Kudzu Starch

Kuzuko is the pure starch isolated from the tuberous root of Pueraria lobata (Japanese kudzu). The traditional 'Yoshino-zarashi' method, practised in Yoshino (Nara) since the Edo period, crushes winter-harvested roots, washes the starch fraction repeatedly with cold spring water over 30–90 days to settle and re-suspend the starch, then air-dries the white blocks. The process yields a high-purity starch with characteristic gelling and thermo-reversible properties.

Three classic uses: kuzu-mochi (chilled translucent jelly cubes coated in kinako and kuromitsu), kuzu-kiri (cold dessert noodles served with kuromitsu), and kuzu-yu (a hot, viscous starch drink consumed during winter or convalescence). Kuzuko is also used as a thickener for ankake sauces, where it gives a glossier, more elastic texture than potato or corn starch.

The same plant species (Pueraria lobata) supplies both. The dried root used in Kampo formulas under the name 葛根 (kakkon) — for example in Kakkonto (葛根湯) — is regulated as a crude drug under Japan's Pharmaceutical and Medical Device Act and is processed differently from the food-grade starch. Kuzuko is the isolated starch fraction; kakkon is the whole dried root used in herbal preparations.

There is no Geographical Indication (GI) registration under Japan's Act on Protection of the Names of Specific Agricultural, Forestry and Fishery Products for 'Yoshino kuzu' as of public registry data, but the term is associated by local industry convention with starch processed in the Yoshino area. Some Yoshino producers are protected by individual trademarks. Pure kuzuko on the Japanese market is often labelled '本葛 100%' (100% hon-kuzu), distinguishing it from blends of kuzu starch with sweet potato or other starches.