Jump to Recipe
Karukan is a steamed Japanese yam cake, similar in technique to a steamed Newfoundland figgy duff, made by whisking grated nagaimo into egg whites and sugar, then folding in flour before steaming until the crumb turns pale and spongy.
I first tried it in a tea shop in Kagoshima, served in a thin slice next to a cup of green tea. No frosting, no filling, just a soft, almost marshmallow-like bite from the yam.
The grated mountain yam is what gives karukan its bounce. It’s slippery and a little intimidating to grate at first, but once it’s whisked into the eggs, it disappears into the batter and leaves behind a spring you don’t get from flour alone.
This version skips the fancy kokuto syrup some bakeries use and sticks to pantry sugar, so it’s easy to make on a random Tuesday. Steam it, let it cool, slice thin.
Why You’ll Love This Recipe
- No butter, no oil, just yam and eggs for lift
- Steaming keeps it moist for days without drying out
- Only five ingredients, most already in your pantry
- A quiet, unusual bake that isn’t sweet or heavy
Ingredient Notes
- Nagaimo (Japanese mountain yam): Use fresh nagaimo, peeled and grated right before mixing since it browns fast. Yamaimo works too but is stickier, so cut back the water by half.
- Egg whites: Save the yolks for custard or fried rice. Room temperature whites whisk up foamier than cold ones.
- Granulated sugar: Swap half for kokuto (Okinawan brown sugar) if you can find it, for a deeper, slightly caramel note.
- Cake flour: Gives a lighter crumb than all-purpose. Sift it with the baking powder so it folds in without lumps.
- Baking powder: A small insurance policy for rise since this batter isn’t whipped into a stiff meringue like sponge cake.
Karukan: A Soft Steamed Japanese Mountain Yam Cake
Ingredients
Method
- Peel the nagaimo and grate it finely into a bowl. Stir in the water right away to keep it from browning.
- Fill a 30 cm / 12-inch steamer pot with a few inches of water and bring it to a rolling boil. Line an 18 cm / 7-inch round cake pan with parchment and lightly grease the sides.
- In a large bowl, whisk the egg whites with the salt until foamy, about 1 minute. Don't take them to stiff peaks.
- Add the sugar in two additions, whisking after each, until the mixture is pale and slightly thickened, about 3 minutes.
- Fold the grated nagaimo into the egg mixture until evenly combined.
- Sift the flour and baking powder over the batter in two additions, folding gently each time until no dry streaks remain. The batter should be thick but still pourable.
- Pour the batter into the prepared cake pan and tap it on the counter twice to release large air bubbles.
- Cover the pan loosely with foil to keep condensation from dripping onto the top. Place it in the steamer basket.
- Steam over a rolling boil for 35 to 40 minutes, until a skewer inserted in the center comes out clean and the top springs back when pressed.
- Remove the pan carefully and let it cool in the pan for 10 minutes. Turn the cake out onto a rack and cool completely, about 15 minutes, before slicing thin.
Notes
- Grate nagaimo just before mixing, it browns within minutes.
- Cover the pan with foil to block dripping condensation.
- Whisk egg whites to foamy stage only, not stiff peaks.
- Cool completely in the pan before slicing thin.
Tips for Success
- Grate the nagaimo right before mixing since it oxidizes and turns gray within minutes of sitting out.
- Whisk the egg whites until just foamy, not stiff peaks, or the finished cake turns rubbery.
- Cover the cake pan with foil before steaming so condensation doesn’t drip and leave soggy dents on top.
- Keep the steamer water at a steady rolling boil the whole time, the same approach used for a Sussex pond pudding, for an even, steady rise.
- Cool the cake completely in the pan before slicing or it will stick to the knife and tear.
Variations
- Swap half the sugar for kokuto (Okinawan brown sugar) for a deeper caramel note and darker color.
- Add a few drops of red food coloring to half the batter for the classic pink-and-white marbled look.
- Stir in a tablespoon of grated ginger for a warmer, spicier cake to serve with hot green tea.
Storage and Reheating
Karukan keeps well at room temperature, covered, for 1 to 2 days, or in the fridge for 4 to 5 days wrapped tightly so it doesn’t dry out.
To warm it back up, re-steam slices for 3 to 4 minutes, or microwave a slice covered with a damp paper towel for 15 to 20 seconds. Both bring the spongy texture back without drying the edges.
Freeze whole slices wrapped individually for up to 1 month. Thaw at room temperature for about an hour before serving.
Serving Suggestions
Karukan is usually eaten plain, sliced thin, with a cup of green tea or hojicha on the side, much like a slice of Tottenham cake pairs with an afternoon tea. The mild sweetness doesn’t need anything else.
If you want more of an afternoon-snack spread, set it out with a few pieces of yokan or a bowl of edamame for contrast in texture.
A light dusting of kinako (roasted soybean flour) on top adds a nutty note if you want to dress it up for guests.
FAQ
Why did my karukan turn out dense and rubbery instead of spongy?
This usually means the egg whites were whisked to stiff peaks or the flour got overmixed once folded in. Karukan wants foamy, not stiff, egg whites, and a gentle fold that keeps some air in the batter. Overworking the flour builds gluten, which turns the crumb tight and chewy instead of light.
Can I use yamaimo instead of nagaimo for karukan?
Yes, yamaimo works but it’s noticeably stickier and starchier than nagaimo. Cut the added water by about half and expect a slightly denser, more elastic crumb. Nagaimo is milder and looser, which is why most karukan recipes call for it specifically.
How do I store karukan and can I freeze it?
Store karukan covered at room temperature for 1 to 2 days or in the fridge for 4 to 5 days. It freezes well too, wrapped in individual slices for up to 1 month, then thawed at room temperature for about an hour before eating.
What goes well with karukan Japanese yam cake?
Green tea or hojicha are the classic pairing since the cake itself is mild and only lightly sweet. It also works alongside other Japanese sweets like yokan or mochi on a tea-time plate. Skip heavy toppings, they compete with the delicate crumb instead of complementing it.
Is karukan gluten free?
No, this traditional version uses cake flour, so it contains gluten. You can try swapping in a 1:1 gluten-free baking blend, but the crumb will be denser and less bouncy since wheat flour’s structure is part of what holds the whipped batter together.
What’s the difference between karukan and castella cake?
Karukan is steamed and made with grated mountain yam for its spongy texture, while castella is baked and relies on whipped whole eggs and honey for a denser, moist crumb. Karukan is paler, lighter, and less sweet than castella overall.
More from the kitchen
- our Easy Soft One-Bowl Banana Snack Cake with Cinnamon
- the Soft One-Bowl Cinnamon Yogurt Cake with Sugar Swirl
