Tea eggs are simply hard-boiled that have been further stewed in a salted tea liquid. Other flavourings such as soy sauce and Chinese five-spice powder are often added as well. The eggs are actually boiled twice. After the first boiling, when the insides are hardened, the shell of each egg is lightly cracked. The eggs are then boiled for much longer duration in the black tea mixture for a second time, which allows the flavour of the tea to penetrate deep into the egg. The dark colour of the tea also stains through the cracks of the eggs creating a pattern on the peeled eggs that resembles the crazing of some ceramic glaze surfaces.
Appearance and Flavor
In the end, when the peel comes off, you should see regions of light and dark brown, with mid-brownish tone along the cracks of the peel. The yolk should have a thin greyish layer with the core being the usual yellow. As for flavor, it really depends on what tea you use and your variation of spices. Five-spice powder adds a savory, slightly salty tone to the white, and the tea should bring out the yolk's flavor.
The tea used in making tea eggs are usually low in quality but high in dark-brown tannins. Green tea is considered too bitter for the use of making tea eggs. In Hong Kong Pu-erh tea is most commonly used, but it can be substituted with black tea.
In Northeast China tea eggs are often privately made and sold. One might also see street vendors cooking and selling steaming-hot tea eggs. In Shanghai, tea eggs are sold by both convenience stores and private street vendors, where the tea eggs are often cooked together with dried tofu.
In Taiwan, tea eggs are a fixture of convenience stores. Through 7-Eleven chains alone, an average of 40 million tea eggs are sold per year.