Wild Japanese fruit used in new wine grape variety

Researchers led by Professor Emeritus Takuji Hoshino of Okayama University of Science (OUS) have developed a new wine grape variety named ‘Muscat Shiragai’, created by crossing the wild-species Shiraga grape with Muscat of Alexandria.

The hybrid grape has been officially approved for registration as a new variety by Japan’s Ministry of Agriculture, Forestry and Fisheries (MAFF).

The Shiraga grape, native only to the Takahashi River basin in Okayama Prefecture, is known for its high sugar content, low acidity, resistance to fruit cracking, and tolerance to black rot and ripe rot. First described as a new species in 1918 by botanist Tomitaro Makino, its Japanese name derives from Jukichi Shiraga, the botanist who discovered it.

“I wanted to create a wine grape that incorporates wild genetic traits,” Hoshino said. “If this grape becomes widely cultivated and its wine contributes to regional revitalisation and tourism, that would be the best outcome.”

Hoshino, who specialises in plant systematics, became the founding director of the Institute of Viticulture and Enology at OUS in 2017. While collaborating with representatives of Funao Winery in Kurashiki City, he turned his attention to the Shiraga grape, which is rare and endangered and found only in limited areas of Okayama Prefecture. This inspired the idea of creating a uniquely ‘Okayama-born’ wine grape by hybridising it with Muscat of Alexandria.

In February 2018, OUS signed a comprehensive cooperation agreement with Kurashiki City and Funao Winery, launching the project as part of a national government-recognised regional revitalisation initiative to promote ‘branding of local resources’.

By fiscal year 2022, wines were being brewed from different breeding lines and evaluated for sugar content, acidity, pH and taste, leading to the selection of promising strains. Drawing on these trial results, the Muscat Shiragai variety was finalised in 2024. The official application for new variety registration was jointly filed by Kake Educational Institution and Kurashiki City in December 2024 and was publicly announced in June 2025. Official registration is expected within four to five years.

A press conference held at OUS to launch the new wine grape variety was attended by Kurashiki Deputy Mayor Kenji Komatsu, Funao Winery CEO Kenichiro Miyake and OUS President Hiroyuki Hirano. Participants who sampled the Muscat Shiragai grapes and wine described the fruit as “sweet and very delicious”, and the wine as having “a subtle Muscat aroma and smooth drinking quality”.

“We are very much looking forward to offering a wine filled with the unique charm that can only be produced in Kurashiki. We also anticipate further research results to refine Muscat Shiragai into an even more sophisticated grape,” Komatsu said.

Hirano added: “Collaboration among industry, academia and government is essential for building innovative local communities. OUS will continue integrating education and research, returning the results to the community, and contributing to solving regional and social issues.”

Currently, 20 vines are cultivated at Funao Winery and the OUS vineyard, yielding 41.6 kg in 2024. An additional 300 grafted vines were planted at the end of fiscal year 2023, with a goal of harvesting more than 500 kg by 2028–2029.

The team also plans to optimise practices such as leaf removal, fertilisation and irrigation to further improve quality.

Image caption: The fruit and wine of the newly developed  Muscat Shiragai grape, presented at a press conference by Professor Emeritus Takuji Hoshino (right). Pictured on the left are Kurashiki Deputy Mayor Kenji Komatsu, OUS President Hiroyuki Hirano and Funao Winery CEO Kenichiro Miyake. Image credit: Okayama University of Science.