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, along with other traditional snacks like Taiyaki and Mitarashi Dango. It's traditionally made by double frying Japanese sweet potatoes before glazing them in a sticky syrup.
In my version, I like to use a three-step process of steaming, frying, and glazing the sweet potatoes, which creates a crisp lasting exterior while the interior remains tender and moist.
Why This Recipe Works?
- Steaming the Japanese sweet potatoes first makes them soft and creamy.
- 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.
Ingredients for Glazed Japanese Sweet Potato
- Japanese Sweet Potatoes - Japanese sweet potatoes have red skin and yellow flesh, and they tend to be starchier than their Western relatives. This makes them well suited for frying.
- Rice Syrup - rice syrup is made by saccharifying the starch in rice, which converts them 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 lacquer-like sheen.
- Sugar - Maltose tastes half as sweet as regular sugar, so I like to add a bit of sucrose to the mix to give it a slightly sweeter taste. If you want yours to taste less sweet, you can just use the rice syrup.
- 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 potato and cut them up using rangiri.
To do this, cut off a chunk of sweet potato at a 45-degree angle, and then turn the potato 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, be sure to put the pieces into a 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).
Wash any excess starch off the 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 the potatoes for another 5-6 minutes or until most of the water has evaporated.
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 the potatoes 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.
Other Japanese Snack Recipes
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 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 varieties, but they also have a lower moisture content, making them dry if they're not prepared properly.
As long as the sweet potato you are using is relatively low in moisture, this should work. Higher moisture varieties such as the orange-fleshed variety often found in the US 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 on a parchment-lined sheet pan in the oven. They will not brown quite as evenly as frying them, and they won't be quite as moist on the inside. They're going to absorb a similar amount of oil as deep-frying, and this 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.
- 450 grams Japanese sweet potato (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
- Trim the ends off of the sweet potato and cut it rangiri by cutting off a chunk of potato at a 45-degree angle from one end and then turning the potato 90 degrees and cutting another chunk off at a 45-degree angle. Repeat until you've cut all of the potatoes into pieces that are roughly the same size and thickness.
- Soak the cut potatoes 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 potatoes and then put them in a frying pan along with the ¼ cup of water. Cover with a lid and steam over medium-high heat until there is almost no water remaining.
- Open the lid, let any remaining water burn 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 rice syrup and sugar to the pan you steamed the potatoes in and start heating the mixture to dissolve the sugar.
- Transfer the sweet potatoes 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 sesame seeds and toss to distribute evenly.
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