Oshiruko is a hot, sweet azuki-bean soup, served with a piece of grilled mochi or with soft shiratama rice-flour dumplings floating in it. The beans are simmered with sugar to a sweet soup, either smooth (from sieved koshian) or thick with whole beans (tsubuan), and a pinch of salt is added to round out the sweetness. It is eaten warm from a bowl, most of all in winter and at New Year, and is often accompanied by a small salty or sour side such as pickled plum or salted kelp to cut the sweetness. A nearly identical dish is called zenzai, and which name applies depends on the region.
Sweet azuki soups of this kind are old and pan-Japanese, and the exact origin is unrecorded; what is well documented is a regional split in naming between eastern and western Japan. In Kanto (the Tokyo region), oshiruko is the umbrella term for any sweet red-bean soup, whether made smooth or with whole beans, while zenzai means a thick paste with little or no liquid, eaten with mochi. In Kansai (the Osaka–Kyoto region), the two names instead mark texture: oshiruko is the smooth, sieved (koshian) soup, and zenzai is the chunky soup made with whole beans (tsubuan). The dish is strongly tied to winter and to New Year, when leftover kagami-mochi is broken up and cooked in it.
The soup is hot, sweet and deeply red-brown, with the earthy, husky flavour of azuki under the sugar; the salt keeps the sweetness from cloying. A smooth version is velvety and even on the tongue; a chunky one carries soft, mealy whole beans you can feel break. The mochi is the centre of the bowl — grilled, it arrives blistered and faintly smoky outside and molten, stretching and chewy within, soaking up the soup. The salty pickle on the side resets the palate between spoonfuls. Eaten too cool, the soup turns pasty and the mochi stiff.
Two things make the bowl. First the soup: azuki are boiled, the first bitter water discarded, then simmered soft and cooked with sugar; sugar concentration both sweetens and thickens, and a pinch of salt sharpens the perceived sweetness by contrast rather than adding saltiness. Sieving the cooked beans removes the husks for a smooth koshian soup; leaving them whole gives the chunky tsubuan style. Second the mochi: glutinous rice is almost pure amylopectin, so when grilled its starch network softens and turns stretchy and molten inside while the surface dries, browns and blisters, giving the chew and the toasted note that anchor the dish.
Variations
The clearest variation is the regional naming itself — oshiruko versus zenzai, smooth versus chunky, soupy versus thick — which shifts between Kanto and Kansai. The garnish also varies: a grilled square of mochi, or soft boiled shiratama dumplings, or in some places roasted chestnuts or boiled chestnut. In Okinawa, 'zenzai' is a quite different thing — a cold dessert of sweet beans over shaved ice. A close cousin is awa-zenzai, made with millet, and the same sweet azuki soup is the base note that runs through much of wagashi.
On the Palate
Where Oshiruko sits in the Japanese flavor cloud
Ingredients
Serves 4How it's made
7 steps · 1 hour
- 110 min
Rinse the azuki beans, cover with water, bring to a boil, then drain off the first bitter water.
Watch outBoil the azuki once and pour off the first water — that first bitter water carries the harshness; keep it and the soup tastes astringent.
- 270 min
Add fresh water and simmer the beans gently until very soft, topping up the water as needed.
- 320 min
Stir in the sugar in stages and cook to a sweet soup; for koshian, sieve out the husks, for tsubuan leave the beans whole.
- 45 min
Add a pinch of salt to balance the sweetness and loosen with a little hot water to the desired consistency.
Watch outAdd a pinch of salt to the sweet soup — it sharpens the perceived sweetness by contrast without making it salty.
- 58 min
Grill the mochi until puffed and browned, or boil shiratama dumplings until they float.
Watch outGrill the mochi until it puffs and browns and blisters — the surface dries and chars while the inside turns stretchy and molten.
- 63 min
Place the mochi or dumplings in bowls and ladle the hot bean soup over.
- 72 min
Serve at once with a small salty or sour side such as umeboshi or salted kelp.
Archive tool suggestions — not reviewed
These legacy suggestions have not been evidence-reviewed and are not presented as required tools.
