Tofu arrived in Japan from China in the Nara period (710–794 CE) through Buddhist temple food networks; the use of sea water bittern (nigari) as the Japanese coagulant reflects Japan's coastal sea salt production as the dominant mineral salt source; the development of regional styles accelerated from the Edo period when commercial tofu shops became a fixed feature of Japanese urban food culture; the Kyoto kinugoshi style was developed specifically for the delicacy requirements of kaiseki cuisine
Tofu production from soymilk requires the coagulation of soy proteins (principally glycinin and beta-conglycinin) by adding a coagulant to hot soymilk — the traditional Japanese coagulant is nigari (苦汁 — bittern), the mineral-rich byproduct of sea salt production that contains primarily magnesium chloride with calcium and potassium salts. The mineral composition of nigari directly affects tofu flavour: magnesium chloride produces a slightly bitter, complex flavour distinct from calcium sulphate (gypsum)-set tofu which is milder and larger-celled. Regional styles: Kyoto kinugoshi (silk tofu) is made with more soymilk and less nigari, producing an extremely soft, delicate custard-like texture; Kyushu island tofu is firmer with a higher protein density from higher bean-to-water ratios; Okinawa tofu (shimadofu) is exceptionally firm, suitable for frying without crumbling. Making tofu at home: prepare soymilk from dried soybeans (soak 10 hours, grind with water, heat, and strain through muslin); heat to 78°C, add nigari dissolved in warm water (5g per litre soymilk), stir gently once, cover and allow to stand 5–10 minutes undisturbed; the curds set silently; ladle gently into muslin-lined mold and press for 20–30 minutes for firm tofu, 5 minutes for softer.
Temperature precision (78°C) is the protein denaturation threshold — too cold, incomplete coagulation; too hot, tough texture; single gentle stir after nigari addition — over-stirring breaks curds producing grainy texture; the standing period must be undisturbed — vibration prevents proper coagulation; pressing duration determines water content and firmness; soymilk quality (higher bean concentration) produces better tofu.
The 'flower curds' test: properly nigari-set soymilk develops tofu-hua (silken curds) that can be eaten directly from the pot without pressing — the softest form of tofu, served in Okinawa with Okinawan brown sugar syrup as a dessert (tofuyo); professional tofu makers make soymilk from dried soybeans with a specific bean-to-water ratio of 1:9 for kinugoshi and 1:7 for firm tofu; the golden soymilk should smell clean and sweet — if it smells beany or bitter, the heating stage was insufficient.
Adding nigari at boiling temperature (100°C) — produces grainy, rubbery tofu; over-stirring — breaks the coagulating gel network; pressing with too much weight (extracts too much moisture, changes texture from intended); soymilk prepared from low-quality or old soybeans — tofu from poor soymilk cannot be rescued by technique.
Tsuji, Shizuo — Japanese Cooking: A Simple Art; Andoh, Elizabeth — Kansha