Koshu is a pinkish-grey skinned table grape indigenous to Japan, that country’s best known variety. It is said to be a natural hybrid between an as-yet-unidentified variety of Vitis vinifera and an unknown hybrid whose parents are Vitis davidii x Vitis vinifera (research by Nami Goto, 2014). Legend has it that Koshu developed from grapes that travelled the Silk Road across Central Asia from the Caucasus to China and then to Japan, somewhere around 1,000 years ago.
The bunch: Clusters are long, the grapes are medium-sized.
Where grown: In Japan Koshu is mainly grown in Yamanashi Prefecture, a 90 minute train ride directly west of Tokyo, at the foot of Mount Fuji in the south-east of the province, and surrounded by mountains in the 3,000m (9,842ft) range. Around 480ha of Koshu are grown in Japan, 95% of which is in Yamanashi.
Yamanashi: Yamanashi Prefecture is the birthplace of winemaking in Japan. In 1874 the first wines were made there in Kufu city. In 1879 the first winery to enter into full scale wine production was in Iwaiamura, now Koshu City’s Katsunuma-cho. The Dainippon Wine Co Ltd, founded in 1877, had sent two young men to France. Their impetus led to the start of wine production in Japan using the Koshu grape. After World War Two, production increased dramatically. Climatic extremes of heat and cold, and long days of summer sunlight prevail here. The soils are of volcanic origin, well-drained, and fertile (peaches, cherries and grapes from here are renowned in Japan).
Disease-resistance: Koshu’s skins are said to be thick enough to withstand humid climatic conditions in Japanese summers.
Viticulture: The vine is robust and tree-like, difficult to plant in compact vineyards. Vines are this trained either to overhead pergolas (the Ichimonji-Tansho system) with spur pruning, or grow on VSP trellises, again with spur pruning (Cordon de Royat).
Wine style: Koshu wines are generally dry, pale straw in colour, delicately flavoured with notes of soft yuzu citrus, lychee, pear and peach.
Promotional body: The promotional body for Koshu is Koshu of Japan (KOJ). It was founded in 2015.
Yamanashi Prefecture Winemakers Association: This was founded to improve wine quality.
Oxford Companion to Wine 4th edition ed. Jancis Robinson MW and Julia Harding MW (Oxford University Press, 2015), p400-401.