How to Make Oshiruko, Painlessly: The “Just Add More Water” Approach

By Rika Hoffman
Updated: December 29, 2022

The sweet red bean soup I grew up with is rustic. With plump, partially-macerated beans, the oshiruko of my childhood is served not at a restaurant but at home, where nobody can be bothered to painstakingly strain the bean paste, and where a small amount can be stretched with extra water—something my mother told me, gleefully, that a kooky aunt of hers would do to accommodate unexpected guests during the holidays (this claim has not been substantiated by my grandmother, obaasan).

Arguably, some of the best foods are the simplest, oshiruko included. For what could be more comforting on a nippy winter day than thick pillows of toasted mochi floating in a bowl of nourishing sweet bean soup?

While it’s a staple Japanese New Year food, this sweet red bean soup can be enjoyed all year round. Here, we share two no-fuss oshiruko recipes—both chilled and hot—to sustain you through scorching summer days and numbingly chilly ones alike.

Two bowls of hot oshiruko, with squares of toasted mochi

What is Zenzai (Oshiruko)?

Zenzai, also referred to as oshiruko (more on this later), is a sweet Japanese red bean soup. It’s made with just a handful of ingredients: red beans, sugar, and mochi (or dango). The traditional rice cake mochi is an immensely significant staple in Japanese cuisine, particularly around the New Year holidays.  

Typically, zenzai is served as a hot porridge during the winter, around the same time as the celebratory osechi ryori (Japanese New Year cuisine), but it can also be enjoyed as hiyashi (chilled) zenzai in the warmer months. 

Is Zenzai a Dessert?

The inclusion of beans might have you incredulously wondering, “Is zenzai a dessert?” The answer is a resounding yes! Like a lot of Japanese sweets and confections, zenzai features sweet beans as the main character. However, I wouldn’t blame you for enjoying it as an anytime meal; red beans make it both filling and nutritious.

What is the Difference Between Zenzai and Oshiruko?

After doing some digging online and having conversations with my mother and obaasan (grandmother), we came to the conclusion that there’s no universal answer to the difference between zenzai vs. oshiruko. 

But while these are not clear-cut rules, different regions of Japan do tend to use different vocabulary to refer to the sweet mochi soup. 

In the Kansai region (which includes Kyoto and Osaka), it comes down to the texture of the bean paste. There, zenzai is made with tsubuan (chunky red bean paste) while oshiruko uses koshian (smooth red bean paste). 

Meanwhile, in Kanto (the geographical region that includes Tokyo and Yokohama, where my mother was born), oshiruko and zenzai seem to be differentiated by the water content of the soup. Whether made with koshian or tsubuan, oshiruko in Kanto tends to be soupier while zenzai is thicker.

However, oftentimes the term used varies depending on the preference of the individual family or restaurant, as much as the region. 

According to my mother, the spokesperson for our family in Yokohama, “Zenzai sounds more professional. More artisanal. Oshiruko is more homemade or country-style.” She assures me that obaasan shares the same view.

Their impression of zenzai is that it's more refined, likely made at a restaurant using thicker koshian (smooth bean paste). As koshian is more processed (the beans are strained through a sieve to achieve that perfectly silky texture), it is harder to achieve at home and more likely to be the labor of a professional.

The rustic oshiruko, meanwhile, tends to be soupier with visible grains of crushed beans. 

How to Make Zenzai a.k.a. Oshiruko

Chopsticks raising toasted mochi from a bowl of zenzai, Japanese sweet bean soup

Both the traditional hot oshiruko recipe and the less-orthodox chilled version that's made with shiratama dango start with anko (sweet bean paste), which is the base for many traditional Japanese sweets or wagashi

If you can find canned anko at your local Japanese or Asian grocery store, feel free to skip the “How to Make Anko” section below and continue on with the recipes. But if you don’t have access to sweet bean paste (or prefer an entirely homemade approach), it’s quite simple to make anko at home using three accessible pantry ingredients. 

How to Make Anko: The “Just Add More Water” Method

Got your beans, sugar, and salt? This anko recipe is as easy as boiling water. 

Tsubuan (Chunky Red Bean Paste) Ingredients:

  • 375g red beans
  • 275g sugar
  • 3/4 tsp salt

Method: How to Make Tsubuan (Chunky Red Bean Paste)

To soak or not to soak; there are two camps of bean-cooking. 

The argument for soaking is, of course, that the beans cook faster. But if you want to preserve the vibrant color of the beans, then we advise you not to soak them. It may take a little longer on the stovetop, but it’s mostly hands-off cooking anyway.

Rinsing red beans in a colander

Whatever camp you’re in, make sure to rinse your beans and discard any that are cracked. Transfer them to a pot with a lid that fits, and cover the beans with an inch or two of water. Boil the beans on medium heat. Scoop out any foam that develops on top of the water.

