Photo/Illutration Bottles of wine from Koshu grapes harvested in 2020 are shown in October in Koshu, Yamanashi Prefecture, home to many wineries. (Jin Naganuma)

The Koshu white wine grape, a long-time specialty of Yamanashi Prefecture, has the rare distinction of containing genetic characteristics typical of red wine grapes, according to researchers.

Scientists from the University of Yamanashi and Tokyo University of Agriculture carried out the genome analysis of the species indigenous to Japan largely because genomic studies of wine grapes have been conducted widely overseas.

The first part of the study, led by Keisuke Tanaka, an assistant professor of genome biology at Tokyo University of Agriculture’s Genome Research Center, found the Koshu grape has genetic features that generate a citrus-like aroma and polyphenol, a substance found in large amounts in red wine grapes.

That indicates the Koshu grape is closer to a red wine grape than a white one.

Shinichi Enoki, a biological assistant professor at the Institute of Enology and Viticulture of the University of Yamanashi, then compared the genetic data of the grape with 130 kinds of red and white grapes from Europe and elsewhere.

Koshu does not belong to any species currently cultured in Europe or the United States, and no similar grape variants have been discovered in the world, according to the scientists.

Koshu grape wine is known by some experts in Yamanashi Prefecture for its astringency, a feature typically connected to red wine. The latest research backs this insight, and it could be used to improve wine quality and promote sales overseas.

“Taking advantage of the genetic information will help increase the efficiency of breeding for further quality improvement,” Enoki said. “That may render various processes easier, such as raising the aroma and sugar level and adjusting the strength of astringency.”

The grayish pink grape has been used to make white wine in Yamanashi Prefecture since the Meiji Era (1868-1912). It was registered as a wine grape by the Paris-based International Organization of Vine and Wine in 2010.

The species is mainly grown in Koshu, Yamanashi Prefecture.

Of the 3,416 tons of Koshu grapes produced in Japan in fiscal 2018, 96 percent came from Yamanashi Prefecture.

Typical beverages from Koshu wine grapes are slightly tart with flavors of citrus fruits and pears.

In 2013, the National Research Institute of Brewing in Hiroshima Prefecture found through a DNA analysis that Koshu emerged through the crossbreeding of a European wine grape and a wild variant native to East Asia.

Mitsuhiro Anzo, chairman of the Yamanashi Prefecture Wine Manufacturers’ Association and general manager of beverage maker Mercian Corp., said he had heard from a senior official that the Koshu species “may revert to a red wine grape.”

“I can now understand the reason for that,” Anzo said.

Koshu wine has recently been commended in international competitions, and its exports are rising.

“I want to strongly emphasize the individuality and uniqueness of Koshu wine,” Anzo said.

As to the origin of the Koshu grape, one local theory posits that Gyoki (668-749), a Buddhist priest in the Nara Period (710-784), dreamt of Bhaisajyaguru eating grapes, and founded Daizenji temple in what is now Koshu’s Katsunumacho district to form a grape farm.

Another theory is that a resident of present-day Katsunumacho identified a different grape species from the wild crimson glory vine, and planted it at home during the latter half of the Heian Period (794-1185).

The researchers’ findings were published in the international science journal Frontiers in Plant Science in early November.

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