I’m in love with baked sweet potatoes, known as Yakiimo in Japanese. They are literally very sweet. I wonder how it’s possible to contain that sweetness in natural food. With buttery and creamy texture, it’s truly decent winter dessert. Besides, it has health benefits featuring a lot of vitamins, dietary fiber and minerals. The white flesh in the purple skin becomes a shiny golden hue when baked.
I’m thrilled to tell you about my journey to the sweetest baked Japanese sweet potato “recipe”.
STEP 1: choose the best sweet potato
The best sweet potato means the sweet potato with high sugar content. Here are some tips to get a real sweet, sweet potato.
- Buy the sweet potato in the best time of year, November to January.
- Choose the branded sweet potato than non-brand.
- Look at the edge of a sweet potato and get the one syrup comes out.
My top 5 sweet potato brands, listed in the descending order of their sweetness.
- Toroama mitsu imo (とろあま蜜芋)
- Tomino kawagoe imo (富の川越芋)
- An non imo (安納芋)
- Beni haruka (紅はるか)
- Silk sweet (シルクスイート)
STEP 2: Store the sweet potato in a right place
Once you get the looks delicious sweet potato, next important thing is how to store it. But the best way to store is nothing different from other tuber. Firstly, remove the sweet potatoes from the package and wrap them in paper without washing. Then store in a cool and dark place with good ventilation. In the ideal room temperature 10 to 15 C (50 to 55 F) It will last one month. If the room temperature is higher than that, keep in a fridge and consume within a week. Make sure not to put in a freezer unless it cooked.
STEP 3: Bake the sweet potato in the best way
How to bake delicious sweet potato become a topic on media as winter gets closer in Japan. But their tips are various so I just followed curious tips one by one. Then I found my ultimate recipe in the end.
- Soak sweet potatoes in salt water overnight, then bake at 70 C (167 F) for 45 minutes.
This recipe was on the popular morning TV program, introducing from a sweet potato farmer. She said, 1 tablespoon of salt brings out the sweetness of sweet potato. And I knew that many web sites specify that sugar content increases when a digestive enzyme called beta-amylase contained in sweet potatoes is heated at a low temperature of around 70 C. So I gave it a try.
Against my expectation, obviously, those which did not in the salt water was sweeter. Besides, the texture was a little dry as it may be the temperature was too low.
- With or without aluminum foil
Generally there are 2 types of baked sweet potato recipe, with or without aluminum foil. I tried both under the same condition.
It is a matter of taste. If you are looking for sweetness and crispy skin like me, you shouldn’t wrap them up. However wrapped in an aluminum foil sheet was clearly moister than unwrapped.
- Bake at 160 C (320 F) for 90 minutes.
This is the most popular recipe of temperature and baking time rank high on search engines in Japanese. Finally, I tried the standard way.
It was tasty. But I would say, I expected more crispy on the outside. And I thought that longer baking time is necessary to get fully creamy texture on the inside.
My conclusion is
- No salt
- No aluminum foil
- The temperature should be higher than 160 C
- The baking time should be longer than 90 minutes
Based on the results, I figured out the recipe below.
- Bake at 190 C (374 F) for 90 minutes, then leave in the oven door closed for 60 minutes.
The recipe resulted in a mighty hit! This was exactly what I’d been looking for. It worked well to make crispy on the outside and creamy on the inside! It was the sweetest baked sweet potato ever. As you can see on the photograph, syrup coming out from the side. A part between skin and inside was somehow caramelized. My husband said this is the one and don’t change the recipe anymore. It was indescribably delicious.
Thank you for reading my blog post. This is how this journey came to the end. I hope you find Japanese sweet potatoes and try this out the recipe!
If you like to try other Japanese sweet potato recipe, check out my Vegan No bake Sweet Potato Pudding and Crispy Sweet Potato Spring Rolls with Pastry Cream Dip.
Referenced recipes are here and here in Japanese.
How to make the Perfect Baked Japanese Sweet Potato
- 3-4 whole Japanese sweet potao
- Wash the potatoes. You don't need to dry them up.
- Poke each potato a couple of times with a fork. Be careful not to hurt your hands.
- Place the potatoes directly onto a oven rack.
