Onsen Tamago literally means “hot spring eggs“ in Japanese. It refers to eggs that are slowly cooked in hot spring water to create silky egg whites and custard-like yolk. Here’s how you can make this delicious egg recipe at home.
In the past, I’ve shared some popular Japanese egg recipes on Just One Cookbook such as Omurice, Tamagoyaki, and Ramen Egg (Ajitsuke Tamago). Today I’ll add another popular dish to the egg recipe collection, and it’s Onsen Tamago (温泉卵).
What’s Onsen Tamago?
Onsen means hot springs, and tamago means eggs in Japanese. Why is the name “hot springs eggs”? Originally, eggs prepared this way were slow-cooked in Japan’s warm hot springs water.
What’s so special about these eggs? These eggs are perfectly poached inside its shell. While the whites are soft and silky, the yolk comes out firm but retains the color and creamy texture of an uncooked yolk. It’s basically the complete opposite of soft-boiled eggs, which are firm whites and soft egg yolk.
The Chemistry Behind Onsen Tamago
We can achieve this special texture because egg yolk and egg white solidify at different temperatures. Egg yolks solidify at 158°F (70°C) and egg whites solidify at 176°F (80°C). Therefore, if we maintain the cooking water at 149-154°F (65-68°C) for 30 minutes, we’ll get a perfect spherical poached egg, creamy and silky on the outside and firm on the inside.
This Recipe Works for Everyone
There are many ways to make the perfect onsen tamago, but this technique does not require a microwave, a thermometer, or any special cooking gadget.
Here are the highlights of this technique:
- Requires just a stove and pot (which I hope everyone has in their kitchen).
- Does NOT require a thermometer.
- Use refrigerated eggs. Some recipes require eggs to be “room temperature”, but the “room” temperature could be different depending on where you live.
- Not required to soak eggs in iced water after cooking, in case you don’t have ice cubes handy.
If you follow my recipe precisely, you should be able to achieve perfect onsen tamago as the final result. The only requirement is to use 4 large eggs. If you use different size eggs or reduce/increase the number of eggs, it will not work as the water temperature will change.
How Do you Enjoy Onsen Tamago?
You can enjoy onsen tamago with a dashi-based soy sauce (だし醤油) which is usually served as a part of Japanese breakfast. Also, you can place it on top of the steamed rice, splash some soy sauce over, mix, and enjoy; serve with gyudon, curry rice, soba noodle soup, and cold udon; or even mix with carbonara (my favorite!).
Now let’s get started! The best part about this recipe is you do not need to visit hot springs in Japan to enjoy these special eggs. Make the perfect onsen tamago right at home!
Disclaimer: Many people in the world including the Japanese consume uncooked eggs in their cuisine. However, according to the FDA, eggs should be cooked to 165 degrees °F (74 °C) in order to be considered safe. The perfect temperature for cooking onsen tamago is 149-154 degrees °F (65-68 °C), which is below the guideline. There is a risk of salmonella by consuming undercooked eggs.
Onsen Tamago (Japanese Slow-Cooked Eggs)
- 4¼ cups water (measure 4¼ cups and remove 4 tsp, to be precise)
- 4 large eggs (50 g each w/o shell) (refrigerated)
- ¾ cup tap water (¾ cup + 4 tsp, to be precise; colder than room temperature)
For the Sauce
For the Garnish
- green onion/scallion
- Gather all the ingredients. You will need a small heavy-bottomed saucepan (I use 1.5 QT); you will need to cover the eggs completely with the water.
- To the saucepan, add 4¼ cups water (measure 4¼ cups and remove 4 tsp, to be precise). Cover with a tight-fitting lid and bring it to a boil.
- Once boiling, remove the pot from the heat. Remove 4 large eggs (50 g each w/o shell) from the refrigerator. To the pot of hot water, add ¾ cup tap water that‘s colder than room temperature (¾ cup + 4 tsp, to be precise). Gently submerge the cold eggs in the hot water. Immediately cover and set the timer for 17 minutes.
- Meanwhile, make the sauce. Combine ¼ cup dashi (Japanese soup stock), ½ Tbsp mirin, and 1½ Tbsp soy sauce in a small saucepan and bring it to a boil. Add ⅓ cup katsuobushi (dried bonito flakes), turn off the heat, and let the katsuobushi sink to the bottom of the pan. After 30 seconds or so, strain through a sieve and set the sauce aside.
- Cut the green onion/scallion into thin slices and set aside.
- Once 17 minutes have passed, gently take the eggs out of the water and set them aside for 5 minutes.
- Enjoy the Onsen Tamago either warm or at room temperature. Crack the egg into a small bowl, pour the dashi-based sauce into the bowl, and garnish with the sliced scallion as a part of a Japanese breakfast. Try the egg on top of steamed rice with a splash of soy sauce. It‘s also delicious over Gyudon, Chicken Curry Rice, Soba Noodle Soup, and Cold Tanuki Udon.
- You can keep the uncracked Onsen Tamago for 1–2 days in the refrigerator. To reheat, remove it from the refrigerator and bring it to room temperature. To warm it up further, place it in a bowl of 160ºF (70ºC) water for 10 minutes. Do not reheat higher than that; otherwise, the heat will cook the egg. Keep any leftover sauce in the refrigerator for 4–5 days.