Grape Guide
Koshu
RoséKoshu is Japan's flagship wine grape, a pink-skinned variety grown overwhelmingly in Yamanashi prefecture west of Tokyo. It yields pale, low-aroma, citrus-edged whites of light body and modest alcohol, now made in styles from lees-aged dry to sparkling and skin-contact.
Key Characteristics
- Genetic hybrid: roughly 70% Vitis vinifera with East Asian wild-vine ancestry
- Pink, thick-skinned berries with a vigorous, late-ripening vine
- Traditionally trained on overhead pergolas to cope with humid summers
- Resists botrytis well but is prone to downy and powdery mildew
- Recognised by the OIV in 2010, allowing its name on EU-bound labels
Typical Flavors
Major Regions
Yamanashi (Katsunuma, Kofu Basin) · Yamanashi (Hokuto, Akeno) · Nagano · Yamagata · Shimane · Osaka · Tottori
Overview
Koshu makes some of the most restrained white wines in commercial production. The pink-skinned berries give modest colour and phenolic extraction, and the aromatic signature is quiet: citrus rind, pear and a stony, faintly saline finish rather than overt fruit. Alcohol is usually moderate, commonly in the range of 10.5 to 12.5 percent, and the wines are built for freshness and delicacy rather than weight. The grape is closely tied to Yamanashi prefecture, which accounts for the great majority of Japanese plantings, and to the cuisine of the country, where its neutrality suits raw fish, tempura and dashi-based dishes. Winemakers add interest through extended lees contact, barrel fermentation, tank-method and bottle-fermented sparkling, and prolonged skin maceration that produces amber-orange wines. Most examples are intended for early drinking, although the richer lees-aged and barrel-fermented cuvées can hold for several years.
Origins & History
Koshu has been grown in Japan for centuries, and local tradition places its discovery at Katsunuma in Yamanashi in the late twelfth century, or its introduction from China by Buddhist monks along the Silk Road. Neither account is documented, and the variety's true origin remained unclear for a long time because Vitis vinifera is not native to East Asia. Genetic work has since shown that Koshu is not a pure vinifera. A 2015 study using ancestry-informative SNP markers placed it at about 70 percent Vitis vinifera and about 30 percent wild East Asian Vitis, and partial chloroplast sequencing suggested that the maternal line probably comes from the Chinese species Vitis davidii or a close relative. The most plausible reading is that a vinifera vine arriving from Eurasia hybridised with a wild vine in East Asia long ago. Earlier microsatellite work found Koshu to be genetically close to Koshu-Sanjaku, a minor Japanese vinifera table variety, but its profile matches no European parent. For most of its history Koshu was a table grape and a source of sweetish, simple wine. Modern dry white winemaking began to take hold in the 1980s, when producers introduced lees ageing and cooler fermentations. The turning point for export came in 2010, when Koshu was entered in the OIV list of vine varieties, which permitted the name on labels of wine sold in the European Union. A first shipment of Koshu-labelled wine left for London that year. Yamanashi became Japan's first wine geographical indication in 2013.
Viticultural Characteristics
Koshu is vigorous, buds mid to late in the season and ripens late, with harvest typically running from late September into October. Its bunches carry large, thick-skinned berries, a trait inherited from its table-grape past that helps it withstand humidity. It copes with botrytis better than most vinifera in Japan's damp climate, but it is susceptible to downy and powdery mildew, and the growing season coincides with the rainy period and typhoon risk. Overhead pergolas (tanazukuri) have long been standard because they lift fruit away from the soil, improve airflow and absorb the vine's vigour. Because pergola yields are high, quality-focused producers have trialled vertical shoot positioning, lower yields and rain protection, and Grace Wine in Yamanashi has moved some of its Koshu onto VSP trellising.
Wine Styles & Characteristics
The traditional modern style is a dry, unoaked white fermented cool in stainless steel, pale in colour, lightly aromatic and best drunk within a year or two. Many producers now leave the wine on its lees (sur lie), a practice Mercian adopted in the 1980s, to add texture and a savoury, umami-like depth. Barrel-fermented versions, among them those from Katsunuma Jozo, show more weight and a creamy finish, while the grape's thick skins make it a candidate for skin contact: amber or orange wines extract colour, phenolics and red-fruit notes from the pink skins. Sparkling Koshu, made by both tank and bottle fermentation, is a growing category. Off-dry and sweet wines also exist, and are the older domestic tradition. Koshu is generally unblended and appears as a varietal wine, though it can be used in blends with other white varieties.