- Bake the potatoes at 190C (374F) for 1 hour and 30 minutes. Then leave them in the oven door closed for 1 hour.
Note: The recipe was updated in May 2021.
Don’t poke holes all over the sweet potato. Too many holes allows too much moisture to escape and results in a dry potato. Just poke 2 or 3 times with a fork on one side and then the opposite side of the potato
Thank you for your feedback!
Hi, may I know how these sweet potatoes can be stored in the fridge and how to reheat them the next day please? Thank you!
Hi, you can wrap the baked sweet potato with plastic wrap and store it in the refrigerator. I use the microwave to warm it up. If you use the oven, wrap it with aluminum foil and heat it at 180°C(356°F) for about 10 minutes or more.
Hi! I just got some Japanese sweet potatoes and broiled it this morning for 20 minutes, then flipped and left in for another 30 minutes. It was good! I will have to try this way next time. Sorry if this is a dumb question, do you eat the skin as well? You can just bite into the whole thing?
Hi, Thank you for visiting my site! I like to eat a whole sweet potato including skin!
This worked perfectly! I have been roasting sweet potatoes if various types in the oven or toaster oven at 400F for 60-75min but was not always happy with the results. My mom had advised me to poke holes, but that tended to result in dry sweet potatoes, so I looked at recipes online and stopped poking holes plus stopped using foil. I saw someone who commented here had an explosion, but that has never happened to me. I am going to use 375F for 60-90min plus the 60min stay in the oven with it off from now on! So soft and moist inside that my kids love it. I love the carmelized outside and chewy skin too. Yum.
Thank you for letting me know your feedback! I’m very happy to hear that you and your kids enjoyed the sweet potatoes!
I have ceramic stone roaster. No instructions were provided. How would I use to create your results?
Hi, I don’t know how to cook sweet potatoes with ceramic stone roaster. Sorry I couldn’t help.
Beautiful recipe. The result is nothing short of amazing, I’ve tried this method with just local honey sweet potato and they turned out awesome – sugar syrup was dripping from the potato, a thin layer of chewy sweet potato next to the skin followed by very soft flesh in the middle.
Hi, I’m glad to hear that this method was able to apply to cook the local sweet potatoes. Thank you for trying the recipe!
I got sweet Japanese potatoes. I tried your method but it came out totally dry From skin to inside. I was using convection oven, 190deg for 90mnts, then leave it there for 60mnts. What could be the issue? Thank you! I d give it another try.
Hi, Fenny. I’m sorry to hear about your result. I guess that might have caused your oven is stronger than mine, or the sweet potatoes are thinner or drier than usual. If the size of your sweet potatoes is less than 4-5 cm in diameter, I recommend to reduce the baking time to 1 hour or less. And, You’d better check if the potatoes are cooked through after the baking time. Or maybe you might as well reduce the baking temperature to 160 degrees. I hope it will help!
Thanks for the great recipe. For what its worth, a large amount of Murasaki potatoes (they look exactly like your picture) are grown right here in Eastern North Carolina. We get ours from Farm Pak farms (farmpak.com). Not sure if they ship, but we go to the office and get a 40 lb box for $25. You might contact them to see about shipping, or what stores carry their potatoes.
Wow! I just tried making this for the first time and followed your recipe exactly. It came out perfectly! I’ll never buy yaki oimo again now that I can make it so easily. Thank you!
I’m so glad to hear that you said the yaki imo is like a store bought! Thank you😊
Do you turn on the oven fan or just the heat?
My oven is automatically run fan. So I think you should turn on the fan!
This was perfect! I could never figure out how to get the potatoes like they do at our favorite Japanese grocery store and this was it–it is literally dripping in sugar. Doomo Arigatou!
I’m very happy to hear you enjoyed this recipe! Thank you for your kind words!
Can I remove the skin when bake, and I wan to add in Cheese and Bacon. What do you advise. Thank you.
I adjusted the baking time of this recipe to bring out the sweetness of sweet potatoes and eat as a dessert. If you remove the skin, sweet potatoes may be dried up. Also, I think this baking time is too long to cook cheese and bacon. So you might want to use other recipe. But thank you for stopping by my site!
