Yaki Imo (Japanese Roasted Sweet Potatoes)
Japanese winter street food: whole sweet potatoes roasted low and slow until the skin wrinkles and the flesh turns deep golden, jammy, and sweet enough to eat as dessert.
Servings 4 servings
Ingredients
For the Yaki Imo
- 4 Japanese sweet potatoes 10 to 12 ounces each, beni haruka, beni azuma, or silk sweet
- flaky salt to serve, optional
- unsalted butter to serve, optional and not traditional
Instructions
Roast the Sweet Potatoes
- Scrub the sweet potatoes under cold water and dry them completely. Leave the skins on, do not oil them, and do not prick them.
- Set the potatoes on a foil-lined sheet pan with space around each one, place the pan in a COLD oven, then set the oven to 300F. Starting cold gives a slower climb through the temperature band where starch converts to sugar.
- Roast 80 to 120 minutes depending on size, about 90 minutes for a 10 ounce potato. Around the hour mark dark syrup will bubble from the ends and splits in the skin.
- Test for doneness: a skewer slides through with no resistance, the potato gives softly along its whole length when squeezed through a towel, and the skin has wrinkled and loosened.
- Rest 10 minutes on the pan, then split each potato lengthwise and eat the flesh straight from the skin, plain or with flaky salt and butter.
Notes
- Low oven, long roast: the enzyme that turns starch into sugar works between about 150F and 170F inside the potato, so a hot oven gives you a starchy potato instead of a sweet one.
- Roast bare, not in foil: bare skin wrinkles and blisters and the flesh concentrates; foil steams it soft and mild.
- Buy them early: a week in a cool dark place makes them sweeter. Never refrigerate raw sweet potatoes.
- Cold yaki imo: chilled overnight the flesh firms into something close to a dense custard, and it is a real Japanese preference.
- Storage: 4 days refrigerated wrapped whole, 2 months frozen.