English

Seishu, more generally known as Sake, is a traditional Japanese alcoholic beverage. It is a fermented product from rice, just as Beer from barley or Wine from grapes. Quite different from either Beer, which is brewed with multiple sequential fermentations, or Wine, which is brewed with simple fermentation, Sake is brewed with multiple parallel fermentations. The multiple parallel fermentations for Sake brewing involve two microorganisms, the mold Aspergillus oryzae and the yeast Saccharomyces cerevisiae. Basically, the former digests and converts starch to glucose and the latter, glucose to ethyl alcohol and carbon dioxide. These two different reactions proceed simultaneously through most of the fermentation period in the same container, requiring highly sophisticated control techniques.

Common to the making of Sake, Beer, and Wine, as well as most other alcoholic beverages of the world, the yeast plays the most important role as it converts sugar to alcohol.

In 2013, we isolated a yeast from a flower called Fuyou (Cotton rosemallow, Confederate rose, or Dixie rosemallow, Hibiscus mutabilis), and in collaboration with the Food Research Center of Aichi Center for Industry and Science Technology (Nagoya) we have found that the yeast, named Hm-1, possesses excellent alcoholic fermentation capacity with potentials of producing elegant aromas and tastes. Incidentally, the flower Fuyou denotes “a graceful lover and delicate beautyrdquo; in the Japanese cultural tradition.

In 2016, we began to use the yeast Hm-1 to brew Sake from 200 kg of total rice at Toshun Shuzo Co., Ltd. (Nagoya), together with the Food Research Center. The year 2018 marked the 3^rd fermentation for the production of Sake, which we have named “Hakua.” The name Hakua signifies the beautiful chalky-white campus of Chubu University, as it is lyrically described in the school song of the University. The label for the bottle bears 白亞(Hakua) written by the calligrapher Lecturer Tokoku Harada of the University. We are now producing 500 to 1200 bottles of 720 mL yearly, which are commercially available from Chubu University Services Co., Ltd.

We have been working on this program since 2013, and technically have nearly finished sequencing the genome of the yeast Hm-1, of which we hope to make good use, for instance, to evaluate potentials of the yeast and to generate better strains by classical genetic manipulation. We have firmly determined to continue improving the quality of the Chubu University Sake brand. And may we wish, consequently, to see that our yeast Hm-1 should produce Sake with aromas of “a graceful lover” and with a taste of “delicate beauty.”

In 2013, “Washoku,” the traditional dietary culture of the Japanese, was added to UNESCO’s Intangible Cultural Heritage. According to the Foreign Ministry of Japan, the number of Japanese restaurants in the world more than doubled from 55,000 in 2013 to 118,000 in 2017, supposedly toppling either the Chinese or French cohorts. Along with this trend, which we could call the Japanese cuisine boom, Koshu Wine, a white wine produced from a Japanese grape named Koshu, has drawn attention as the best choice to accompany all kinds of Japanese cuisine ranging from Sushi, Tempura, Rahmen, and Takoyaki to simple-yet-elaborate and superbly elegant sets of dinners exemplified by the likes of Kaiseki Ryori and Shojin Ryori.

The French-led OIV (Organisation Internationale de la vigne et du vin, in French, and the International Organisation of Vine and Wine, in English) defines a full-fledged wine as the one made only from the Vitis vinifera grapes that have their roots in the Caucasus region.

Therefore, in 2004, one of our collaborators, Millesime, asked the US official agent Foundation Plant Services in University of California in Davis to classify Koshu according to its genome-based analysis. They identified Koshu as being largely V. vinifera, possibly with some traits of a Continental East Asian Vitis species, providing solid genetic evidence to support the old local legend that by the year 718, Koshu had reached the Japanese islands from over the Sea of Japan having traveled from far and away via the Silk Road. In 2010, the OIV approved the inclusion of the Koshu grape in the list of wine-making grapes. In 2015, groups of the National Research Institute of Brewing (NRIB, Japan) and Dalhousie University, Nova Scotia, collaborated to improve the identification data, which proposed that Koshu is a hybrid of 71.5% V. vinifera and 28.5% V. davidii, an East Asian species.

Koshu has long been recognized as a table grape to be eaten as it is. Historically, wine was produced from damaged or leftover unsold Koshu grapes. Accordingly, the quality of such wine was low and unappreciated. Around the turn of the century from the 20th to the 21st century, a small group of people interested in wine-making had decided to depart from such old practices and to drastically change their ways of making Koshu wine, first by introducing novel ways of growing Koshu grapes and second by introducing new methods of making wines.

Koshu is known to produce grapes of very low sugar content, averaging only Brix 15 to 16%. With only this amount of sugar, we cannot make wine having an alcoholic content any higher than about 9%. A few growers tried to grow Koshu by using a training system called vertical shoot positioning (VSP: Kakine-jitate), which would likely produce grapes with a higher sugar content than had been achieved by the traditional Japanese pergola system (Tana-jitate); but they had only marginal success.

The VSP result, therefore, forced us to attempt to improve biogenetically the present Koshu cultivar to produce grapes with higher sugar content. Most, if not all, of presently available Koshu cultivars are infected with many viruses, among which the leafroll viruses are well acknowledged to cause the suppression of sugar levels in grapes. Thus, one apparent way to enhance the sugar level of Koshu is to eliminate viruses. The viral elimination can be achieved by meristem-cultivation.

Based on these facts and the realization of the first importance that Koshu should be free of viruses, we have so far established a robust method of viral detection and an innovative way of meristem-cultivation to create novel cultivars free of viruses. The virus-free cultivars we produced have so far proven to bear grapes having a sugar content of no less than 20% Brix when grown in a green-house environment. As compared with their parental Koshu grapes, those grapes made wine, which possesses not only a more gentle and elegant flavor (nose), but also a smoother and more velvety taste with a longer and more refreshing finish. Our present aim is to develop more efficient methods of producing meristem-derived cultivars and to produce wine from virus-free Koshu grapes grown in large agricultural fields.