Japanese red bean soup with mochi, often called zenzai or oshiruko depending on the region and style, is a warm, sweet dessert made with azuki beans and chewy rice cakes. The beans simmer into a gently thick broth, while toasted mochi adds a soft, stretchy contrast; regional and family versions vary in sweetness and texture.
Ingredients
- 1 cup (200 g) dried azuki beans
- 6 cups (1.4 L) water, for the first boil
- 5 cups (1.2 L) fresh water, for simmering, plus up to 2 cups (480 ml) hot water as needed
- ½ cup (100 g) granulated sugar, or up to ⅔ cup (135 g) for a sweeter soup
- ¼ teaspoon (1.5 g) fine salt
- 4 pieces packaged kirimochi, about 7 ounces (200 g) total; substitute plain, unsweetened mochi if needed
Instructions
- Rinse the beans. Pick through the azuki beans and discard any shriveled beans or small stones. Rinse them in a sieve under cool running water, rubbing them lightly with your fingers. Put the beans in a medium, heavy-bottomed saucepan with 6 cups (1.4 L) water. The beans will expand as they cook, so use a pot with room for them to move freely.
- Give the beans a first boil. Bring the water to a boil over medium-high heat and boil the beans for 5 minutes. Drain them in a colander and rinse briefly. This first boil helps clear some of the surface starch and creates a cleaner-tasting broth. It is a common preparation, though not every household or regional method uses it.
- Simmer until tender. Return the beans to the pot and add 5 cups (1.2 L) fresh water. Bring to a boil, then lower the heat so the beans simmer gently. Partially cover the pot, leaving a small gap for steam to escape, and cook for about 70 minutes. Check around the 55-minute mark: the beans are ready when they are very tender and can be easily squashed against the side of the pot with a spoon. If the water level drops until beans are exposed, add some of the reserved hot water. Keep the simmer gentle; a hard boil can split the beans before their centers soften.
- Sweeten the soup. Stir in the sugar and salt only after the beans are tender. Simmer gently for 10 minutes, stirring occasionally until the sugar dissolves and the broth tastes rounded rather than sharply sweet. Taste and add a little more sugar if you prefer a dessert-like finish. If the soup becomes thicker than you like, loosen it with a splash of hot water. The beans and broth should be spoonable, not as thick as a bean paste.
- Toast the mochi. While the soup finishes, toast the mochi in a toaster oven or under a broiler until puffed and lightly browned, about 6 minutes, turning once if your appliance browns unevenly. Watch closely near the end because mochi can go from toasted to scorched quickly. You can also cook it in a dry skillet over medium-low heat, turning it as it puffs and develops golden spots. Follow the package directions if they give a different method or timing.
- Serve hot. Divide the hot azuki soup between four bowls and add one toasted mochi piece to each. If the rice cakes are large, cut them into smaller pieces with a lightly oiled knife or kitchen scissors before serving. Serve promptly, while the mochi is soft and stretchy.
Tips
- Do not add the sugar early. Sweetener can slow the softening of beans, so wait until the azuki are tender before stirring it in. If the beans are still firm after the expected simmer, continue cooking them in plain water and check every 10 minutes.
- Keep extra hot water nearby. Beans absorb water as they simmer, and the amount lost to evaporation varies with the pot and stove. Adding hot water maintains an even simmer without cooling the beans abruptly. Add it a little at a time so the finished soup does not become watery.
- Adjust the sweetness gradually. The listed half-cup of sugar gives a gently sweet result. Start there, taste after it dissolves, and add more in small increments if wanted. Brown sugar can replace granulated sugar, but it adds a deeper, molasses-like note and darkens the broth.
- Toast the mochi separately. Rice cakes left sitting in the soup soften and can become very sticky. Toasting them just before serving gives you browned edges and a chewy center. Take care when eating mochi: it is elastic and sticky, so cut it into manageable pieces, particularly for young children and older adults.
Serving Suggestions
Serve zenzai as a small dessert or an afternoon snack, ideally just after the mochi is toasted. The soup is filling, so a modest bowl is often enough after a meal. A small cup of unsweetened green tea, hojicha, or roasted barley tea makes a pleasant contrast to the beans’ sweetness. For a simple Japanese-style dessert spread, offer the soup alongside fresh fruit or a few plain rice crackers rather than another rich sweet.
