure among the microoxygenated Pinot noir wines. Descriptive analysis revealed that microoxygenation predominantly diminished green tannins in 2006 wines. Dry tannins, although decreasing in course of microoxygenation with low oxygen doses, rose again at higher oxygen doses. Beneficial aroma changes in 2006 and the increase of color intensity in 2007 were more salient upon microoxygenation prior to malolactic fermentation. An unfavorable impact on Pinot noir aroma occurred primarily due to microoxygenation after malolactic fermentation.