Koshian vs Tsubuan: Japan's Two Kinds of Sweet Red Bean Paste

Smooth or chunky, sieved or whole: the choice between koshian and tsubuan shapes the feel of countless Japanese sweets.

Published October 21, 2026 at 9:13 PM JST | By Tokyo Paul

Quick answer: Koshian is smooth red bean paste made by sieving out the bean skins, while tsubuan keeps the beans whole or nearly whole in a sweet paste. Both are called anko and both use azuki beans and sugar. Koshian feels silky and refined, tsubuan feels hearty and textured, and many Japanese sweets are sold in both versions.

Few ingredients show up in Japanese sweets as often as anko, the sweet red bean paste tucked inside buns, pancakes, rice cakes, fish-shaped cakes and festival treats. Visitors soon notice that shops offer it in two forms, and sometimes ask customers which one they prefer. The names look intimidating, but the difference is easy to understand once you know what is removed or left in. This guide explains both pastes, how they are made, which sweets use them and how to choose when you are standing at a counter.

The Quick Difference in Everyday Terms

The easiest way to remember it is by texture. Koshian is the smooth one, like a thick pudding or a fine spread. Tsubuan is the chunky one, with whole beans or large pieces in a sweet, soft paste. The Japanese word tsubu means grain or granule, which hints at the idea.

Both begin with the same ingredient, azuki beans, and both are cooked with sugar. The only major difference is what happens to the skins. In koshian they are removed, and in tsubuan they stay. That single step changes the mouthfeel, the look and even how the sweets are shaped, which is why the two have each earned loyal fans in Japan.

How Koshian Is Made

According to reference descriptions of red bean paste, koshian is prepared by boiling the beans, mashing or grinding them, and passing the mixture through a sieve to remove the skins. In the traditional smooth process described by sources, the beans are boiled without sugar, mashed into a slurry, strained and then squeezed dry before sweetening, and oil or lard is often added during cooking. The kanji for koshi means to strain or filter.

The result is a fine, uniform paste with a mellow color. Because the skins are gone, the flavor is clean and the surface is silky. Wikipedia describes koshian as the most common type of anko in Japan, and it makes a smooth filling that spreads evenly through a mochi wrapper or a pastry.

How Tsubuan Is Made

Tsubuan is closer to the original beans. Whole azuki beans are boiled with sugar and otherwise left intact, so the skins and the shape of the beans remain, and the paste keeps its distinctive texture.

Each spoonful has a soft, slightly grainy bite, and the whole beans give a more rustic, home-style feel. Some people find that the flavor shows a little more of the earthy bean character that sieving smooths away in koshian. The difference is often compared to chunky versus smooth peanut butter, though that is only a rough guide.

The Other Names You May See

Beyond these two, you may meet a few close relatives. Tsubushian is paste in which beans are mashed after boiling, so it is another variation between the two main types. Ogura-an is a mixture of koshian and tsubuan, and its name refers to Mount Ogura in western Kyoto. Sarashian starts from beans that are dried and then reconstituted with water.

Another important member of the family is white bean paste, shiroan, which uses white beans instead of azuki and is used for refined sweets such as nerikiri. Strictly speaking, the word an is the general term for sweet mashed paste, anko is the common word for the red bean version, and azukian points directly to red bean paste. The same idea exists across East Asia, with Chinese and Korean names for their own red bean pastes.

Where You Will Meet Each One

Anko is used in anmitsu, anpan, daifuku, dorayaki, manju, yokan and taiyaki, and the list also includes imagawayaki, monaka and many others. Shops often offer a choice. At a shop that sells filled cakes, you may see both options listed, or the staff may ask which kind you want.

Anpan, a sweet roll that originated in Tokyo bakeries in the Meiji era, is typically filled with red bean paste. Dorayaki, two small pancakes sandwiching bean paste, is another everyday sweet and is famously the favorite food of the cartoon character Doraemon. Neither is tied to a single paste, and fillings vary by maker, so reading the sign is the surest guide.

How to Choose Between Them

If you prefer sweets that feel refined and silky, start with koshian. It pairs well with a delicate rice wrapper and does not distract from the dough. If you enjoy a bite and a more homemade feeling, choose tsubuan, which gives the filling its own personality.

There is no right answer, and personal preference is part of the fun. Some people pick based on the sweet itself: a soft wrapper may feel best with smooth paste, while a crisp shell may stand up well to chunky beans. A good plan is to try the same sweet in both styles from one shop and compare. Remember that sweetness levels differ by maker, so taste is the best teacher.

Why Azuki Beans Matter in Japan

Azuki is a small red bean written with the characters for small bean (read shozu in Chinese-derived style), in contrast to daizu, the soybean. Wikipedia notes that seed remains found in Japan date back several thousand years, and it describes azuki as the second most important legume in Japan after soybean. It is a core ingredient in confections and also in sekihan, red bean rice served on auspicious occasions.

Because the bean carries those festive associations, it appears in sweets for many celebrations. The Government of Japan's Highlighting Japan series has described the red azuki on a summer sweet called minazuki as a traditional charm to ward off evil spirits and bring good health. In this way anko is both an everyday filling and a cultural symbol.

Ordering Tips and Dietary Notes

When you shop, look for the kanji for koshi (漉し) or tsubu (粒) on labels, or simply ask the staff which paste a sweet contains. Pictures and sample pieces in display cases often show the difference clearly. Stores and department store food halls are used to curious visitors, so a question is welcome.

Ingredients vary by maker, and recipes can include additions beyond beans and sugar. Anyone with allergies or dietary requirements should check the ingredient list or ask at the counter before buying. A gentle rule is to treat the label as the final word and to confirm with staff when you are unsure.

Taking the Next Step in Anko Tasting

Once the two basics are familiar, tasting becomes an enjoyable game. Try a plain mochi with koshian, then the same mochi with tsubuan. Notice how a cup of unsweetened green tea changes the experience.

The difference between koshian and tsubuan is small on paper and large on the tongue. It is also a reminder that Japanese sweets often turn on subtle choices about texture. Whichever paste you reach for, you are tasting one of the central ingredients of Japanese confectionery.

Want to go deeper? Tokyo Paul's book 30 Japanese Wagashi, Seasonal Sweets, and Childhood Classics is available on Amazon.

Frequently Asked Questions

What is the difference between koshian and tsubuan?

Koshian is smooth red bean paste made by sieving out the bean skins, while tsubuan keeps whole or nearly whole beans in a sweet paste. Both use azuki and sugar. Koshian feels silky, and tsubuan feels chunky and rustic. Most shops that sell filled sweets offer one or both.

Which red bean paste is more common in Japan?

Reference descriptions call koshian the most common type of red bean paste in Japan. Even so, tsubuan is widely available and popular, and many sweets are offered in both versions. Personal and regional taste varies, so the best approach is to try both and decide for yourself.

What is ogura-an?

Ogura-an is a mix of koshian and tsubuan, combining smooth paste with whole beans. The name refers to Mount Ogura in western Kyoto. It gives a balance of silkiness and texture, and you may see the word on menus and labels.

Further Reading

To explore further, see Red bean paste, Adzuki bean and Dorayaki.

Keep Exploring

More guides from Tokyo Paul: Yokan and Manju: Bean Paste Sweets with Centuries of Craft, Imagawayaki: Japan's Warm Round Cakes Filled with Sweet Bean and Taiyaki: The Fish-Shaped Cake Japan Adores.