Onsen Tamago (温泉卵 - Hot Spring Egg)
With an ethereal texture like silky smooth custard, Onsen Tamago or hot spring eggs is a Japanese egg dish that's named after how it was traditionally cooked. Since not all of us have hot springs in our backyards, I'm sharing three different methods you can use to make these Japanese breakfast treats at home.
Table of contents
Why This Recipe Works?
- Making onsen tamago involves cooking the egg to a very specific temperature (145° F or 63° C). I've detailed 3 methods you can use to achieve this.
- You only need a pot and some measuring cups for the first method, but this method is the trickiest to get right.
- The second method uses the warming function of most modern rice cookers.
- The third method is the most reliable, but it requires a thermal circulator (sous vide machine).
- You can serve onsen tamago with soy sauce, but taking the time to make the dashi sauce will take your hot spring eggs to the next level.
Ingredients for Onsen Tamago
- Eggs - I used large eggs for this. If you use other sizes, you may need to adjust the times for Methods 1 and 2. I also recommend using the freshest eggs you can find, as these will have less loose albumen than older eggs.
- Dashi - Dashi is a Japanese stock made with katsuobushi(dried, smoked, and fermented skipjack tuna) and konbu (kelp). You can use dashi packs, or I have a dashi making tutorial you can follow.
- Soy sauce - Any Japanese dark soy sauce (such as Kikkoman) will work. Keep in mind that Chinese dark soy sauce is not the same as Japanese dark soy sauce.
- Salt - Using soy sauce alone to season the sauce will turn it dark brown. That's why I only use a little and then augment with salt.
- Sugar - The sugar balances out the sauce's saltiness and is not enough to make it obviously sweet.
- Garnish - I prefer my onsen tamago without a garnish, but it's not very pretty looking. If you want to make it present better, you can garnish it with some chopped scallions or mitsuba.
How to Make Onsen Tamago
Here are three different ways you can make onsen eggs at home. The first method requires the least special equipment but is the trickiest to get right. The third method requires a special machine, but it is the easiest and most reliable method.
Method 1: In a Pot
This method doesn't require any special equipment, but it's also the most finicky and may require experimentation to find the perfect timing for your setup. In my testing, slight differences in variables such as the temperature of the tap water, the temperature of the eggs, or the thickness of the pot can make a big difference in the time it takes to get a perfect onsen tamago. This method is also the most time-sensitive, as a five-minute difference in cooking time can mean the difference between a raw egg yolk and a mostly set yolk.
The key here is to use the heaviest pot you own, as it will retain heat the best. I also recommend using a thermometer to check the temperature of the water along the way for the most reliable results.
I start by adding 10 US cups of water to the pot and bringing it to a rolling boil on the stove with the lid on. Once the water is at a boil, turn off the heat and pour in 3 cups of tap water. This should bring the water temperature down to about 180°F. Next, add 5-8 cold eggs from the refrigerator, bringing the water temperature down to just under 170°F. Cover the pot with the lid and set the timer for 20 minutes.
Transfer the cooked eggs to a cold water bath to stop any carryover cooking.
Method 2: Rice Cooker
Most modern rice cookers have a "keep warm" mode that typically keeps the pot at around 160° F (71° C). This is still above the ideal temperature of 145° F (63° C), but because it's actively heated, you can start with water close to the target temperature after adding the eggs. Then, the temperature will slowly rise from there. This gives you a little more leeway in terms of time. Using this method, I've generally found that you can leave the eggs in from 20-30 minutes and still have it turn out okay.
As far as getting the water to the ideal temperature, I usually use 5 US cups of boiling water to 1 ½ cups of tap water. Once added to a cold rice cooker pot with 5 cold eggs straight from the fridge, the water should be right around the target temperature. Then you can turn on the keep warm function and set a timer for 25 minutes.
When the Onsen Tamago are done, transfer them to a cold water bath to stop any carryover cooking.
Method 3: Sous Vide Machine
This is hands down the safest and most reliable way of making Onsen Tamago. A sous vide machine, or thermal circulator, is basically a heater with a pump that holds a hot water bath at an exact temperature. This lets you cook food in the water bath to precisely the temperature you want. For Onsen Tamago I recommend setting the temperature to 145° F (63° C), adding in the eggs once the bath comes up to temperature, and then running the machine for 45 minutes. This will result in a custardy egg white with a yolk that's like cold honey.
