Candied Sweet Potato (Daigaku Imo) | Sudachi Recipes (2024)

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What is Daigaku Imo?

Daigaku Imo (大学芋) is a classic Japanese sweet snack made from purple Japanese sweet potatoes. They are usually cut into pieces, deep fried, coated in a sweet crunchy candy glaze and then sprinkled with black sesame seeds.

This snack is typically eaten in Autumn, a time when desserts made with seasonal produce such as Japanese squash (kabocha), chestnuts (kuri) and sweet potatoes (satsumaimo) line the shelves of supermarkets, convenience stores and bakeries across Japan. Daigaku Imo is one of my favourite snacks to enjoy as temperature drops and the days get shorter!

A Brief History of Daigaku Imo

It is believed that Daigaku Imo appeared in a sweet shop near Tokyo university around the beginning of the Showa period (1926-1989). The dish was supposedly inspired by the Chinese method “ba si” where ingredients such as apples, sweet potato and taro are fried and coated in a simple candy made with sugar and water. “Basi Digua” (拔丝地瓜) is the Chinese version of candied sweet potato and is known as “Chuuka Poteto” (中華ポテト) or “Chinese Potato” in Japanese.

You might wonder if there’s any difference between the Chinese and Japanese versions of this dish. After all, it’s just a candied sweet potato right? Well actually, there are a few characteristics that set daigaku imo apart from the original Chinese version.

Firstly, daigaku imo is always sprinkled with black sesame seeds, this is iconic for this dish and never left out. Secondly, the candy coating in the Japanese version is often flavoured with a hint of soy sauce for added depth and color. A few other small differences include leaving the skin on (the Chinese version is usually completely peeled) and eating them warm/room temperature.

Why is it Called “Daigaku Imo”?

The name “Daigaku Imo” (大学芋) means “University Potato” in English and there are a few different theories about the unusual name and origins of this dish.

• Some say Daigaku Imo was sold in a sweet shop near Tokyo university and became a hit with the students in the area.
• Japanese sweet potatoes are cheap and filling, the perfect ingredient for students on a budget.
• It’s a potential money maker. Cheap to buy, easy to turn a profit – rumour has it that some students would make and sell candied sweet potatoes to help fund their college fees.
• They’re delicious – Daigaku Imo are simply loved by university students!

Whatever the origin, there’s no doubt that they’re a well loved sweet amongst all Japanese people, not only students!

How I Developed This Recipe

For me, the perfect Daigaku Imo needs to be fluffy in the middle and crispy on the outside. To achieve this, I needed to create a candy coating that wouldn’t compromise the crispy outside of the deep fried sweet potato.

After many attempts and experiments with different techniques, I found that the secrets lie in the way its cut, the frying method and the type of coating. I opted for a hard candy rather than a sauce or glaze.

I believe I’ve created a deliciously crispy Daigaku Imo similar to my favorite store-bought version. I hope you try my recipe and love it as much as I do!

Ingredients & Substitution Ideas

For this recipe, you will need the following ingredients:

• Japanese Sweet Potato: Specifically “sastumaimo”, also known as the “murasaki potato” in English (not to be confused with the Okinawan sweet potato that is purple inside). Satsumaimo is especially sweet and dry compared to other kinds of sweet potato, I don’t recommend using other varieties. You should be able to find Japanese sweet potato in Asian supermarkets.
• Water: To soak the sweet potato and remove excess starch
• Salt: Helps draw out the starch and flavor the sweet potato. Use regular sea salt for this.
• Oil: For deep frying. Choose an oil with a mild flavour and high smoke point such as vegetable oil or canola.
• White Caster or Granulated Sugar: Works best to make the crunchy caramel coating.
• Mirin: For added depth and sweetness.
• Water: To dissolve the sugar.
• Rice vinegar: A small amount helps prevent crystallization.
• Soy Sauce: Adds a hint of color and depth.
• Black sesame seeds: For added crunch and decoration.

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3 Ways to Cut Sweet Potato for Daigaku Imo

There are a number of different ways to cut sweet potato for Daigaku Imo, so here I will cover 3 different ways to cut and include the pro’s and con’s for each method.

Rangiri (diagonal bitesize chunks)

The most common way to cut sweet potato for daigaku imo is using a technique called “rangiri”(乱切り). This kind of cut is used for long, cylindrical vegetables like carrots or cucumbers.

To cut rangiri style, first cut off the ends and then make thick diagonal cuts, rotating the sweet potato one quarter between each cut. Depending on the size of the potato, the middle pieces could end up being considerably bigger, in this case you can cut them in half. Try and cut the pieces to a similar size so that they finish cooking at the same time.

Rangiri style looks rustic and stylish in a homely way, it also ensures each piece has a good amount of skin. Some cons to rangiri cuts are that sometimes it can be difficult to keep the size of the pieces consistent (depending on the shape of the potato) and I personally find them a bit stodgy compared to the other styles.

