In the world of food, one palate’s trash really is another’s treasure. Take the case of the egg, for instance. In most Western dishes, eggs are treated like delicate proteins, cooked for no longer than 10 minutes or so. In China, however, eggs are cured and boiled for days or weeks, turning the rich, golden yolk into a sulfurous, fermented mass. You may prefer your eggs scrambled or over easy, but to many, a perfectly aged egg is a delicious treat.

Thousand-year eggs take this custom to the extreme. Though they’re also known as century eggs, preserved eggs and millennium eggs, these terms are all misnomers: the eggs are only cured for about 100 days. According to legend, the tradition was born more than 600 years ago, when a man in Hunan Province discovered a cache of duck eggs buried under slaked lime in his yard. The adventurous man tasted the eggs and enjoyed them enough to make his own batch, this time adding salt and tea for flavor.

A thousand-year egg looks very different from its freshly hatched counterparts, with the white resembling glossy, amber Jell-O. Etched into the eggs shell are snowflake-like patterns created by fungi. The yolk is a hard ball, colored dark gray or green. Thousand-year eggs are typically sliced and served alongside soft tofu or congee porridge, or on their own with pickled ginger root.

But how do they taste? The uninitiated might find it hard to get past thousand-year eggs’ ammonia odor, caused by the reaction of its natural chemicals during the curing process. The scent can range from no worse than a fine French cheese to a pungent, room-emptying stench. The actual flavor is sharp, astringent and slightly mineral. Some say you can taste slight differences in the eggs depending on the clay or tea used in the preserving process. They’re often compared to a rich cheese—but that may be because no commonly eaten food in the Western tradition bears any resemblance to a thousand-year egg.