When I was small, the fall and winter seasons were extremely exciting because the sweet potato man would come on his truck. You can hear him coming around the block singing "Ishiyaki imo~" (literally meaning stone-cooked sweet potatoes). No music, just him singing through the megaphone for the whole neighborhood to hear.
On the back of his small white truck, he'd have a bunch of sweet potatoes cooking on hot stones. Thinking back, the sweet potatoes were always a hit or miss. Sometimes you get one that's moist and sweet, but more often than not, you get one that's dry and crumbly. You never knew what you were getting until you broke it open.
It was still a treat to get the man to hand you a piping hot sweet potato in the cold weather.
I still hear the sweet potato man in the evenings driving around our town and feel a bit nostalgic, but I don't go rushing out of my house like I did when I was a kid. I've figured out how to roast them at home, and they always turn out perfectly. The sweet potato man's got nothing on me.
Japanese sweet potatoes vs North American sweet potatoes
Japanese sweet potatoes are harder and starchier than North American sweet potatoes, so my slow roasting process works well.
The Japanese sweet potatoes generally have a reddish-purple skin and a creamy white center. My favorite kind of sweet potato is Annoh-imo (安納芋). They're known to be sweeter and moister (and also pricier) than other sweet potatoes, but this method works with all Japanese sweet potatoes.
How to slow roast Japanese sweet potatoes
Wash the sweet potatoes with water to get all the dirt off. You might be tempted to peel the skin off or cut the ends off, but don't do it. All of the skin needs to stay on to keep the moisture in.
If you peel or chop them, they'll dry out in the oven. You can peel and chop after they come out of the oven. I like to eat them skin on so I make sure to scrub them with a sponge or brush.
Wrap each sweet potato in aluminum foil and place them on a baking sheet lined with parchment paper. Place in a cold oven and bake at 320°F/160°C for about 90 minutes. It's important you don't preheat the oven, so they gradually bake and develop a sweet, candy-like flavor.
You need to line the baking sheet because once these bake up, the sweet juice starts oozing out and you don't want it to caramelize on your baking sheet. The less clean-up I have to do, the faster I get to eat.
The caramelized bits are basically sweet potato flavored candy, so definitely peel them off and eat them.
I took them out of the oven at 90 minutes, but if your potatoes are bigger leave them in for another 20 minutes or so. It's a bit of a wait, but the patience will pay off, I swear!
Once they're cool enough to handle, peel off the aluminum. You might find that your sweet potato is wet but no worries, it just means it's extra moist.
Just look at that. Super moist, perfectly cooked sweet potatoes. The longer you bake them, the sweeter they become. They're so sweet on their own, there's no need for any butter or sugar.
They are apparently high in vitamin A, vitamin C, B vitamins, potassium, fiber, and manganese. Who'd a thunk they were so nutritious?
Recipes to try!
Oven-Baked Japanese Sweet Potatoes
- Japanese sweet potato
- Wash the sweet potatoes and wrap them individually in aluminum foil. Don't peel or cut the sweet potatoes. Place them on a parchment paper lined baking sheet.
- Put the baking sheet in a cold oven and bake at 320°F/160°C for anywhere from 90 to 120 minutes. Baking times will vary depending on the size of the sweet potato. Start with 90 minutes and feel for doneness. If you see juice seeping out and getting caramelized on the parchment, or if the sweet potatoes feel soft to the touch, they're done.