CHARACTERISTIC EXTRACTION OF THE PHENOL COMPOUNDS IN KOSHU (VITIS VINIFERA CV.) WINE DURING THE MACERATION

Abstract

Koshu is one of the indigenous grape variety that has been grown in Japan for more than one thousand years. Recent research showed that it has 70% of Vitis vinifera genes. In 2010, the Koshu variety was included in ‘International List of Vine and Varieties and their Synonyms’ managed by the ‘International Organisation of Vine and Wine’ and has further fueled its popularity in Japan. It is the most cultivated variety for winemaking in Japan.
Koshu berries have light purple skins. The variety is mainly used to produce white wines such as an aromatic wine and a wine produced by sur lie method although various styles are produced. Whereas it is also used to produce orange wine which is fermented with their seed and skin. Previous study showed that β-damascenone could contribute to the fruity aroma in this style of wine. However, there is a few knowledge about the behavior of extraction of the phenol compounds during the fermentation and maceration, even though they are important compounds for the taste balance of such style. Furthermore, wines produced by Koshu grapes are sometimes described as bitter. Thus, the object of this study is to reveal the character of Koshu wine which is produced by the maceration at the point of view of phenol compounds.
In this study, Koshu was compared with other V. vinifera varieties, Sauvignon blanc (SB) and Merlot (MN). Each fruit tissues were separeted in pulp, seed and skin, and soaked separately in model wine solution (12% ethanol, tartaric acid 3000 mg/L, pH 3.2) during 14 days for study its capacity of extraction of phenol compounds at same alcohols degrees as wine. The results showed that proanthocyanidin was extracted by SB and MN seed and its content incresase during the sorking. On the other hand, proanthocyanidin was not extracted by Koshu seed, despite the presence of proanthocyanidin. Furthermore, these 3 varieties were fermented with seed and skin during 28 days for study the behavior of extraction of the phenol compounds during the fermentation and maceration in Koshu wine. The result showed that the content of proanthocyanidin and total phenols in Koshu wine were dramatically decreased during maceration. In contrast, those of SB and MN wine were stable or increased during maceration.
These new findings on the unique characteristics of proanthocyanidin in Koshu grape could might be showed the diversity of character in Vitis. And these insights are expected to contribute to the control of the taste of wine.