Daifuku (Soft Mochi Wrapped Around Sweet Red Bean Paste)

Name: Daifuku (Soft Mochi Wrapped Around Sweet Red Bean Paste)
Prep time: 40 min
Cook time: 5 min
Total time: 45 min
Yield: 8 servings
Cuisine: Japanese
Ingredients: 240 g sweet red bean paste; 100 g shiratamako; 40 g sugar; 160 ml water; 60 g potato starch; 8 strawberries; 60 g simmered black soybeans; 5 g dried mugwort powder

A Japanese sweet: red bean paste wrapped in a thin skin of glutinous rice. The reason mochi stretches is amylose. Short-grain rice starch is about 17 per cent amylose, the straight molecule that recrystallises quickly; glutinous rice has almost none, so mochi stretches and is still soft the next morning.

Ingredients

8servings

The filling (makes 8)
sweet red bean paste · koshian or tsubuan; shop-bought is fine240 g
The mochi skin (gyuhi)
shiratamako · glutinous rice flour; mochiko works too100 g
sugar · it holds water as much as it sweetens; leave it out and the skin is hard by the next day40 g
water160 ml
For dusting
potato starch · katakuriko; cornflour tastes chalky60 g
Variations
strawberries · for ichigo daifuku; small and firm8
simmered black soybeans · for mame daifuku, folded into the dough60 g
dried mugwort powder · for yomogi daifuku5 g

Steps

Roll the bean paste into eight 30g balls and chill them firm. The filling has to be cold and the skin hot; the other way round and it cannot be wrapped at all.
⏲ 30 min
In a heatproof bowl, whisk the shiratamako and sugar with the water added a little at a time until there are no lumps. Shiratamako is coarsely granular and will not disperse if all the water goes in at once.
⏲ 5 min
Cover and microwave 2 minutes. Beat it hard with a wet spatula, right down to the bottom. The edges cooked and the middle still white is normal at this stage.
⏲ 2 min
Microwave 1 minute more and beat again. It is ready when the whole mass is translucent and comes away from the bowl in one piece. Underdone it tastes of raw flour; overdone it turns tough.
⏲ 1 min
Give it another 30 seconds if it needs it. With a steamer, steam the same mixture 20 minutes over hard steam and then pound it.
⏲ 30 sec
Turn it out onto a tray dusted generously with potato starch and dust the top as well. The dough is hot — work with starch on your hands.
⏲ 1 min
Cut it into eight and press each piece into a disc that is thin at the rim and thick in the middle, because the base ends up thickest once it is wrapped.
⏲ 5 min
Set a cold ball of paste on each, draw the dough up, pinch it shut and turn the seam underneath. Brush the loose starch off — left on, it tastes chalky.
⏲ 5 min
Eat them the same day. Do not refrigerate them — 0-4°C is where rice starch firms fastest.

Variations

Mame daifuku: simmered black soybeans folded into the dough, salty enough to cut the sweetness.
Yomogi daifuku: mugwort in the dough, the same ingredient that makes green songpyeon.
Shio daifuku: salt in the dough rather than sugar alone.
Yukimi daifuku: the modern one with ice cream inside. It does not go rock hard in a freezer because there is almost no amylose and the sugar is holding the water.
Korean chapssaltteok is effectively the same sweet; rolled in soybean flour it becomes injeolmi.

More detail and the reasons why (1)

Ichigo daifuku: wrap the strawberry completely in bean paste first, then in the mochi. The order matters — water coming out of the fruit dissolves a skin it touches directly, and the paste works as a barrier.

Tips

Why not the fridge: 0-4°C is the band where rice starch firms fastest. Mochi is not exempt, only much slower.
Potato starch is a release agent, not an ingredient. Use plenty and brush the surplus off at the end. Cornflour leaves a chalky film.

More detail and the reasons why (6)

One number is the whole difference: amylose. Rice starch is a mixture of straight-chain amylose and heavily branched amylopectin. Ordinary short-grain rice is around 17 per cent amylose; glutinous rice is effectively zero. The molecule that recrystallises as it cools — which is what staling is — is the straight one. Branched amylopectin cannot stack against its neighbours, so it firms up far more slowly. The stretch has the same cause.
The same number explains other rice doughs. Dango made with glutinous flour alone becomes far stretchier, like mochi, and a songpyeon dough made with it slackens and stales differently.
The sugar is not only for sweetness. Of sugar's jobs (what sugar does), moisture retention is close to structural here. Halve the sugar and the result is not less sweet, it is hard by the next day.
Fufu: the same action, a different outcome. Its gelatinised starch is pliable while hot, and as it cools it retrogrades and no amount of pounding will make it elastic, because cassava starch has amylose in it. Mochi is still stretchy a day later.
Other dishes work with staling or against it. Lamington requires a staled crumb, arancini needs rice that has gone cold and tacky, Spam musubi has to be pressed before the rice firms, and shokupan slows staling with a pre-gelatinised starch paste. Daifuku starts from a material that barely stales at all.
The filling has to be dry. Water in the filling is what bursts a wrapper (wrapping and sealing), and that applies here too — bean paste has already been cooked down, which is why it causes no trouble, and a strawberry gets a coat of paste for the same reason.