Heat moved the calendar. Night-and-day range kept the fruit honest.
YBS News (NNN) reports crush starting on 24 August at Château Mercian Katsunuma Winery in Kami-Iwasaki, Katsunuma-cho, Koshu. After a rite for safety and quality, the team pressed about 1,500 kilograms of Koshu. Heat advanced ripening by about a week. Diurnal range — warm days, cooler nights — still kept quality solid. Crush runs through mid-October.
Koshu is Japan’s pale, pink-skinned white grape, often grown on overhead pergolas in Yamanashi’s Kofu basin. An early start does not end the season. The winery will keep taking fruit for weeks, so one hot August week is not the whole vintage.
General manager Kobayashi Hironori says the house is expanding higher-elevation plantings and heat-tolerant varieties. Higher ground is a climate tool: nights stay cooler, and sugar races less. Yamanashi, he argues, must lead Japan’s wine industry, with growers, government and schools thinking together.
Mini-concept: diurnal range is the night–day temperature gap. Heat can rush sugar. Cool nights can hold aroma and freshness, so an early crush is not automatically a thin wine.
A canned drink never waited on a mountain night. Koshu from these pergolas does.
Hold the pattern: one week early still needs cool nights to stay Koshu.