Japan (ancient use of adzuki in religious offerings; refined as wagashi filling through Buddhist temple and imperial court confectionery traditions)
Anko (餡子, sweet red bean paste) is the foundational filling and coating material of Japanese wagashi confectionery — made from adzuki beans (Vigna angularis) simmered with sugar until soft, then processed to either of two textures that define its use. Tsubuan (粒餡) retains the whole or partially intact bean grains, producing a rustic, textured paste with visible bean skin and grain — typically used in ohagi, imagawayaki, and less formal confections. Koshian (漉し餡) is strained through a fine sieve after cooking to remove all skins and fibre, producing a completely smooth, silky, uniform paste — used in nerikiri wagashi, mochi daifuku, and formal confections where complete textural refinement is required. A third form, sarashian (晒し餡), is koshian that has been further dried to a powder or dehydrated form for extended storage. The quality of anko depends fundamentally on adzuki bean quality — Tokachi (北海道十勝地方) in Hokkaido produces Japan's most prized adzuki, with high sugar content and delicate skin. Making anko requires the precise water-absorption and cooking management that prevents the beans from bursting (which releases starch and muddles the colour) while achieving complete tenderness. The final sugar content of quality anko is calibrated — typically 70–100g sugar per 100g dried beans — to balance sweetness without cloying.
Earthy, mildly sweet, subtly astringent from adzuki skins; calibrated sweetness; salt amplifies the bean's natural character; tsubuan has more grain presence, koshian is perfectly smooth
{"Tsubuan: whole or broken bean grains retained; rustic, textured, less formal applications","Koshian: completely smooth strained paste; formal confectionery, nerikiri, daifuku","Initial blanch: adzuki simmered and discarded once to remove bitter skin compounds before main cook","Slow sugar incorporation: add sugar in stages to prevent crystallisation and maintain smooth texture","Tokachi adzuki: Hokkaido-produced premium variety; thinner skin, higher sugar content, finest paste"}
{"The first blanch water (discarded after 5 minutes of initial boiling) is dramatically darker than subsequent water","Finish anko over direct heat while stirring with a wooden spatula — the slight caramelisation at the edges adds depth","Test consistency: anko should hold a peak on a spatula but flow slowly when tilted","Add a small amount of salt to finished anko — it amplifies sweetness and rounds the bean flavour"}
{"Skipping the initial blanch — bitter tannins from skins compromise the final paste flavour","Boiling hard after adding sugar — sugar crystallises and paste becomes grainy","Over-reducing — paste becomes too stiff to pipe or fill; must remain workable at room temperature","Using cheap adzuki — skin quality determines whether koshian strains smoothly or remains gritty"}
Tsuji Shizuo, Japanese Cooking: A Simple Art