Boiling red beans

Once the beans come to a boil, turn the heat to low and simmer, checking occasionally to make sure that the water hasn’t totally evaporated (and the bottom isn’t burning!). 

After the beans are tender (about an hour) add the sugar in three batches, stirring with each addition to ensure that all the sugar is dissolved before adding the next batch. 

Pot full of cooked red beans and sugar

Grab your macerating tool of choice—we used a whisk, but a potato masher works just as well—and stir (or mash) vigorously until the beans are your desired texture, crushing some and leaving some beans whole.  

Feel free to continue reducing the mixture until thick and easy to store in a container, or you can proceed to use it in the recipes below. 

Anko Making Tips:

  • To preserve the red color of the beans, we suggest that you don’t soak the beans or drain the soaking liquid. Also, using a darker sugar like kokuto (Okinawan black sugar) can result in a richer color than light brown sugar. 
  • The less sugar you use, the more natural/lighter the color will be. Feel free to adjust the amounts of sugar to your liking. 

How to Make Hot Oshiruko: Winter Zenzai Recipe

Close-up of hot oshiruko in a bowl, with chopsticks holding up mochi

Hot Oshiruko Ingredients:

  • 2 cups anko - homemade or packaged
  • 1 cup water (or to liking)
  • 2 blocks of kirimochi
  • Optional: shibazuke pickles

Serves: 2 

Method: Hot Oshiruko Recipe

First, take your blocks of kirimochi (literally “cut mochi”) and snap them into bite-sized pieces.

Kirimochi on a small plate

Pop the kirimochi in the toaster to cook as you prepare the red bean soup. You’ll know they’re done when they have puffed up and browned. 

In a pot over medium heat, heat the anko and water. Feel free to add more water for a thinner texture, or more anko for a heartier bite. 

Ladle full of sweet red bean soup in a pot

Pour the red bean soup into a bowl and top with the mochi. 

As an optional step, include a mini side dish of shibazuke or shisonomi pickles.

Shibazuke is a type of eggplant tsukemono that originated in Kyoto, with a vibrant purple color thanks to the addition of purple shiso (a.k.a. perilla) leaves. Shisonomi, meanwhile, is a verdant green, made from shiso seeds.

Purple shibazuke and green shisonomi pickles in a dish

While it may sound strange, these pickles are a welcome palate-cleanser between bites of the rich and sweet oshiruko, adding a much-needed crunch and acidity.

Two packages of Japanese pickles

How to Make Hiyashi Shiratama Zenzai: Cold Oshiruko Recipe

Bowl of hiyashi shiratama zenzai with a scoop of matcha ice cream

Hiyashi Shiratama Zenzai Ingredients

  • 50g shiratamako 
  • Approx. 40-45g water
  • 1 cup water (or to liking)
  • 2 cups anko - homemade or packaged
  • Optional: vanilla or matcha ice cream

Serves: 2 

Method: Hiyashi Zenzai Recipe

Start by preparing the red bean soup. In a pot on medium heat, combine anko and desired amount of water to achieve your preferred consistency. It comes down to personal preference, but hiyashi zenzai tends to be more refreshing when served as a thinner soup compared to hot zenzai.  

Allow the soup to chill in the fridge while you prepare the shiratama dango.

In a bowl containing 50g of shiratamako, slowly add the water, reserving some liquid as you may not need it all. 

Shiratamako in aluminum bowl

Knead the dough until the shiratamako has absorbed all the water. In the beginning, it will look dry and crumbly, but it will come together into a smooth ball. It should be easy to handle and dry to the touch—not tacky.  

Kneading dango dough in an aluminum bowl

Separate the balls into small, bite-sized dango. 50g of shiratamako should make approximately 8-12 balls. 

Rolling dango balls by hand

In a pot of boiling water, drop in the dango. They will sink initially, but float to the surface as they cook. After all the dango have risen, cook for another 3 minutes until they're done.

Transfer the cooked dango into an ice bath to cool them down.

Boiling shiratama dango in a pot next to an ice bath

Now, retrieve your chilled anko soup and add the dango. Top with ice cream if desired. Matcha and vanilla ice cream are both great options here. 

Cold oshiruko with dango in a blue bowl

And there you have it! Two easy zenzai recipes for any season. Give it a try, and if you like the results, be sure to share your photos and tag us on Instagram.

Love Japanese sweets? Join our Intensive Wagashi and Mochi Making Course with Mai the wagashi artist, and learn how to make intricate treats out of red bean paste and mochi!

We strive to be as accurate as possible and keep up with the changing landscape of Japan's food and travel industries. If you spot any inaccuracies, please send a report.
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Rika Hoffman
Rika is a sourdough enthusiast, amateur film photographer, and pun-lover, born and raised in the suburbs of Philadelphia. A carb-based lifeform, she is always on the lookout for tasty bakeries in Tokyo.
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