Japan is a resourceful country with seemingly little natural resources to power the country. However, a closer look into how people lived in the past reveals a different story. Geothermal energy was used to warm the body via the onsen, and have been used in the onsen areas for cooking. Onsen cooking can still be seen in various onsen towns throughout Japan. Depending on the temperature, the food is steamed or boiled.
The cooking pool at Nozawa Onsen. The pool, which is near boiling point, is onsen water used especially for cooking.
For example, in Nozawa Onsen of the Nagano Prefecture, there are special pools of onsen water where the locals bring food in a basket or net. The basket is lowered into the pool to be boiled by the onsen water. The famous Nozawa-na and other vegetables are cooked this way.
In Beppu Onsen of Oita Prefecture, hot steam from the onsen known as the “Jigoku-gama” (translated as Hell’s Pot) are used to steam vegetables, fish, rice, and other ingredients.
The most famous product coming from the onsen cooking is the “Onsen Tamago” or boiled egg. This food can be found in almost any onsen town and is very distinct from your ordinary boiled egg as it is cooked in the onsen water. Crack open the egg and be surprised by the fact that the egg whites haven’t hardened. But the yolk is. It’s normal to have an hard egg white and an under-cooked yolk, but the opposite is true in the case of onsen tamago. This is because the egg is immersed in water of approx. 70°C for over an hour. The yolk usually hardens around 70°C and the egg whites harden around 80°C. Having the egg in the onsen water of around 70°C allows just the egg yolk to harden.
The “Jigoku-gama” (Hell’s pot) at Beppu Onsen. The steam from the onsen is used to steam the vegetables, fish, and rice
If you are in the Takayama area, the closest onsen is the Okuhida Onsen of Gifu Prefecture, about an hour drive from Takayama. The residents affectionately call this egg “Hantai-tamago” or reverse egg. Because of the salt content of the onsen, the egg itself has will have a slightly salty taste.
If you travel the onsen areas in Japan, we recommend that you search for the local onsen tamago and taste the different textures and tastes that each onsen will create from its different chemical composition and temperatures.