How to Make Supermarket Unagi Taste Restaurant-Level

Hi, everyone! It’s Japan’s eel-eating day!

The correct name is Doyō no Ushi no Hi. It refers to a Day of the Ox in the traditional Japanese calendar that falls during the seasonal period before autumn.

In Japan, it is customary to eat unagi, or freshwater eel, during the hottest part of summer. Unagi is considered a special and nourishing meal, so Doyō no Ushi no Hi gives us the perfect excuse to enjoy this rather expensive treat, recharge our bodies, and survive the summer heat!

Because unagi can be costly, we want to make the most of it. (¥1,980/ $12)

Today, I am sharing a simple way to make supermarket unagi soft, fluffy, smoky, and restaurant-level.

Supermarket unagi is convenient and delicious, but after being cooked, packaged, and chilled, its texture can become a little firm. The sauce may also be thick and overly sweet, and it can burn before the eel is properly heated.

But don’t worry. It is surprisingly easy to improve.

What Is Supermarket Unagi?

In Japan, supermarket eel is almost always sold already cooked and coated in a sweet soy-based sauce. This cooking style is called kabayaki.

Kabayaki unagi is usually butterflied, grilled, and glazed with a sauce made from soy sauce, mirin, and sugar. It is convenient because the eel is already fully cooked, but reheating it directly in the microwave can sometimes make it dry or rubbery.

The best way to reheat supermarket unagi is to first restore its moisture, then grill it briefly to recreate a smoky, caramelized surface.

Why Rinse the Sauce Off Supermarket Unagi?

It may sound strange, but the first step is to gently rinse off the sauce already coating the eel.

The original sauce can be quite thick, and because it contains sugar, it burns very easily under a grill. Washing it off allows the unagi to heat evenly without scorching.

Do not worry about losing flavor. We will add fresh homemade unagi sauce later.

Rinse the eel gently under water until the surface is no longer slippery. Then pat it dry carefully with paper towels.

Unagi is delicate, so handle it gently to prevent it from breaking apart.

Homemade Unagi Sauce

A fresh homemade sauce gives the eel a glossy finish and a richer, cleaner flavor.

Ingredients

• ½ cup mirin
• 3 tablespoons granulated sugar
• ½ cup soy sauce

You can add a little more sugar if you prefer a sweeter sauce.

I like granulated sugar because it gives the sauce a clean sweetness, but you can use your favorite type of sugar.

Method

Pour the mirin into a small saucepan and bring it to a boil.

Let it boil briefly to cook off some of the alcohol.

Add the sugar and stir until completely dissolved.

Pour in the soy sauce, reduce the heat to low, and simmer for a few minutes until the sauce has reduced slightly.

Do not reduce it too much. The sauce will continue to thicken as it cools.

How to Reheat Supermarket Unagi So It Becomes Soft and Fluffy

Cut the unagi into pieces that will fit comfortably inside your frying pan.

Place the pieces in the pan and drizzle over about 1 tablespoon of sake.

Cover the pan with a lid and cook gently over medium-low heat.

The sake creates steam inside the pan, restoring moisture to the eel and helping the flesh become soft, light, and fluffy.

Continue steaming until the unagi is heated through and begins to puff up slightly.

Grill the Unagi for a Smoky Restaurant-Style Finish

Carefully transfer the steamed unagi to a grill, broiler, or toaster oven.

Grill it until the surface begins to bubble.

Turn the eel over gently and grill the other side.

Traditional unagi restaurants often cook eel over charcoal, which gives it a wonderful smoky and toasted aroma. A home grill cannot completely recreate charcoal cooking, but this step gives the supermarket eel a much deeper, more restaurant-like flavor.

Turn the unagi back over and brush it generously with the homemade sauce.

Grill it again briefly until the sauce becomes glossy, caramelized, and slightly bubbling.

Watch it carefully. The sugar in the sauce can burn quickly.

How to Serve Unagi Don

Fill a bowl with freshly cooked, steaming-hot Japanese rice.

Drizzle over as much homemade unagi sauce as you like.

Place the grilled unagi on top. You can cut it into smaller portions to make it easier to eat.

Finish with a little sanshō pepper.

Sanshō is optional, but its citrusy aroma and gentle numbing heat balance the richness of the eel beautifully.

Serve your unagi don with Japanese pickles or a light soup.

I served mine in a beautiful red lacquerware bowl from Nakagawa Masashichi Shoten. Beautiful tableware can make an everyday meal feel even more special.

The Result

The inside of the unagi is soft, fluffy, and almost melt-in-your-mouth.

The outside is glossy, smoky, lightly caramelized, and beautifully grilled.

It is rich, comforting, and full of flavor—the perfect meal to recharge your body and survive the summer heat.

With only a few extra steps, supermarket unagi can taste remarkably close to the eel served at a special unagi restaurant.

Happy Doyō no Ushi no Hi!

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Frequently Asked Questions

Is supermarket unagi already cooked?

Yes. Supermarket unagi in Japan is generally sold fully cooked, usually in the kabayaki style with a sweet soy-based glaze.

Should I wash the sauce off supermarket unagi?

Rinsing off the original sauce can help prevent burning when you grill the eel. You can then replace it with fresh homemade sauce.

What is the best way to reheat unagi?

Steam it gently with a small amount of sake to restore moisture, then finish it under a grill or broiler for a smoky, caramelized surface.

Can I use a toaster oven?

Yes. A toaster oven works very well for reheating and lightly grilling supermarket unagi. Watch it closely because the sauce can burn quickly.

What is Doyō no Ushi no Hi?

Doyō no Ushi no Hi is a traditional Day of the Ox that occurs during the seasonal period before autumn. In Japan, people commonly eat unagi on this day to restore energy during the summer heat.

What is kabayaki?

Kabayaki is a Japanese cooking method in which eel is butterflied, grilled, and repeatedly brushed with a sweet soy-based sauce.