Japan — konnyaku production in Japan is documented from at least the Nara period (8th century), introduced from China where the konjac corm was processed for food. The Kanto and Shimotsuke regions (particularly Gunma Prefecture) became the primary production centres and remain Japan's dominant konnyaku producers. The use of alkaline water to set the glucomannan gel was developed through experimentation with wood ash solutions.
Konnyaku (蒟蒻, konjac, Amorphophallus konjac) is a gelatinous food made from the starchy corm of the konjac plant — processed into a firm, rubbery, virtually zero-calorie food that has been a staple of Japanese cooking for over 1,500 years. Konnyaku is remarkable for its composition: 97% water and glucomannan (a soluble dietary fibre with unique properties — it forms a strong, stable gel in the presence of alkali, which is why konnyaku production uses alkaline wood ash water or calcium hydroxide). The primary forms: ita-konnyaku (板蒟蒻, block konnyaku) — standard form, greyish-brown; shirataki (白滝, white waterfall noodles, a common name for konnyaku noodles) — fine konnyaku noodles used in sukiyaki and nabe; ito-konnyaku (糸蒟蒻, thread konnyaku) — thicker noodle form. Its flavour is minimal; its value is textural and as a medium for absorbing other flavours.
Konnyaku's own flavour is nearly absent — a faint, slightly earthy, alkaline background that recedes completely in seasoned preparations. Its value is entirely textural and functional: the rubbery, bouncy, almost springy resistance when bitten; the way it retains this texture through extended simmering while absorbing surrounding flavours; and its ability to provide satisfying bulk and chew without calories. In oden after extended simmering: the konnyaku has absorbed the amber dashi-soy broth completely — each bite releases the broth's flavour while the konnyaku's own resistance provides a contrasting texture to the soft daikon and tender fish cakes around it.
Konnyaku preparation: before use in most preparations, konnyaku benefits from pre-treatment to remove the slightly alkaline flavour: (1) Boil briefly (3–5 minutes) in plain water to remove excess surface alkalinity; (2) Tear or cut — konnyaku torn with the hands (rather than cut with a knife) has a rougher surface that absorbs broth more effectively; (3) Dry-fry without oil in a hot pan until slightly shrunken and dry on the surface — this creates micro-pores that significantly increase flavour absorption in subsequent simmering. The preparation for nimono: konnyaku that has been dry-fried absorbs dashi-soy broth during simmering far more effectively than untreated konnyaku.
The best technique for konnyaku in oden: score the block surface in a diamond crosshatch pattern (2–3mm deep, 5mm intervals); pre-boil 5 minutes; add early to the oden broth (konnyaku requires 3+ hours of simmering to fully absorb the broth). After extended oden simmering, the scored konnyaku becomes deeply flavoured throughout, with the dashi-soy completely penetrating the previously neutral matrix. Konnyaku sashimi (tsukimi konnyaku): thin-sliced white konnyaku served raw with grated ginger and soy sauce — the cool, slightly gelatinous texture and mild flavour make it a palate-refreshing 'sashimi' that is entirely plant-based.
Adding shirataki noodles directly to a dish without pre-boiling — the alkaline compounds create an off-flavour. Not pressing konnyaku before use — untreated konnyaku releases water during cooking, diluting the surrounding sauce. Using konnyaku in preparations where its rubbery texture is unwanted — konnyaku is a textural element, not a neutral background.
Washoku — Elizabeth Andoh; Japanese Cooking: A Simple Art — Shizuo Tsuji