The starch, which is called gok fun in China and ko fen in Japan, comes from the root. Tsuji (1980) describes its good properties thus:
As a thickener, kuzu starch—extracted from the root of the vine—is excellent: it produces a sparkling, translucent sauce and adds shiny gloss to soups. It has a gentle pleasant aroma, and does its work at fairly low temperatures. Because it is an alkali, it balances acidity, such as found in sweets. Dusted over foods to be deep fried, it yields a light, crisp, almost crystalline snow-white coating.