Onsen Tamago (Hot Spring Eggs)

Onsen Tamago is a type of boiled egg that is prepared using an interesting Japanese cooking method. You can enjoy the delicate, custard-like whites and the rich, creamy yolks.

Jump to:

• What is Onsen Tamago?
• Unique solidification process
• Temperature control methods
• Important precaution
• Condiment options
• Notes bofore cooking
• 📋Step-by-step recipe
• Tips on how to make
• Recipe card

What is Onsen Tamago?

Onsen Tamago is a boiled egg dish that is cooked by being immersed in hot water for a certain period of time, resulting in a semi-cooked, creamy yolk and a partially set white. "Onsen" means hot springs, and "Tamago" refers to eggs. It earned its name because this dish was traditionally cooked in hot springs. Sometimes called 'Ontama' for short.

This dish, created solely from eggs, has a unique texture distinct from that of both soft-boiled eggs and poached eggs. It is delicious on its own and is a familiar topping in salads, rice bowls, udon, and curry in Japan. The taste of eggs directly affects the flavor of the dish, so it is advisable to use fresh, high-quality eggs if possible.

Unique solidification process

The distinctive feature of this dish lies in the unique state of the eggs.

While a typical boiled egg solidifies from the egg white first, onsen tamago solidifies from the yolk first. The reason is that this dish is made by immersing the eggs in water at a temperature of around 167℉ (75℃).

Proteins in the egg whites and yolks solidify at different temperature ranges. The yolk begins to solidify at 149℉ (65℃) and reaches full solidity at 158℉ (70℃), while the white starts to solidify at 136℉ (58℃) but will not completely solidify until it reaches 176℉ (80℃).

In other words, onsen tamago is created by utilizing the difference in the temperature ranges at which the proteins in the yolk and white coagulate. The yolk is heated to a rare, semi-cooked state, while the white remains custard-like, partially set, resulting in a texture similar to a midpoint between raw eggs and boiled eggs.

Temperature control methods

Proper temperature control is crucial for making onsen tamago.

If you have a food thermometer, heat water in a pot and measure its temperature. Considering that the water temperature will decrease over time, adding the eggs when it reaches 167-176℉ (75-80℃) will yield optimal results.

However, this method is not commonly used in Japan. Instead, one of the following methods, which do not require a thermometer, is often employed:

• Place an egg in a heatproof container and pour boiled water into it.
• Pour tap water (room temperature water) into the pot of boiled water before adding eggs.

The first method works well when cooking a single egg, while the second method is suitable for cooking multiple eggs.

With the method of pouring boiled water, both the container and egg absorb the heat, resulting in a water temperature of around 167℉ (75℃). On the other hand, in the method of adding tap water, the optimal temperature is reached by mixing boiled water with tap water.

While both methods are included in this recipe, depending on factors such as your elevation, or whether you live in a cold or warm region, the boiling point of water or the temperature of tap water may differ, causing the recipe not to work as expected. In such cases, adjust the amounts of boiled water or tap water to achieve a temperature of around 167℉ (75℃) according to your local conditions.

Important precaution

Before preparing this dish, it is important to note that it carries a slight risk of food poisoning.

Typically, Salmonella bacteria, the main cause of food poisoning from eggs, can be killed by heating at 167℉ (75℃) for at least 1 minute or 149℉ (65℃) for at least 5 minutes. Onsen tamago is made by immersing eggs in hot water at around 167℉ (75℃) for about 15 minutes, but as the water temperature decreases over time, there is a possibility that Salmonella bacteria may not be completely killed.

While eggs distributed in developed countries are likely safe, if there are hygiene concerns regarding eggs in your area, it is recommended to use pasteurized eggs. Additionally, it is advisable for individuals with weakened immune systems, such as pregnant women, the elderly, and infants under 2 years old, to refrain from consuming this dish.

Condiment options

Onsen tamago doesn't require seasoning when used as a topping for salads, rice bowls, udon, and curry. However, when enjoyed on its own, it is common to drizzle it with dashi soy sauce, mentsuyu (Japanese noodle soup base), or shiro dashi (light-colored soup base). My personal recommendation is definitely dashi soy sauce.

This recipe includes a simple way to make dashi soy sauce, but if you are interested in experiencing a more authentic dashi soy sauce, please refer to the recipe on the linked page. You can use it in various other Japanese dishes as well.

Notes bofore cooking

This recipe shares two methods for making onsen tamago.

The first method, which involves pouring boiled water into a container, is very easy to make, but it is not recommended when cooking multiple eggs, as it can be easily influenced by factors such as egg temperature, container material, and ambient temperature. It is suitable for making just one.

When you want to make multiple eggs at once, the second method that uses a pot is a better choice.

📋Step-by-step recipe

Ingredients

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Instructions

🕒 Total 16-20 mins

The easiest method using boiled water (suitable for a single serving only)

Step 1
Place the egg in a heatproof container* and pour freshly boiled water into the container, avoiding direct contact with the egg as much as possible. Cover the container with a lid or plastic wrap and let the egg sit for 15 minutes.

* Make sure to use a container that is large enough for the egg to be completely submerged when the specified amount of water is added.

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Step 2
Remove the egg from the container and cool it under running water or in ice water.

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The method using a pot (suitable for multiple servings)

Step 1
Fill a pot with water and bring it to a boil. Once boiling, turn off the heat and add tap water to lower the temperature of the water in the pot. Remove the pot from the stove.

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Step 2
Carefully add eggs to the pot one by one using a ladle to prevent them from cracking, then cover with a lid. Let them sit for 15 minutes.

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Step 3
Remove the eggs from the pot and cool them under running water or in ice water.

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Steps to make simple dashi soy sauce (If you already have dashi soy sauce, mentsuyu, or shiro dashi on hand, skip this section.)

Step 1
Put sake and mirin in a pot and simmer over low heat for 1-2 minutes until the alcohol content evaporates (until the distinct aroma dissipates).

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Step 2
Pour soy sauce into the pot and heat it until it begins to boil. Once boiling, turn off the heat, add bonito flakes, and let them steep for 2 minutes. Strain the mixture through a fine mesh sieve into a container. Simple dashi soy sauce is ready.

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For serving

Step 1
Crack the onsen tamago into bowls, drizzle with dashi soy sauce, and top with green onions to taste.

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To Store

You can store it in the refrigerator for up to 3 days with the shell still on.

Tips on how to make

• After soaking the eggs in hot water, cool them under running water or in ice water. This helps prevent the eggs from continuing to cook due to residual heat and makes it easier for the egg whites to separate from the shell when cracked.
• If you reside in a high-altitude, cold, or hot region, the boiling point of water or the temperature of tap water may differ, causing the recipe not to work as expected. In such cases, adjust the amounts of boiled water or tap water to achieve a temperature of around 167℉ (75℃) according to your local conditions.

Recipe card