Koshian

First you need to cook the beans. It's important to soak the beans and cook them carefully to maintain proper texture. When the beans are cooked, sugar is added and the mixture is reduced to a syrup consistency. Follow the attached recipe.

Tsubuan

These sweetened red beans are commonly used in Japanese sweets.

Mash the whole beans slightly to break them up.

Tsubushian

Anko paste is a simple paste of sweetened red beans that appears in a lot of Japanese desserts. There are 3 varieties or stages referring to the texture or basically just how much you squished the beans. Tsubuan refers to whole unmashed bean paste. Tsubushian is a lightly mashed bean paste as in the image above. Koshian is mashed and sieved bean paste with no visible bean chunks.

Now, you need to press the beans through a fine sieve. This can be quite a bit of work. The contents of the bean are pressed through, while the sheath of the bean mostly gets caught in the sieve.

The result is a fine, smooth sweet bean paste that can be used in Japanese desserts and confectionery. It will also store well in the freezer for at least a month.