By Vida Gustafson
I’ve had such a lot of fun researching this popular Japanese street food. When I say popular, I do mean popular, with iterations from donuts to fry flavoring, and seemingly endless homemade versions. The snack is ubiquitous in Japanese culture. It’s a bite sized deep fried sweet potato, candied in a sugar glaze with a touch of soy and black sesame seeds. What you end up with is crunchy on the outside, fluffy on the inside tasting of sweet umami goodness and nutty, earthy sweet potato. Daigaku Imo is translated as ‘university potato,’ so called because of its association with university students at the turn of the last century.
Be sure to use a sweet potato, not orange yam. Japanese sweet potatoes are magenta or red on the outside and pale yellow or white on the inside. I’ve been able to find them at most grocery stores and farmers markets in our area, especially in wintertime.
- 2 lbs sweet potato (Murasaki, Kotobuki or Satsuma are some varieties)
- 1 tsp salt
- 2 tbsp water
- 7 tbsp sugar
- 1 tbsp mirin (or 1/2 extra tbsp of sugar)
- 1 tsp vinegar (rice vinegar is best)
- 1 tsp soy sauce
- 1 tsp black sesame seeds
- flaked salt, for sprinkling
- 2 cups vegetable oil, for frying
Chop the sweet potatoes into 1-inch pieces, approximately, halving lengthways first if the root is very wide. As you chop, turn the vegetable a quarter of a turn in between slices, making irregularly shaped but equally sized pieces. This technique is called Rangiri, it’s very helpful in the chopping of irregularly shaped vegetables and produces interesting shapes with lots of surface area for your candy coating to stick to.
Soak the sweet potato in water with the teaspoon of salt added for 15 minutes.
Heat 2 cups of peanut, sunflower or safflower oil in a heavy bottomed pot. A Dutch oven or cast iron pot will work very well. While your oil is heating, drain the sweet potatoes and pat them dry.
Bring the oil up to approximately 320°F, to test without a thermometer, dip the handle end of a wooden spoon in the oil and watch for tiny bubbles to form.
Fry the sweet potato, in batches being careful not to overcrowd the pan, until lightly browned. Insert a toothpick or skewer into one to see if the sweet potato is cooked before removing the whole batch.
One batch takes approximately 10 minutes at a medium heat. Once everything is fried, set aside and in a large skillet or Dutch oven, stir together the water, sugar, mirin and vinegar, without turning the heat on. Once mixed, set the heat to low/medium, add the vinegar and soy once it starts to bubble. When it starts to bubble, turn the heat down and allow to cook for 5 minutes.
Add all the sweet potatoes and stir to coat in the sugar. Sprinkle over the sesame seeds and remove from the heat. Finish with flaked sea salt to taste.