Winemaking From Koshu Variety by the sur lie Method: Behavior of Free Amino Acids and Proteolytic Activities in the Wine

Abstract

The involvement of proteolytic enzymes in the increase of amino acid concentrations for wines stored in contact with lees was investigated. The amino acid concentrations in the Koshu wine stored at 20°C were two-fold higher than those in the wine stored at 10°C during six months in contact with the lees. There was no increase in amino acid concentrations in the wines initially heated (60°C, 10 min). Although the intracellular protease and carboxypeptidase activities at pH 7 started to decrease from the onset of the sur lie treatment, their activities were still detected at the end of the six-month storage period. At pH 3, the protease activity in wines was very low throughout the storage period, and carboxypeptidase activity was not detected in the wines. In wines containing 100-fold higher volumes of lees at pH 3, the protease activity was clearly detected and it was stable during the two-month storage period tested. The addition of an acid-protease inhibitor, pepstatin, inhibited the increase of amino acids by 80% in the three months tested. The involvement of acid-proteases in the increase of amino acid concentrations in sur lie wines was clearly demonstrated, and the protease activity was derived from the yeast cells. The gradual increase of amino acids in wines during the sur lie was clearly shown to be due to stable protease with low activities which persisted in the wine.