I love Japanese sweet potatoes (also called Japanese Yam). They are less watery compared to “American” sweet potatoes and sweeter in my opinion. My favorite way of eating them is baking. We called them yakiimo (焼き芋) in Japanese. When I was growing up in Japan, baked sweet potatoes were sold by a guy hauling a cart. There is an oven in a cart which bakes sweet potatoes. Stones are put in the oven to heat sweet potatoes. It’s kind of hard explain how it works but this stone-baked method makes sweet potatoes so much sweeter and tastier.
I did some research to recreate sweet potatoes baked with stones. They keys seem to be (1) sweet potatoes should be dry when they are baked and (2) they should be baked at a low temperature for a long time. I will share my method step by step. A short version of the recipe is also available at the bottom of this blog post.
- Wash sweet potatoes the night before and dry them thoroughly. Pick sweet potatoes with dark reddish skin color.
2. Preheat oven at 300 degrees F (150 degrees C). You can skip this. Sometimes I don’t preheat the oven.
3. Wrap sweet potatoes with dried paper towel then with aluminum foil. I use the shiny side inside. Paper towel will absorb moisture while basking and keeps sweet potatoes dried.
4. Place the foiled sweet potatoes on a baking sheet. The baking sheet transfers more heat and helps cooks faster (although this baking method takes a long time). I usually bake as many sweet potatoes which fit on a baking sheet (8 to 10 depending on the size).
5. Baked them until they become very soft. The longer you bake, the sweeter they become. With my electronic convection oven, it usually takes 2 1/2 to 3 hours. Yes, it takes that long! When I’m in a hurry, I bake them at a higher temperature (like 350 degrees F) but it tastes better when I bake them at 300 degrees F. Baked Japanese sweet potatoes should be golden inside and kind of fluffy. It takes a long time to bake them but you can forget about them once they are in the oven. I usually put them in the oven before I start cleaning my place and doing laundry. When I’m done with house chores, perfectly baked sweet potatoes are waiting for me 🙂
Baked sweet potatoes are stored well in the freezer. After they become completely cool, I usually wrap them in the aluminum foil that I bake them with and put them in a plastic bag to store in the freezer.
- Japanese sweet potatoes (yam) - as many as you like!
- Wash sweet potatoes the night before and dry them thoroughly.
- Preheat oven at 300 degrees F.
- Wrap sweet potatoes with dried paper towel then with aluminum foil.
- Place the foiled sweet potatoes on a baking sheet.
- Baked them until they become very soft.
Christine Laben says
Omg! I just tried this method and hands down this is the best method to make japanese sweet potatoes! Although this method takes time, the outcome of the sweet potatoes is worth it! So sweet and fluffy!!! Thank you for sharing this method! Now everytime I make my japanese sweet potatoes, this method will be used! 🙂
admin says
Thank you for your comment. Yes, it takes time but it’s worth it! 🙂
Emily says
These are SO good! I’m so happy. Thank you for sharing this recipe.
What do you think is the best way to reheat from the freezer?
Thanks ☺️☺️
admin says
Thank you for your comment. I usually move it from the freezer to the refrigerator overnight. When it is defrosted, I put it in a toaster oven (covered with aluminum foil) to reheat it! 🙂
Kris says
Hi. I’m new to making these and want to try your cooking method. Do you season the sweet potatoes with anything? Or do you usually serve them as-is? Thanks.
admin says
Hi, I just eat them as is. They are very sweet and tasty just as is. 🙂
Haley says
Everyone should try this recipe! It’s golden 🙂
admin says
🙂
Dr. Priscilla says
Great !
We need more Asian recipes easy to do with calorie, fat and salt content
admin says
Thank you! 🙂
Stephanie says
Thank you for posting this! I made this recipe two days ago and shared with my (Japanese) Mother. I was trying to recreate the flavor of the sweet potato carts.
I ended up using Korean sweet potato, which are similar, and they had the same fluffy texture.
FYI I was doing other tasks around the house and ended up leaving potatoes in for 3.5 hours at 300*. They came out fine, but that would be the longest I would stretch the cook time. I liked the fact I could “set it and forget it”
admin says
Thank you! I baked Japanese sweet potatoes yesterday. It took 3.5 hours too!
H says
Yes! This method = soft, moist, fluffy Japanese sweet potatoes. We don’t use aluminum foil anymore, so I just rubbed olive oil and sea salt into the skin, and left them for a couple hours at 300 F. Delicious, sweet, and filling. Amazing as is … and especially with slices of salty butter and a cold citrus-y drink on the side.
admin says
🙂
Libby says
Left in the oven for an extra 30 minutes. When they came out, drizzled EVOO on top with paprika and sea salt. Amazing.
admin says
Sounds good!
Leo says
In Japan we followed your recipe with one change.
We lived in what I described as a Japanese log cabin. Dark logs and tan cement exterior walls with a pitched traditional red tile roof.
But those houses have no interior built-in heatibg systems. So you have to use electric or kerosene room heaters.
We wrapped our washed and oiled sweet potatoes in tinfoil and then cooked them on top of the kerosene heater. We had a designated potato turner.
The closer to lunch the better they smelled.
I like mine with butter, salt and pepper and instead of sour cream I use Kewpie Japanese mayonnaise as a condiment.
Delishious!
admin says
Wow! Interesting!
Thank you!
Sarah says
I will try to find the Japanese sweet potato but if I can’t, will American sweet potatoes work?
admin says
Hi Sarah,
I apologize for my late reply. I don’t think American sweet potatoes will work as well as Japanese ones but you may want to try it. The water content in Japanese sweet potatoes is less so this method works well. If you try it with American sweet potatoes, let me know how it goes!
Thank you,
Mana says
I tried this method and it was amazing, but when I tried it again all the potatoes were dry. Even if I left them in longer they still stayed dry. Is there anything I can do for them to always be super moist and custardy ?
Lori says
I just made these yesterday–I’ve been making these yams for a while, but I followed your recipe and they came out beautifully! So soft and delicate inside, and of course they’re sweet. Thank you, I’m going to check out your other recipes too!
Julian Lee says
This method for baking sweet potatoes is amazing! I’ve always loved sweet potatoes, so a bit of a longer wait is a small price to price to pay to bring it to perfection. I’ll go out of my way to bake a batch of these on a bad day and it’s just perfect. Every bite is like a soft, pillowy hug that’s as sweet as can be. Thank you for sharing!
Brian says
Does anyone know why the cooked Japaneses sweet potatos have a green discolored appearance after cutting them
sometimes?
admin says
Hi Brian,
When you see a green discolored appearance, it’s usually still edible but has a weird bitter taste. It is sort of going bad. I would not eat the discolored part or the entire Japanese sweet potato with any discoloration. I’m sorry for my late reply.
Jess M says
Thank you so so much for this recipe.
It’s been such a big help for me in cooking Yakiimo.
They always turn out so delicious!
admin says
Thank you for your comment! I hope you enjoy making yakiimo!