When you visit Japanese onsen, you may come across places where they cook eggs in the hot spring water.
They are called Onsen Tamago (温泉卵 Hot spring eggs).
Image source: irasally
Traditionally, the raw eggs are placed inside the basket or net and left to be cooked slowly in the onsen. They are cooked in the hot spring water of approximately 70°C (158ºF) for 30 to 40 minutes. This is because egg yolk solidifies at around 70°C while egg white solidifies at around 80°C.
The main characteristic of onsen tamago is that the egg white is softer than the egg yolk. So it has a unique texture, egg white is very milky and soft, while the egg yolk is slightly firm but still has the creamy texture. Onsen tamago is often served with broth and soy sauce in a small bowl.
Most Japanese ryokan in onsen areas serve onsen tamago as a part of breakfast.
Cooking the eggs!
So if you are curious to try some onsen tamago, here are some Japanese ryokan that lets you make your own!
1. Kounso【光雲荘】 (Tochigi prefecture)
At Kounso, you can make your own onsen tamago while having a foot bath.
You can even have some sake while you wait too.
2. Nakajimaya (Nagano prefecture)
Small Japanese inn. You can either make your own onsen tamago or if you are feeling lazy, you can just buy some from their shop!
They'll give you some eggs in the kitchen, place them in onsen.
Eggs will be cooked while you are in the onsen (note: not in the same water!) They have a separate onsen for eggs.