Kagoshima Yam Cake (軽羹, Karukan)

Ingredients

Equipment Needed

• •Oroshigane (Japanese grater), or a fine ceramic grater
• •Suribachi and surikogi, or a wide bowl and balloon whisk
• •15cm square nagashi-kan mold, or a small parchment-lined heatproof cake pan
• •Steamer with a cloth-wrapped lid

Instructions

1. 1

   Prepare the mold

   Line a 15cm square nagashi-kan, a small heatproof cake pan, or eight shallow cups with parchment. Set up a steamer with plenty of water and wrap the lid in a clean cloth, tying the corners up away from the heat. Bring the water to a lively boil before the batter is finished; once rice flour goes in, you want the cake cooking at once so the trapped air doesn't sit and fade.

   The cloth catches drips from the lid. Water falling onto the surface makes gummy marks on a cake whose beauty is its plain white face.
2. 2

   Grate the yam

   Peel the yam just before using. Wear gloves if yamaimo irritates your skin, which it often does, not politely. Grate it on an oroshigane, a Japanese grater, or a fine ceramic grater until it becomes a smooth white paste that clings to the spoon and stretches in threads. If it slides loosely like a puree, you are probably using nagaimo, so keep the water toward 60ml.

   That sticky body is the leavening here. A blender makes the yam too loose and robs the cake of the lift you were trying to keep.
3. 3

   Beat in sugar

   Move the grated yam to a suribachi, a Japanese grinding bowl, or a wide mixing bowl. Beat it with a surikogi or balloon whisk for 3 minutes, until glossy and slightly paler. Add the sugar in three additions, beating well after each one until the grit disappears and the paste looks smooth again.

   Sugar loosens the yam while helping it hold the air you are beating in. Dump it in all at once and the paste turns lumpy and heavy.
4. 4

   Loosen with water

   Add the cold water a spoonful at a time, beating after each addition. Stop when the mixture falls from the whisk in a slow, thick ribbon. Use the full 90ml for dense jinenjo or yamatoimo; with watery nagaimo, stop earlier. The batter should be light, not soupy.

   Water helps the rice flour hydrate, but too much makes the crumb damp and low. Add it slowly and let the yam tell you when it has had enough.
5. 5

   Fold rice flour

   Sift or rain the karukan-ko into the yam mixture in three additions, folding gently but thoroughly after each one. Scrape the bottom of the bowl, where dry flour likes to hide. Let the batter rest for 10 minutes, then fold once more. It should be thick, glossy, and able to hold a shallow line for a moment before closing.

   Karukan-ko is non-glutinous rice flour. Mochiko is glutinous rice flour and gives chew, not the tender snowy crumb this cake asks for.
6. 6

   Steam the cake

   Spoon the batter into the prepared mold, about 2.5cm deep, and smooth the top with a wet spatula. Tap the mold once on the counter, only once, to settle large gaps without knocking out the fine air. Set it in the steamer, cover, and steam over strong steady heat for 22 to 25 minutes, or 14 to 16 minutes for small cups. It is done when the top is matte, springs back lightly, and a skewer comes out clean with no wet paste.

   Strong steady heat sets the rice starch around the yam's trapped air. A timid steamer lets the cake sag before it sets.
7. 7

   Cool and cut

   Lift the mold out and let the cake cool for 15 to 20 minutes. Unmold it, peel away the parchment, and cut it into small rectangles with a damp knife, wiping the blade between cuts. Cooling gives the rice starch time to settle; cut too soon and the face tears instead of showing those tiny even pores.

8. 8

   Serve with tea

   Serve the karukan the same day with sencha or matcha, in small pieces with space around them. Three pieces on a plate looks more generous than a crowd of them. If you have made it ahead, wrap it airtight once fully cool and refresh it briefly in the steamer before serving.

Chef Tips

• •Choose yamaimo that feels heavy and firm, with no soft spots and a fresh cut end. Late autumn into winter is its shun. If you can buy yamatoimo or jinenjo, do; if nagaimo is all you have, use less water and expect a gentler rise.
• •Karukan-ko gives the closest crumb because it is made for this sweet. Jōshinko is the working stand-in. Mochiko is a different flour and will pull the cake toward mochi, which is not this dish.
• •Beat the yam by hand if you can. The old suribachi does two jobs at once: it smooths the yam and works air into its sticky body. A bowl and whisk are honest enough; a blender is too rough for the texture we want.
• •Don't add baking powder or whipped egg white for this plain karukan. They change the character of the sweet. If the cake is dense, look first at the yam's stickiness, the water amount, and whether the steamer was fully hot.
• •Plain karukan is not filled. The red bean version is karukan manjū, a close relative and a good one, but a different sweet. Let this white cake stand on its own.

Advance Preparation

• •Measure the sugar and rice flour and line the mold several hours ahead. Grate the yam only just before mixing, because it darkens and loses some lift as it sits.
• •Karukan can be made one day ahead. Cool it completely, wrap it airtight, and refrigerate. Refresh it in the steamer for 3 to 4 minutes, then let it settle to warm or room temperature before serving.
• •For longer storage, freeze individual pieces tightly wrapped for up to one month. Thaw while still wrapped, then refresh briefly in the steamer so the rice flour softens again.

Frequently Asked Questions

Nutrition Information

1 serving (about 72g)