Yunomine Onsen — photo: Nekosuki · CC BY-SA 4.0 · Wikimedia Commons
Onsen eggs: what onsen tamago is, and where the hot spring cooks them
"Onsen egg" means two different things in Japan. One is a dish: a soft egg, cooked slowly below boiling, that turns up at almost every ryokan breakfast. The other is a place: a pool or a steam vent so hot that the town cooks eggs in it, and you can buy one, or drop your own in. This guide explains the first and tells you where to find the second, using the source temperatures in our records.
The short answer
- Onsen tamago 温泉卵 is a style of egg, not an egg from a spring. The yolk is set and creamy, the white is soft and loose. It is served cold or warm in a little dashi and soy sauce.
- Black eggs 黒たまご (kuro-tamago) are hard-boiled eggs from Ōwakudani in Hakone. The shell is black; the inside is an ordinary boiled egg.
- Cook it yourself at the boiling pools of Yunomine and Yumura, or in the steam kitchen of Kannawa in Beppu.
- Watch, don't touch at Nozawa's Ogama, which is the villagers' kitchen.
What onsen tamago is
An egg yolk sets at a lower temperature than most of the white. Hold an egg in water a little below 70 °C for about half an hour and you get the reverse of a soft-boiled egg: a yolk that is firm enough to hold its shape, inside a white that is still runny. That is onsen tamago. The name comes from hot springs whose water sits around that temperature, where an egg left in the overflow would cook this way by itself.
Today most onsen tamago are made in a kitchen, not in a spring. At a ryokan you will usually find one at breakfast, cracked into a small bowl with a spoonful of dashi, soy sauce and sometimes a little green onion. Eat it with a spoon, or tip it over your rice. It also shows up on top of udon, gyudon and ramen far from any spring. See what a ryokan dinner and breakfast are like for the rest of the tray.
It is a soft-cooked egg. If you avoid soft or runny eggs at home, treat it the same way here and ask for something else; the boiled and steamed eggs sold at the springs below are cooked through.
Why only some towns can do this
Cooking with the spring needs water or steam far hotter than anything you would bathe in, and that is rarer than it sounds. Of the 1,167 onsen areas in our records with a source temperature, 78 record 80 °C or more, 42 record more than 90 °C, and only 22 reach 98 °C. Most of Japan's springs are warm, not boiling. The towns that cook with their water are the ones on that short list, and you go to them on purpose.
Hakone: the black eggs of Ōwakudani
Ōwakudani is the steaming volcanic valley above Hakone, on the ropeway between Sōunzan and Lake Ashi. The eggs are boiled in a hot pool there, at around 80 °C, for about an hour. Iron from the water sticks to the porous shell and reacts with hydrogen sulfide, the gas behind the rotten-egg smell, which turns the shell black. They are then steamed to finish. Peel one and it is a plain hard-boiled egg.
They are sold in bags at the shop in the valley. The local saying is that each one adds seven years to your life; it is a saying. You cannot cook your own here, and you cannot walk to the pools. Ōwakudani is an active volcanic area, and access is sometimes limited when the alert level rises, so check the ropeway's notices on the day. The Hakone guide covers the valley and why the milky water in many Hakone inns is made there.
Yunomine: the yuzutsu
Yunomine Onsen in Wakayama is a small town along a stream on the Kumano Kodō. Its source is recorded at 92 °C. At the head of the stream is the 湯筒 (yuzutsu), a pool where the water comes up boiling. People lower raw eggs and vegetables into it in net bags and lift them out when they are done; the shops beside it sell eggs and bags for it. How long to leave them depends on what you want, so ask at the shop. Keep your hands out of the pool. See the Yunomine guide.
Yumura: the Arayu
Yumura Onsen in northern Hyōgo has a single source recorded at 98 °C, pouring out 470 litres a minute, with 24 inns on record. Where it comes up, at the 荒湯 (Arayu), there is a basin for boiling eggs. Eggs are sold nearby, and the spot is open at all hours. At this temperature every bath in town has to be cooled or diluted, which is why you can cook in it and not sit in it. Yumura pairs with Kinosaki for a second night.
Beppu: steaming in Kannawa
Kannawa Onsen, in the north of Beppu, records 100 °C, and steam comes up through the streets. Its public steam kitchen lets you cook with it, a style called 地獄蒸し (jigoku-mushi), "hell steaming". You buy a ticket for a steamer from a machine, pick up eggs, vegetables or seafood, put them in a basket in the vent, and set a timer. No booking is taken; on busy days you wait for a free steamer. Lift the lid slowly and stand back: the steam burns. It closes one day a month, so check before you go.
Unzen: eggs from the hells
In Unzen, Nagasaki, the steaming ground at the centre of town is called the hells. A pipe carries steam to a small shop by the path, which sells eggs cooked in it, as it has for more than a century. There is a foot-steaming spot next to it. The cats there know about the eggs.
Places that cook, but not for you
- Nozawa. Nozawa Onsen records sources up to 90 °C. At the top of the village, the stone pools of 麻釜 (Ogama) are where villagers boil vegetables, eggs and nozawana greens. It is a working kitchen. Look from the path. See the Nozawa guide.
- Tsuetate and Obama. Tsuetate in Kumamoto records 100 °C and the town steams food in its vents; Obama on the coast below Unzen records 105 °C, the highest figure in our data. See the Kyushu guide.
In most other towns, including famous ones, "onsen egg" on a sign means onsen tamago made in a pan. That is still a good egg. It just is not a sight.
Onsen manjū
The other food every onsen town sells is 温泉まんじゅう (onsen manjū), small steamed buns filled with sweet bean paste, usually brown on the outside. They are sold by the box near the station and on the main street, made fresh in the morning. Ikaho in Gunma is one of the towns that claims to have started them. They are a souvenir and a snack, not something cooked in the spring.
A few practical points
- Eat them the same day. Eggs from the springs are sold to eat on the spot or that day. If you want something to carry home, buy the boxed sweets.
- Mind the water. The pools you cook in are 90 °C or hotter. Hold children back and keep your hands out, even if you see locals at work there.
- Bring a little cash. Egg stalls and steam kitchens are small operations.
- Don't expect the egg smell in the egg. The smell at Ōwakudani and other volcanic places is hydrogen sulfide from the ground. See the sulfur guide.
How we put this together
Search suggestions in English ran to about 60 phrases on onsen eggs, from "is onsen egg cooked" and "what is onsen tamago" to "hakone onsen black egg", "kusatsu onsen egg" and "yunomine onsen eggs". We checked each cooking spot against local tourism listings, and took the source temperatures, flow and inn numbers from our own records. Opening times and rules at the cooking spots change, so treat them as a guide and check on the day.
Planning the trip around the food? Read ryokan meals first. New to onsen? See onsen etiquette and planning your first onsen trip.