Glazed Japanese Sweet Potatoes (大学芋 - Daigaku Imo)
Daigaku Imo is a popular snack food in Japan that's often found in street stalls and festivals around Japan, alongside other traditional snacks like Taiyaki and Mitarashi Dango. Traditionally, it's made by double frying Japanese sweet potatoes before glazing them in a sticky syrup.
In my Japanese sweet potato recipe I like to use a three-step process of steaming, frying, and glazing the sweet potatoes. This cooking method creates a lasting crisp exterior while the interior remains tender and moist. It may take a little more prep time, but the results are definitely worth it!
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Why This Recipe Works
- Steaming the Japanese sweet potatoes first gives them a soft and creamy texture.
- Deep frying the steamed sweet potatoes gives them a uniform golden-brown crust, which keeps them from falling apart when you glaze them.
- Glazing the outside of the sweet potatoes with a crisp candy coating instead of double frying them keeps them from getting dry and mealy and results in ideal textures on the inside and outside.
Ingredients for Glazed Japanese Sweet Potato
- Japanese Sweet Potatoes - Japanese sweet potatoes have red skin and yellow flesh, with less moisture and more starch than their North American relatives. This makes them well suited for frying.
- Rice Syrup - rice syrup is made by saccharifying the starch in rice, which converts it into sugars (primarily maltose). At room temperature, it is very thick (like cold honey) and has a slick surface that gives the Daigaku Imo a beautiful, shiny, lacquer-like coating that adheres well to the crispy fried flesh and smooth skin.
- Sugar - Maltose tastes half as sweet as regular sugar, so I like to add a bit of evaporated cane sugar (sucrose) to my Japanese sweet potato recipe to give it a slightly sweeter taste. If you can't find evaporated cane sugar, white sugar can be substituted. If you want yours to taste less sweet, you can just use the rice syrup. A light sprinkling of salt can help balance out the candy-like sweetness.
- Black Sesame Seeds - The black sesame seeds add some visual contrast and contribute to the crisp texture of the candy coating while imbuing a wonderfully nutty flavor to the mix.
How to Make Daigaku Imo
The first thing you need to do is prepare the Japanese sweet potatoes. I start by giving them a good wash, being careful not to scrub the skin off. Then I trim both ends off of each one and cut them up using rangiri.
To do this, cut off a chunk of sweet potato at a 45-degree angle and then turn it 90 degrees before cutting off another chunk at the same angle. This should allow you to cut the tapered tuber into pieces that are roughly the same size and thickness. As you cut the sweet potato, put the pieces into a medium bowl of cold water to keep them from oxidizing.
Fill a heavy-bottomed pot with 2 inches of vegetable oil and preheat it to 340 degrees F (180 C).
Rinse any excess starch off the cut sweet potatoes, drain them, and then place them in a frying pan with ¼ cup of water. Cover the pan with a lid, and then bring the water to a boil over medium-high heat. Steam them for another 5-6 minutes, or the time it takes for most of the water to evaporate.
Remove the lid and allow any remaining water to evaporate. Once the sweet potatoes are no longer wet, add them to the preheated oil and deep fry them for about five minutes or until they're golden brown. Be sure to turn them over regularly so they brown evenly.
About 2 minutes before the sweet potatoes are done, add the rice syrup and sugar to the frying pan you used for steaming and heat the mixture until the sugar is melted. Use tongs to drain and transfer the fried sweet potatoes directly into the syrup, and then toss everything together to coat the Daigaku Imo evenly.
The mixture should be very sticky to ensure the sugar forms a crisp shell, but if it becomes impossible to mix or it seems like it's starting to burn, add a spoonful of water to loosen things up. Finish the Daigaku Imo by tossing in the black sesame seeds. To balance the sweetness, you can also sprinkle in a pinch of flaky salt.
FAQ
Daigaku Imo literally means "university potato" in Japanese, and it's a sweet snack food made by frying and glazing Japanese sweet potatoes in thick sugar syrup.
Despite having a relatively short history, it's unclear exactly who created this treat. The consensus is that it was created near one of Tokyo's major universities in the late 1920s or early 1930s. It quickly became a popular snack food amongst hungry college students, most likely where it got its name.
