Desserts
Zenzai (Sweet Red Bean Soup with Toasted Mochi)
A hot, gently sweet soup of whole azuki beans poured over toasted rice cakes that turn crisp outside and stretchy inside. A Japanese winter favourite, and simple to make once the beans are on.
- Serves 4
- Prep 10 min
- Cook about 1 hr 45 min
- Japanese
Method
Tip the beans into a sieve, rinse them under the cold tap and pick out any that float or look shrivelled or split.
Put the beans in a large pan, cover generously with cold water and bring to the boil. Boil for 3 minutes, then drain in the sieve and rinse. This quick first boil takes away some of the beans’ slightly bitter, dry edge; good fresh beans can skip it.
Return the beans to the pan with 1.2 litres of the measured water. Bring to the boil, then turn the heat right down so the surface barely trembles. Lay a circle of baking paper on the water (it stops the beans tumbling and splitting) and simmer for 1–1½ hours. Top up with hot water from the kettle whenever the beans start to poke through.
Test a bean: it is ready when it squashes easily between your thumb and finger but still keeps its shape. Do not add any sugar before this point, as it toughens the skins and the beans will never soften properly.
Stir in the sugar in two or three goes, gently so the beans stay whole, and simmer for another 10 minutes until the liquid looks glossy and a little thicker. Add a small pinch of salt, which sharpens the sweetness. Thin with some of the remaining hot water for a looser soup, or simmer a little longer for a thicker one. Taste once it has cooled slightly, as it seems sweeter as it cools.
Meanwhile toast the mochi: lay the halves on a lined tray under a hot grill, in a dry non-stick frying pan, or in the oven at 220 °C (fan 200 °C), gas 7, for 8–12 minutes, turning once, until they puff up and brown in patches.
Put two pieces of toasted mochi in each warmed bowl, ladle the hot bean soup over and serve straight away, ideally with a cup of green tea.
Tip: tap a step to tick it off as you cook.
See also
Chef’s notes
- Mochi is very sticky and can be a choking hazard. Cut it into small pieces for children and older people, and eat it slowly.
- Shortcut: warm 400 g ready-made chunky sweet red bean paste (tsubuan) with about 400 ml water and a pinch of salt, then add the mochi.
- Without the mochi, the bean soup keeps for 4 days in the fridge or a month in the freezer. Toast the mochi just before serving.
- Variations: small glutinous-rice dumplings (shiratama dango) instead of mochi; sweet chestnuts; or serve the soup chilled in summer. A few strips of salted kelp (shio kombu) on the side make a good salty contrast.
Zenzai or shiruko?
Japan has two names for sweet azuki soup, and what each one means depends on where you are. Shiruko (or oshiruko) is a sweet bean porridge served with mochi. In western Japan, zenzai means a version with whole or roughly crushed beans, like this one; elsewhere it can mean a thicker, jam-like bean mixture, and in Okinawa zenzai is sweet beans and mochi served over shaved ice.
Because it is so sweet, shiruko is traditionally served with something sour or salty on the side, such as pickled plum (umeboshi) or salted kelp. Zenzai is a favourite way to eat up the New Year rice cakes at kagami biraki, when the ceremonial mochi is broken open, usually on 11 January.
Sources: Wikipedia: Shiruko (citing Hiromi Otani, Nipponia No. 28, Web Japan, 2004), Just One Cookbook: Zenzai (kagami biraki on 11 January).
How this recipe was developed
The old Cookeryonline page quoted a recipe from a published book, so we wrote a new one. We compared three of the most-used Japanese home-cooking versions in English; none of our usual preferred chefs has published a zenzai, so they are not listed.
- Quick first boil. Chopstick Chronicles (Shihoko Ura) and Japanese Cooking 101 both boil the beans briefly and throw the water away to remove bitterness. Just One Cookbook (Namiko Hirasawa Chen) says good modern beans can skip it, so we made it optional.
- Sugar only when the beans are soft. Just One Cookbook explains that sugar added too early toughens the skins. All three versions add it at the end.
- Less sugar. Japanese Cooking 101 uses 1½ cups of sugar to a cup of beans and Chopstick Chronicles ¾ cup (a reader there found it too sweet). We use 150 g to 200 g of beans, inside Just One Cookbook’s range, and remind you that it tastes sweeter as it cools.
- Pinch of salt and toasted kirimochi. All three finish with a little salt and toasted plain rice cakes. The safety note on sticky mochi follows Just One Cookbook’s advice to readers about serving it to young children.
Sources we compared (ratings as shown on each site on 31 October 2026):
- Just One Cookbook (Namiko Hirasawa Chen): Zenzai (Sweet Red Bean Soup with Mochi)
- Chopstick Chronicles (Shihoko Ura): Sweet Red Bean Soup (Oshiruko/Zenzai)
- Japanese Cooking 101: Zenzai (Oshiruko) Recipe
This is an original Cookeryonline recipe written in our own words. Ingredient choices and techniques are credited above; no source text has been copied.