Anko: Tsubu-an, Koshi-an, and Shiro-an — The Three Pillars of Red Bean Paste

Overview

Anko — sweetened bean paste — is the foundational filling ingredient in Japanese wagashi and a defining element of Japanese confectionery culture, appearing in everything from summer kakigori shaved ice to autumn manjū buns and winter oshiruko sweet soup. Understanding the three primary anko types — tsubu-an, koshi-an, and shiro-an — is essential for any pastry professional working with Japanese ingredients. Tsubu-an (粒あん) is whole-bean paste in which the azuki beans are simmered until tender but retain their shape, then crushed lightly and sweetened, leaving visible bean pieces and skins in the paste. Its texture is chunky and rustic, with a deeper, earthier flavour than refined pastes because the skins contribute tannins and colour. Tsubu-an is used in dorayaki, taiyaki, daifuku mochi, imagawayaki, and ohagi — popular confections where textural interest and robust flavour are valued. Koshi-an (こしあん) is the refined paste produced by cooking azuki beans until completely soft, then passing them through a fine sieve (uragoshi) to remove all skins, yielding a smooth, silky, burgundy paste of extraordinary refinement. Koshi-an has a more delicate, cleaner sweetness than tsubu-an — the removal of the bitter tannin-bearing skins eliminates astringency and creates the paste preferred for high-end wagashi such as nerikiri, higashi fillings, and tea ceremony confections. The sieving process is labour-intensive and reduces yield (skins are discarded), making koshi-an more expensive. Shiro-an (白あん) uses white beans (typically shiro ingen — Great Northern or other white navy beans, or tora mame — sometimes shiro azuki) rather than red azuki, producing an ivory-coloured paste with a milder, more neutral sweetness than either red bean variant. Shiro-an is valued as a base paste in nerikiri — the highly sculptable premium wagashi — where it is mixed with gyuhi (glutinous rice paste) and kneaded to a modelling consistency that holds intricate forms. Shiro-an's neutral colour also accepts natural food colourings — matcha, sakura, charcoal — allowing wagashi artisans to create the full seasonal colour palette seen in finest teahouse sweets. Each paste type requires distinct cooking techniques, sugar ratios, and moisture management to achieve optimal workability.

Flavour Context

Tsubu-an: earthy, slightly tannic, robust sweetness with textural variation; Koshi-an: clean, refined, silky sweetness with zero astringency; Shiro-an: mild, creamy, neutral sweetness — a flavour canvas

Key Principles

{"Tsubu-an: crush lightly after cooking to retain skin texture and rustic character — do not over-process","Koshi-an: pass through fine uragoshi sieve while beans are hot — easier to pass when warm; cold beans clog sieves","Shiro-an: white beans require longer soaking and more careful heat management to prevent discolouration during cooking","Sugar addition timing matters: add sugar in stages after beans are soft — adding early toughens cell walls and prevents full softening","The desired moisture level differs by application: firmer paste for moulding (nerikiri), softer for dorayaki fillings, loosest for oshiruko soup","Tane mizu (the boiling water discarded after first cook) removes harsh tannins — essential for koshi-an, optional for rustic tsubu-an"}

Pro Tips

{"Test anko consistency by letting a small amount cool — paste thickens significantly as it cools, so cook to looser than desired final texture","For shiro-an used in nerikiri, dry the paste in a covered pan over low heat after sweetening — evaporating moisture improves moulding stability","A small amount of salt (0.2–0.5% of bean weight) enhances sweetness perception and rounds the flavour","Rest finished anko covered in the refrigerator for at least 4 hours — flavours integrate and texture stabilises","For tsubu-an with maximum bean integrity, use the 'hitachi-ni' technique: simmer with minimal water until nearly dry, add sugar, then finish gently"}

Common Mistakes

{"Adding sugar to hard beans — prevents full softening and produces gritty, dense paste","Over-sieving tsubu-an — eliminates the textural character that distinguishes it from koshi-an","Under-sieving koshi-an — visible skin fragments are unacceptable in premium wagashi","Cooking shiro-an with iron-rich utensils — iron discolours white beans to grey","Adding too much sugar too quickly — creates a crust on the paste surface rather than uniform incorporation","Skipping the tane mizu removal stage for koshi-an — retains bitter astringency that undermines the refined character of the paste"}

Source

Wagashi and the Art of Japanese Confectionery — Masakazu Hori

Cross-Cuisine Parallels

• {'cuisine': 'Korean', 'technique': 'Pat (팥) — sweetened red bean paste used in patbingsu, tteok, and hotteok', 'connection': 'Parallel azuki bean paste tradition using virtually identical cooking methods; Korean versions are often less sweet and more likely to retain rustic tsubu-an style'}
• {'cuisine': 'Chinese', 'technique': 'Dou sha (红豆沙) — red bean paste in mooncakes, tang yuan, and bao fillings', 'connection': 'Shared azuki-based paste culture across East Asia; Chinese versions commonly include lard for richness and shelf stability, unlike Japanese anko'}
• {'cuisine': 'French', 'technique': 'Haricot bean or chestnut purée in tarts and Mont Blanc', 'connection': 'European pastry tradition of legume and nut-based sweet purées as fillings; chestnut crème in Mont Blanc shares the texture philosophy of koshi-an — smooth, refined, single-flavour pastes'}