Daigaku has three syllables, and Imo has two syllables. They're pronounced as follows:
dai like die
ga like gone
ku like cool
i like even
mo like motor
All sweet potatoes were first cultivated in Central and South America, but they were brought to Japan by the Portuguese in the 1600s. Known as satsumaimo (サツマイモ) in Japan, they quickly became a staple crop due to their ability to make up for any shortfalls in the rice harvest. Through selective breeding, Japanese sweet potatoes have become a unique set of cultivars characterized by red skin and pale yellow flesh that becomes vibrant yellow as they're cooked. They tend to be sweeter than Western orange varieties and have a lower moisture content, which can make them dry if they're not prepared properly.
Most Japanese grocery stores will carry them, as well as other Asian grocery stores. Some larger grocery chains in the US have started selling them, like Trader Joe's, Sprouts, and Whole Foods. Look for signs and labels that identify them as Japanese varieties.
Japanese sweet potato varieties are excellent for baking, steaming, stir-frying, or mashing. Their chestnut-like flavor even makes them a popular ingredient for sweet recipes.
Baking is the most popular way to serve them in Japan, and yaki imo vans can be found roaming the streets of most Japanese towns in Autumn. There are even chains of high-end stalls in major cities serving perfectly baked potatoes using traditional cooking methods such as in clay urns.
The red or purple skins of Japanese sweet potatoes are loaded with vitamins, fiber, and texture and provide a great color contrast to the interior. That said, if you're not into eating the sweet potato skins, you can peel them off. They will be slightly more prone to crumbling, so you'll need to handle them gently.
This Japanese sweet potato recipe should work with other kinds of sweet potatoes as long as the variety you are using is relatively low in moisture. Higher moisture varieties, such as the orange-fleshed sweet potatoes often found in North America, will likely cause the candy coating to dissolve.
This recipe is entirely plant-based as long as you use vegan sugar. Some versions use honey or are fried in lard, though, so if you are ordering it at a restaurant, be sure to ask.
After steaming them, you can coat them in a generous amount of oil and then bake them in a single layer on a parchment-lined baking sheet in the oven. They will not brown quite as evenly as frying them and won't be as moist on the inside. It's important to use high heat and stir them often. They're going to absorb a similar amount of oil as deep-frying, and this oven method takes longer and yields inferior results, so I don't recommend it.
You can pan fry them after steaming them; however, the browning will be uneven. They also tend to fall apart as you glaze them because they don't get a uniform crust.
Other Japanese Snack Recipes
- Crispy Ramen Snack
- Butter Mochi
- Ohagi
- Sata Andagi (Okinawan Donuts)
📖 Recipe
Units
Ingredients
- 450 grams Japanese sweet potatoes (satsuma imo)
- Vegetable oil (for deep-frying)
- ¼ cup water
- ¼ cup brown rice syrup (80 grams)
- 20 grams evaporated cane sugar (about 2 tablespoons)
- 2 teaspoons black sesame seeds
Instructions
- Trim the ends off the 450 grams Japanese sweet potatoes and cut them rangiri by cutting off a chunk at a 45-degree angle from one end and then turning it 90 degrees and cutting another at a 45-degree angle. Repeat until you've cut all of the tubers into pieces that are roughly the same size and thickness.
- Soak the cut pieces in cold water to keep them from oxidizing.
- Preheat a pot with 2 inches of Vegetable oil to 340 degrees F or 180 C.
- Rinse and drain the sweet potato pieces and then put them in a frying pan along with the ¼ cup water. Cover with a lid and steam over medium-high heat until almost no boiling water remains.
- Open the lid, let any remaining water boil off, and then transfer the sweet potatoes into the hot oil.
- Fry these until they're golden brown (about 5 minutes), turning them over regularly to ensure they brown evenly.
- When the sweet potatoes are almost done frying, add the ¼ cup brown rice syrup and 20 grams evaporated cane sugar to the pan you used for steaming and start heating the mixture to dissolve the sugar.
- Transfer the fried pieces directly from the oil into the glaze and toss them around in the syrup to coat them evenly. If the mixture has gotten too sticky to glaze, you can add a spoonful of water to loosen it up. Add the 2 teaspoons black sesame seeds and toss to distribute evenly.
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