Sticks (used in my recipe)

The second most common is the stick type, cut to a similar size as thick cut fries. This type is my personal favourite, the size is the best for snacking and the potato to candy ratio is just perfect in my opinion!

For the optimum size, I recommend slicing the sweet potato diagonally about 1.5cm thick (approx 1/2 inch) and then cut each slice into 3 sticks.

Because the pieces are smaller, they take up less space in the pot and you can use less oil. Due to the shape, it is also easier to fully coat each one with the candy, however because of the size, it does take a little longer to coat them all individually.

Rounds (thick slices)

While not as stylish at the other two, simply cutting the sweet potato into 1.5cm thick slices is the best of both worlds! Thinner than rangiri means they cook a little faster in the middle and cutting them is simple and straightforward. They also have a good amount of skin on each piece.

It might be a little more difficult to evenly coat the outside edge with caramel, but in terms of taste, texture and simplicity, this one has it all!

Visual Walkthrough & Tips

Here are my step-by-step instructions for how to make Japanese Candied Sweet Potato at home. For ingredient quantities and simplified instructions, scroll down for the Printable Recipe Card below.

How to Fry Japanese Sweet Potato for Daigaku Imo

STEP

Wash the surface of the sweet potato

The skin of Japanese sweet potato is very thin, it also has a beautiful colour and these are the two reasons why we generally eat them with the skin on. Of course, this means it needs to be washed well. Since the skin is quite delicate, I recommend washing it gently with warm water and a clean sponge or cloth, no need to scrub!

STEP

Cut

In my recipe, I cut my sweet potato into sticks. Cut off the ends, slice into 1.5cm (½ inch) rounds and then cut each round into three sticks.

This is my personal favourite way to cut sweet potato for Daigaku Imo, but if you want to cut it a different way, see above for alternative ways to cut sweet potato.

STEP

Soak

After cutting the sweet potato, place it in a bowl of cold water with a pinch of salt and soak for 5 minutes. Not only does this help remove the excess starch, but it also prevents discoloration and protects the potato from absorbing too much oil when we fry it.

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STEP

Dry thoroughly

After soaking, discard the water and dry each piece thoroughly with kitchen paper.

I don’t recommend air drying because they can become oxidized and discolored.

STEP

Start with cold oil

Next, transfer the sweet potato to a pot and pour in cold oil until all of the potato sticks are submerged. I use vegetable or canola oil, but you can use your preferred oil with a mild flavor and high smoke point.

Place the pan on the stove and turn on the heat on medium. Slowly bring the oil up to about 160-170°C (320-340°F). It helps to have a cooking thermometer for accuracy.

STEP

Fry

Once the oil is hot and the sweet potato is bubbling away, just wait for them to turn golden. If you’re unsure whether they’re cooked through, take out the largest piece and pierce it with a skewer or fork to test it.

From beginning to end, this technique took 15 minutes. Rounds should take the same time, rangiri a minute or so longer.

STEP

Drain

Once golden, transfer to a wire rack to allow any excess oil to drain off.

While they’re draining, we can move on to making the candy coating.

Making & Applying the Candy Coating

STEP

Mix the candy ingredients in a pan

Add sugar, mirin and water and mix to a pan while still cold (see tips & tricks for best pans to use for making caramel). I also add a small amount of rice vinegar to help prevent crystallization.

STEP

Heat until golden

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Place the pan on the stove over a low heat and stir until it starts to bubble. Once bubbling, stop stirring and leave it to turn golden. If it colors unevenly, tilt or rotate the pan, do not stir.

Once golden, dip a chopstick into the caramel and submerge it into cold water, if it turns hard then the caramel is ready.

STEP

Coat the potato

Add soy sauce, black sesame seeds and mix before adding the fried sweet potato.

Turn off the heat and roll each piece around the pan to get an even coating of caramel. (If the caramel starts to harden before you’ve finished coating, turn the heat back on to the lowest setting and turn it off again once it becomes soft. You might have to do this a few times if you’re making a big batch.)

STEP

Transfer to a non-stick surface

Transfer each piece straight to a non-stick surface with plenty of space between.

A heat-proof silicone baking mat (affiliate link) is ideal, but if you don’t have one, you can line a tray with baking parchment. (Keep in mind that some low quality baking parchments might still stick to the caramel, you can spray them with a very thin layer of oil to prevent any sticking.)

Cool for 5-10 minutes and enjoy!

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How to Store

Daigaku imo is best eaten on the day it’s made, preferably as soon as possible. This is because the candy coat tends to melt/deteriorate after a few hours, especially in humid or warm conditions.

Keep them in an airtight container in a cool place (but not in the refrigerator) if you plan to eat them later in the day.

I hope you enjoy this Daigaku Imo recipe! If you try it out, I’d really appreciate it if you could spare a moment to let me know what you thought by giving a review and star rating in the comments below. It’s also helpful to share any adjustments you made to the recipe with our other readers.Thank you!