Other Japanese Egg Recipes
Onsen Tamago (温泉卵) translates to hot spring egg, and it's a mouthwatering egg dish often served for breakfast at traditional Japanese inns called Ryokan. The low temperature of the water the eggs are cooked in causes the yolk to firm up without setting and gives the whites a silken texture that melts in your mouth. These slow-cooked eggs are usually served at room temperature with a savory dashi broth, giving them a flavor and texture similar to Chawanmushi.
Onsen Tamago is a 5-syllable name pronounced as follows (read the italicized parts).
on like tone
sen like senate
ta like tonic
ma like mall
go like ghost
Neutralizing pathogens in eggs is a matter of time and temperature. Higher temperatures will neutralize pathogens almost instantly, while lower temperatures take more time. The safest way to make Onsen Tamago is to use an immersion circulator (a.k.a. sous vide machine). That's because you can set the machine for the exact temperature you want the eggs to end up being at. Then you can cook the eggs for a period of time that's long enough to ensure the destruction of any microbes without overcooking the egg. Since both the pot method and rice cooker method involve hotter water than the target temperature, you have to pull the eggs out of the water bath as soon as they hit the desired internal temperature, or you'll end up with boiled eggs. Unfortunately, this also means there is a risk that the center of the yolk will not have maintained a safe temperature for long enough to fully pasteurize it. If you're concerned about this, you should use Method 3 to make your onsen tamago.
For hot spring eggs
- 5 eggs
- scallions (optional, chopped for garnish)
For dashi sauce
- ½ cup dashi
- 1 teaspoon soy sauce
- ½ teaspoon salt
- ½ teaspoon evaporated cane sugar
- Add 5 US cups of boiling water plus 1 ½ cups of tap water to a room temperature rice cooker.
- Add 5 eggs and close the lid. Turn on the rice cooker's warming function and set a timer for 20 minutes.
- While you wait for the hot spring eggs to cook, add the dashi, soy sauce, salt and sugar to a small saucepan and bring the mixture to a boil. Once the salt and sugar have dissolved, turn off the heat and let the sauce cool.
- Once the timer goes off, transfer the eggs to a cold water bath to stop the cooking.
- Crack the chilled eggs on a flat surface and gently break the Onsen Tamago into a small bowl. Serve drizzled with a small amount of dashi sauce and garnish with scallions.
Marc, thanks for showing these different methods and explaining the science behind onsen tamago! I’ve wanted to try them at home but haven’t gotten around to it. I combined the pot and rice cooker methods to adapt this for a small thermos jar instead. I used my electric kettle which has preset temperatures to start at 200, added two eggs, and let it set for 25 minutes. For a first try this worked out remarkably well! I will definitely experiment with this idea again 🙂
Marc Matsumoto says
You're welcome! Glad to hear you were able to get it to work in a thermos. 200°F might be a little hot (even after accounting for the temperature drop from the eggs), so if the eggs turned out firmer than expected you might want to lower the water temperature a bit with tap water.
Holy cow! I can't believe I nailed this on the first try (Made 12 eggs in 12 hours they were so good). I used the sous vide method, and I'm not sure I could have done it with the other methods nearly as neatly with my amateur skills. Of note, I have a pretty cheap sous vide model (Russell Hobbs with a heavy ceramic insert, no thermal circulation per se) but have zero complaints. Thanks a million, Marc. Those little details you highlight make all the difference... I think I'm going to leave my sous vide on all day from now on just for these!
Marc Matsumoto says
Hi DJ, I'm happy to hear you enjoyed this so much! My sous vide machine is from almost a decade ago, but I still use it regularly mainly for making onsen tamago😆
P.S. It's hard to resist using Tabasco or shichimi togarashi in lieu of the dashi sauce on occasion. I tend to reach for one of those red bottles for my morning eggs to wake me up, and the dashi sauce when I'm going for more serious presentation. Scallions/green onions/spring onions are really a huge boost: color, texture, contrasting flavor. Any other garnishes you might recommend to add a little variety (since I'm eating 4-6 a day!)? Nori flakes? A few minuscule pieces of anchovy? Diced kimchi?
Marc Matsumoto says
Hi DJ, sorry I missed this. Tabasco is a cool idea. Along those lines, how about some yuzu kosho https://norecipes.com/yuzu-kosho-yuzu-chili-paste/? Or maybe some furikake for a little extra texture https://norecipes.com/furikake-seasoning/?
Using the sous vide method, is is still necessary to put into a cold water bath afterwards?
Marc Matsumoto says
No, the cold water bath is to prevent carry over cooking. Since the sous vide method cooks the egg at exactly the right temperature there's no risk of going over that temperature.