Hi. You said preheating isn’t necessary. In that case when does the timer start? At the moment we put in the japanese sweet potatoes inside the oven or when the oven reaches 374F
Hi! The time starts at the time you put the sweet potatoes in the oven!
Can I cook the potatoes the night before, and leave them in the oven overnight? Then just re-heat a little before enjoying them for breakfast?
I haven’t done it before. But I think it’s no problem!
Hi! I bought 2kg of quality sweet potatoes, and wanted to do them justice! The first 2 wasn’t so great, I wrapped in foil at 210degrees Celsius for 1hr, they turned out steamed like. Then I chanced across ur blog recipe, voila, I enjoyed Super sweet caramelised sweet potatoes for lunch today! Thank you so much! Your recipe rocks!
Sending u ❤️❤️❤️ from Singapore! xx
Thank you so much for your kind words! I’m really happy that you enjoyed Japanese sweet potatoes in Singapore!😊❤
I followed your recipe exactly and my Japanese Sweet Potatoes turned out the best I have ever made! Thank you! These are a game changer and so delicious!!
I’m glad you like it! Thank you for trying the recipe!
Tried your recipe today and one of the sweet potatoes exploded after around 50 min of baking 🤣. I switched off the heat and left the sweet potatoes in there for another 30min. The skin wasn’t crispy but the insides were v soft. Temperature was too high you reckon? Thanks for sharing your recipe!
Thank you for trying the recipe! About the explosion of sweet potatoes, I looked it up online and according the site that I saw, It sometimes happens if a sweet potato contains a lot of moisture on the inside. It says that you can prevent the explosion by piercing sweet potatoes with a fork before baking. Because it provides an escape way for the hot steam come out from the inside. I’ve never had a potato explode on me. But I’ll add a step to poke holes in the sweet potatoes in my recipe for the safety. Thank you for your feedback. I really appreciate it!
Maybe because the sweet potatoes were not the freshest. They were air flown from Japan and were prob a week old by the time I got them from the supermarket.
Umm… Sorry, I’m not sure. But you may be right. I hope Japanese sweet potatoes will be sold in other countries!
Thanks so much for sharing I’m so excited to try this treat at home! Just confirming, you didn’t poke holes in the potatoes before popping them in the oven?
Thank you for stopping by my site! I don’t poke holes in the potatoes. I hope you will love the sweet potatoes!
When I responded to your comment asking “whether I poke holes in the potatoes”, I answered that I don’t do that. But I have got feedback that a sweet potato was exploded in the oven. So I recently added a step of poking holes in the potatoes after I heard that. I will tell you this, just in case.
Hi. I didn’t see in the instructions about preheating the oven. Does it mean preheating isn’t necessary?
Yes, it means preheating isn’t necessary!
Hi! momen, I’m glad i came to your blog, I was in search for this recipe. Caramelized on the outside and moist and creamy on the inside. I can’t wait to try it. I don’t know the difference between branded and unbranded sweet potato, since I’m currently living in Okinawa, do you have any recommendation where to get a good variety and what store? i tried buying at regular store and it seems the taste is different. Thank you
Sorry, I don’t know about stores you can get good quality of sweet potato in Okinawa. In Tokyo, I always buy them at a regular store. But lately, I can’t see a good variety in such stores. Because sweet potato season is almost over. It’s not what you are asking, though internet shop would be the best way to buy them at this time. My most recommended sweet potato can be bought from here. https://goodroots.official.ec
You can also order directly by phone / mail in their profile page of instagram. https://instagram.com/furusho.kanshoten?utm_source=ig_profile_share&igshid=3tre2ac2i374
They said still have some left. (They normally sell sweet potato from November to April.) I hope this will help.
Thank you momen, I’ll definitely try the stores you recommended. I bought good quality raw sweet potato from the truck that sells the roasted sweet potato that I always liked, I tried to pursuey him where he bought his sweet potatos, he said “puro no ichiba” which was translated to “professional market”. Anyway, I tried your method and it works! caramelized on the outside and creamy on the inside! Thank you so much!
I’m so glad to hear that! Asking to a seller of the truck is a nice idea to reach a good quality sweet potato, which I couldn’t come up with. Thank you for your comments and have a good time in Okinawa!