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Fuji-Hakone-Izu NP, Kanagawa
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A 2023 study found little iron sulfide in the egg’s thin black film; it is rich in carbon, nitrogen, sulfur and protein-like material. Heat-driven browning may form it, while air gradually fades the black toward brown.
Each egg spends about 60 minutes in an 80°C hot-water pool, then 15 minutes in 100°C steam to finish cooking. A dedicated little ropeway carries the finished eggs down to the shop.
The black-shell version reportedly began by chance around 1950: eggs cooked in Owakudani’s hot-spring pool came out black. Sellers were surprised, liked the taste, and began selling the unusual eggs.
The tale that an egg adds 7 years to your life is linked to Owakudani’s Enmei Jizō, a long-life and child-protection statue said to have been carved by Kōbō Daishi. The lucky 7 came later; it’s folklore, not a promise.
In a 2013 TV taste-sensor test, the egg white was saltier and the yolk registered more umami than water-boiled eggs cooked the same way. The suggested reason: hot-spring minerals pass through the shell.
Owakudani sold hot-spring eggs to tourists and sulfur miners before the shells turned black. Early sellers steamed them in bamboo baskets inside pipes set in fumarole ground; eggs came from Gotemba farms, carried on backs or by horse.
The maker says black eggs are sold warm on the day they’re made. Leftovers are now reused instead of simply discarded, becoming smoked eggs or furikake—a savory rice seasoning.
