The eggs were supposed to have been created by the restaurateur Huang Zhangnian (黃張哖) serving snacks to the dock hands in the sea-side town. On one rainy day with less business than usual, Huang Zhangnian had to continually recook red cooked eggs (滷蛋) to keep them warm after taking them out of the soy sauce broth. The recooking and drying process eventually resulted in eggs that were dark, flavourful, and chewy, which was extremely popular with the locals. Huang eventually founded a new business based on her iron egg recipe, selling them under the brand Apotiedan (Chinese: 阿婆鐵蛋; literally: "Grandma's iron eggs"). They can only be created by the use of "chicken, pigeon or quail eggs." They are unlike black eggs because they are unable to be made from duck eggs. The popularity of iron eggs has risen and they can be found in other countries besides Taiwan, such as in Africa and the Middle East.
The dish consists of small eggs that have been repeatedly stewed in a mix of spices and air-dried. The resulting eggs are dark brown on the outside, chewy in texture, and very flavourful compared to standard boiled eggs. It has been said to taste "sweet, spicy and slightly salty with a concentrated egg flavour - a great snack with drinks."