Check the consistency before ladling. Some people prefer a clear, fairly loose broth with whole beans; others like to press a few beans against the pot to make the soup thicker and more rustic. If you want a smoother bowl, mash a portion of the cooked beans with the back of a spoon and stir them back in. Keep most of the beans intact if you want a more varied texture. Serve the mochi on top rather than stirring it through the pot, so each person can decide how much to mix into the soup.
Variations
Use canned azuki beans for a quicker version. Choose plain, unsweetened canned beans, drain and rinse them, then simmer them with about 3 cups (710 ml) water for 15 to 20 minutes before adding sugar and salt. The beans may be softer and the broth less developed than with dried beans. Canned sweetened azuki paste is another option, but it is much sweeter and thicker; dilute it gradually with hot water and taste before adding any extra sugar.
Make the broth smooth. For a less rustic texture, cook the beans until very soft, then press some or all of them through a fine sieve or blend carefully with an immersion blender. Add hot water to reach your preferred thickness. A fully smooth version is closer to a sweet bean soup made with strained azuki paste than the whole-bean preparation here.
Try a different topping. If packaged kirimochi is unavailable, use plain, unsweetened mochi from a Japanese or other East Asian grocery store. Do not substitute sweet rice pudding or flavored mochi sweets, which have different textures and may make the soup overly sweet. In a pinch, small dango or plain rice dumplings can be served with the soup, though their texture is softer and more pillowy than toasted mochi.
Choose a regional style. The names zenzai and oshiruko are used differently across Japan, and the distinction can refer to details such as whether the beans are whole or strained. At home, the terms and preferred textures vary. This whole-bean recipe is one practical style rather than a claim that there is a single definitive version.
Storage and Reheating
For best texture, store the azuki soup and mochi separately. Refrigerate the soup within 2 hours of cooking in a covered container; it keeps for 3 to 4 days. The mochi is best toasted fresh. If you have leftover toasted mochi, refrigerate it separately and expect it to firm up; it may soften when reheated, but it will not have quite the same toasted exterior.
Reheat the soup gently in a saucepan over medium-low heat, stirring now and then. Add a splash of water if it has thickened in the refrigerator, and heat until steaming throughout. If using a microwave, cover the bowl loosely, heat in short intervals, and stir between intervals to avoid uneven hot spots. Reheat only the portion you plan to eat. Toast fresh mochi and add it to the warmed soup just before serving. You can freeze the soup without the mochi for up to 2 months in a freezer-safe container; thaw it overnight in the refrigerator and reheat gently. Its texture may be a little softer after freezing.
Frequently Asked Questions
Are zenzai and oshiruko the same thing?
They are closely related names for sweet azuki bean soup, but their use and the distinctions between them vary by region. Some versions feature whole beans, while others are smoother or made with strained bean paste. This recipe uses whole beans, and either name may be familiar depending on where you encounter it.
Do I have to soak azuki beans overnight?
No. Small azuki beans generally cook without an overnight soak, which is why this recipe uses a first boil followed by a long simmer. Older beans can take longer to soften, so judge doneness by their texture rather than relying only on the clock. If you prefer to soak them, refrigerate them in plenty of water overnight and expect the simmering time to be shorter.
Why are my beans still firm?
They may need more time, especially if the beans have been stored for a long time. Keep them at a gentle simmer in water and test again every 10 minutes. Avoid adding sugar until they are tender, and make sure they have not run low on water. A rapid boil is not a shortcut; it can break the skins while leaving the centers firm.
Can I make the soup less sweet?
Yes. Start with ⅓ cup (about 67 g) sugar instead of the listed ½ cup, then taste after it has dissolved and add more only if you want it. The amount of sweetness is a matter of preference, and reducing it does not change the cooking method. Remember that sweetened canned beans or bean paste may already contain a considerable amount of sugar.
Can I cook the mochi directly in the soup?
You can warm plain mochi in the soup, but toasted mochi gives the bowl more texture and is less likely to turn the whole pot sticky. If you do simmer it in the soup, add it only near the end and cook until soft, following the package directions. Avoid storing leftover mochi in the soup because it continues to absorb liquid and becomes very soft.