Koshian vs Tsubuan: Two Styles of Red Bean Paste, Explained
Order two pieces of wagashi that both list “anko” as the filling, and you can still end up with two completely different textures. The difference almost always comes down to one production choice: whether the bean skins stayed in or got strained out.
The actual difference
Anko (our full guide to anko covers where it actually comes from) starts the same way for both styles: azuki beans simmered until soft, then sweetened. From there, the two paths split.
Koshian (漉し餡, “strained paste”) pushes the cooked beans through a fine-mesh strainer or cloth, removing every skin and fragment, then kneads the result into a smooth, uniform paste. That straining step is genuinely labor-intensive, which is part of why koshian is often treated as the more refined, higher-effort version.
Tsubuan (粒餡, “grain paste”) skips the straining. The beans are simmered gently enough to hold their shape, then lightly mashed or left mostly whole, skins and all, for a chunkier texture with more visible bean structure and, many wagashi makers argue, a more direct bean flavor since nothing gets filtered out.
Anko itself isn’t always red, either. Shiro-an (白餡, “white paste”) follows the same koshian or tsubuan production logic, straining or not straining, but starts from white beans like lima or cannellini beans instead of azuki. The result is milder and more neutral in flavor, with a pale ivory color that takes food coloring cleanly. That’s exactly why wagashi makers reach for shiro-an as the base for hand-shaped seasonal nerikiri sculptures: a colored flower or leaf needs a base that won’t fight the added color or compete with azuki’s own reddish-brown tone.
A real regional pattern
Neither style is regionally exclusive, but there’s a genuine, well-documented pattern in at least one classic sweet: sakuramochi. Kanto-style sakuramochi, with its thin, crepe-like wrapper, is typically filled with koshian. Kansai-style sakuramochi, made with a coarser, chewier rice-based wrapper, is typically filled with tsubuan. The pattern isn’t a strict rule across every wagashi shop in Japan, but it’s consistent enough to be a genuinely useful signal when a listing specifies regional style.
Which one you’re actually buying
A smooth, glossy, uniform filling with no visible bean texture is koshian. A filling with visible whole or partly-crushed beans and a coarser bite is tsubuan. “Ogura-an” or “Kyoto-style anko” on a listing usually points to the koshian-plus-whole-bean mixed style, not a simple blend of the other two, and “shiro-an” or “white bean paste” means the same production split has been applied to white beans instead of azuki.
Beyond sakuramochi’s regional pattern, there’s a looser convention by sweet type, though it’s followed less strictly than the Kanto/Kansai split. Tsubuan tends to be the more common traditional choice for dorayaki and manju, while daifuku genuinely goes either way depending on the maker, with no strong convention either direction. Ohagi and botamochi add a third explanation entirely, tied to harvest timing rather than region or sweet type. None of this makes one style more “authentic” than another. Both koshian and tsubuan are long-established, widely used styles, and the right choice for a given purchase comes down to texture preference, not correctness.
Frequently asked questions
What's the actual difference between koshian and tsubuan?
Whether the azuki bean skins are removed. Koshian is strained smooth through a fine mesh or cloth, removing all skins and fragments. Tsubuan keeps the beans whole or lightly mashed, skins included, for a chunkier texture.
Which is more traditional, koshian or tsubuan?
Neither is more traditional than the other; both are long-established styles used across wagashi. A third named style, ogura-an, mixing koshian with whole sugar-simmered Dainagon beans, takes its name from Kyoto's Mount Ogura growing region.
Is there a regional preference for koshian vs tsubuan?
Yes, most visibly in sakuramochi: Kanto-style versions typically use koshian, while Kansai-style versions typically use tsubuan. It's a real pattern, though not an absolute rule across every wagashi maker.
What is ogura-an?
A named third anko style that mixes koshian with whole sugar-simmered azuki beans, usually the large Dainagon variety, for texture without full crushing. It's named after Mount Ogura in Kyoto's Saga district, historically known for growing quality Dainagon azuki.
Which style tastes more like the actual bean?
Many wagashi makers describe tsubuan as having a more direct bean flavor, since nothing gets strained out. Koshian's smoother process can mute that slightly, though both are made from the same base ingredient and the difference is subtle.
What is shiro-an?
White bean paste, made the same way as koshian or tsubuan but starting from white beans like lima or cannellini beans instead of azuki. It has a milder, more neutral flavor and a pale color that takes food coloring cleanly, which is why it's often used as the base for hand-colored seasonal nerikiri sweets.
The short version
Koshian and tsubuan are both sweetened azuki bean paste; the split is entirely about whether the bean skins are strained out (koshian, smooth and labor-intensive) or left in (tsubuan, chunkier and more direct in flavor). A third named style, ogura-an, mixes koshian with whole sugar-simmered Dainagon beans and takes its name from Kyoto’s Mount Ogura growing region, and the same production logic applies to white beans as shiro-an, valued for its mild flavor and colorable pale base. There’s a real regional pattern, most visible in Kanto-style koshian sakuramochi versus Kansai-style tsubuan sakuramochi, but neither style is more correct than the other.