Impact of fermentation technology on the phenolic and volatile composition of German red wines

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Abstract
Summary: Homogenous grape material of the red varieties c.v. Pinot noir, c.v. Dornfelder and c.v. Portugieser were fermented on an industrial scale using a special fermenter for pump over and punch down treatment. On pilot scale, thermovinfication was carried out at 60 °C and a manual punch down treatment was used in open containers. Both the mechanical punch down and pump over treatment significantly enhanced the extraction of all phenolic compounds and their polymerization in comparison to the traditional manual punch down treatment. Applying an excess of mechanical maceration increased the extraction of seed and stem phenols, but slowed down their polymerization. Assessing volatile composition, the biggest differences occurred between wines made by thermovinification versus those fermented on their skins. Slow fermentation kinetics and low solid content in the juice enhanced ester formation in thermovinied wines. Thermal inactivation of lipoxygenase enzyme systems reduced C6‐alcohols and their subsequent esters in thermovinified wines. Only small differences occurred between punch down and pump over tanks except that the pump over regime gave all varieties of wines significantly higher quercetin levels. In conclusion, the application of modern fermentation equipment seemed to be more relevant to improve extraction and polymerization of phenolic compounds, while thermovinification yielded wines with high ester content giving a more fruity style.