Daiki Kiyomichi, Hideki Takase, Kanako Sasaki, Gen Ikoma, Hironori Kobayashi, and Ryoji Takata*
*Kirin Holdings, Company, Limited, 26-1 Muraoka-Higashi 2-Chome, Fujisawa, Kanagawa, Shonan Health Innovation Park 12-12, 251-8555, Japan (ryoji_takata@kirin.co.jp)

Koshu is an indigenous grape variety that has been grown in Japan for over a thousand years. Recent research showed that it has 70% Vitis vinifera genes. It is the most-cultivated variety for winemaking in Japan.

The variety is mainly used to produce white wines, including a skin-contact fermented white wine which is fermented with seeds and skin. There little known about the extraction of phenol compounds during fermentation and maceration of Koshu wine. Thus, the objective of this study is to reveal the character of skin-contact fermented white wine by examining its phenolic compounds.

In this study, Koshu was compared with other V. vinifera varieties, Sauvignon blanc (SB) and Merlot (MN). Fruit tissues were separeted into pulp, seed, and skin and soaked separately in model wine solution (12% ethanol, 3000 mg/L tartaric acid, pH 3.2) for 14 days to determine extraction of phenolic compounds. The results showed that proanthocyanidin was extracted from SB and MN seeds and its content increased during soaking. Proanthocyanidin was not extracted from Koshu seeds, despite the presence of proanthocyanidin. The three varieties were fermented with seeds and skin during 28 days to study the behavior of extraction of phenolic compounds during fermentation and maceration. The results showed that the content of proanthocyanidin in Koshu wine decreased dramatically during maceration. In contrast, that of SB and MN wine was stable or increased during maceration.

These new findings on the unique characteristics of proanthocyanidin in Koshu grape show the diversity of character in Vitis and contribute to the control of wine taste.

Funding Support: Kirin Holdings, Company, Limited