Microwave maceration for control of laccase and enhanced phenolic outcomes in Shiraz wine

Microwave maceration is a novel process for red winemaking with several potential benefits. During 2013 vintage, microwave maceration was applied to Shiraz grape must from the Hunter Valley and demonstrated to be effective for eliminating laccase from juice, and for rapid extraction of phenolic compounds for winemaking. In some years, Botrytis heavily impacts Hunter Valley Shiraz. Microwave maceration was applied to musts made from 12 Botrytis-affected bunches of Shiraz, with infection levels ranging between 1% and 40%. Mean laccase concentration was 8.2 µg/mL before maceration and 0.9 µg/mL after. To compare wine phenolic outcomes from microwave maceration of Shiraz, replicates of 200gm of must were microwave macerated and pressed-off prior to inoculation for alcoholic fermentation. Control wine was made from 200gm replicates of Shiraz must fermented on pomace. Two hold times were trialled for the microwave macerated must (short and long) and wine phenolics were assessed by UV-visible spectrophotometry. The long hold time wine was phenolically equivalent to control wine for mean concentration of: total phenolics, total pigment, free anthocyanin, total tannin, pigmented tannin and colour density. Short hold time wine was significantly lower than control wine for mean concentration of: total pigment, free anthocyanin and colour density, but equivalent for: total phenolics, total tannin and pigmented tannin. The findings reported here are based on a single small-scale trial, although microwave maceration has been extensively tested at laboratory scale on Pinot noir. The opportunity to eliminate laccase and better manage phenolic outcomes in Shiraz wine could be of benefit to industry. The research team is looking to pilot microwave maceration of Shiraz with industry in 2014.