Slowly roasted sweet potato at low temperature is the most delicious and healthy snack that Japan offers. The subtle burnt sweet aroma coming from a street food truck in Japan is just irresistible. And the good news is that we can achieve this at home.
What is Yaki Imo?
Those baked or roasted Japanese sweet potatoes are called “Yaki Imo” or “Ishi Yaki Imo”. Ishi yaki imo is sweet potato baked in hot stones or pebbles. Surprisingly roasted sweet potato is consumed as a snack rather than a side dish in Japan. There are many yakiimo street venders in Japan selling delicious freshly baked sweet potato by its weight.
Especially in winter, you will see the Yaki Imo or Ishi Yaki Imo sold everywhere in Japan. Hearing a Yaki imo food truck coming around (because they call out with speaker) is a typical Japanese winter scene. Why is sweet potato sold more in winter? Because sweet potatoes are harvested in autumn.
Types of Sweet potato
Sweet potato is called “Satsuma Imo”. It is named after Satsuma Region in Kyushu island where the sweet potato was first introduced to Japan. When the Japanese refer to sweet potato, they are the purple sweet potatoes with white flesh. The white flesh turns a beautiful golden yellow colour when it is cooked.
A well-known sweet potato for roasting is “Naruto-Kintoki” and “Annou-imo”. Even though we can get purple sweet potatoes outside of Japan, those particular types are not readily available.
But don’t despair. There are ways to cook sweet potatoes just like the stone-baked roasted potatoes you can buy from the street food truck in Japan. And it is just so simple! NO matter what equipment you use. Baking sweet potatoes slowly at low temperature is the key for deliciously sweet baked sweet potatoes.
Sweet potatoes contain a lot of enzymes called amylase. This amylase breaks down the starch into sugar at temperatures up to 65°C (150°F). Thoroughly baking at low temperature increases the enzymatic action and breaks down many starches into sugar thus increasing the sweetness.
1. Choosing good sweet potato
How to pick a good sweet potato suitable for roasting at home? Choose ones that are plumply round 6-8 cm (2.5-3 inch) in diameter and both ends are not shrivelled. The skin is smooth and vivid and uniform in colour. Furthermore, sweet potatoes with fewer hair roots will have smooth texture.
2. Oven roast
Wash sweet potatoes and wrap them tightly with aluminium foil. Place them in an oven. You don’t need to preheat the oven. Set the temperature at 160°C (320°F) and bake them carefully for about 90min. Test by inserting a skewer, if it is soft turn the oven off and leave them in the oven for another 10 minutes.
3. Frying pan roast
This is the method I used. Wash the sweet potatoes and wrap with alfoil tightly. Arrange them on a frying pan or a skillet. Place a lid over and roast for about 50 to 60 minutes. Turning the sweet potatoes every 15 minutes. Turn the heat off when the softness is checked with a skewer. Leave the sweet potatoes to rest.
Handy glove “Gunte”
Those cotton gloves are called “gunte” (pronounced like goo-n-tay) and are a working glove. They become very handy when you need to handle hot food. I often use these working gloves in my cooking. You see this in making the extra thick and fluffy Japanese pancakes too.
Other sweet potato recipes to check
- Japanese candied sweet potato “Daigaku Imo”
- Japanese rice porridge with sweet potato
- Pureed Sweet potato and chestnuts “Kuri Kinton”
- Christmas Sweets : Edible Pine cones
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Roasted Sweet Potato
- a frying pan/a skillet
- aluminum foil
- 3 purple sweet potatoes *1
- Wash the sweet potatoes
- Wrap the sweet potatoes with aluminium foil tightly.
- Arrange the aluminium foil wrapped sweet potatoes on a frying pan or a skillet over low heat.
- Place a lid over the frying pan or the skillet and roast the sweet potato slowly for about 1 hour. *2
- Turning the sweet potatoes about 90 degrees every 15 minutes.
- Insert a skewer, if the sweet potatoes are soft, turn the heat off and serve.