Everything you need to know about Koshu from Japan

Where is it grown?

Koshu’s primary growing area is Yamanashi, which is a basin-shaped viticultural region, with vines on the lower slopes of the surrounding mountains. Landlocked, the area is protected from the Pacific ocean’s prevailing winds, rainfall, and typhoons by the perfectly cone-shaped, snow-capped, volcanic wonder that is Mount Fuji – the most powerful visual symbol of Japan.

Nevertheless, this is a wet, humid region. While Yamanashi’s vineyards like on the 35^th Parallel North, which runs through California, southern Spain and Italy, this part of Japan differs from these wine regions due to the incidence of summer rainfall, with around 80% of the 800-1000mm of precipitation of Yamanashi falling during the growing season. Furthermore, Yamanashi’s viticutlural heartland, Katsanuma, is one of the warmest places in Japan. Combine the heat, and summertime rainfall, and Yamanashi is more like Australia’s New South Wales, particularly Hunter Valley, than it is somewhere like Sonoma.

Koshu, however, thrives in Yamanashi, not due to its rot-resistant skins, but also due to its natural adaption to the fertile clay soils of the area, which, importantly, overlay a free-draining volcanic base, preventing waterlogging.

How is it grown?

In keeping with Japan’s reputation for precision in technology, the country’s viticulturists go to extraordinary lengths to protect the Koshu grapes, choosing to train them high in pergolas, improving airflow around the bunches, while also shading the grapes from temperature extremes.

They also protect the Koshu grapes from summer rainfall with little wax paper hats stapled together above each bunch, ensuring that the water doesn’t get inside the bunches. Otherwise, the water might start the spread of rot, which would spread rapidly in this warm and damp climate.

It’s an effective, if quite expensive technique, not used anywhere else in the world. As for the rainfall that does wash onto the ground, the free-draining soils of the Yamanashi area, many of them volcanic in origin, ensure that the berries themselves don’t swell too much, preventing the resulting wines from suffering from dilution.