A balut is a fertilized duck (or chicken) egg with a nearly-developed embryo inside that is boiled and eaten in the shell.
Popularly believed to be an aphrodisiac and considered a high-protein, hearty snack, balut are mostly sold by street vendors in the regions where they are available. It is commonly sold as streetfood in the Philippines.
Duck eggs that are not properly developed after nine to twelve days are sold as penoy, which look, smell and taste similar to a regular hard-boiled egg. In Filipino cuisine, these are occasionally beaten and fried, similar to scrambled eggs, and served with a vinegar dip.
The age of the egg before it can be cooked is a matter of local preference. In the Philippines, the ideal balut is 17 days old, at which point it is said to be balut sa puti ("wrapped in white"). The chick inside is not old enough to show its beak, feathers or claws and the bones are undeveloped. The Vietnamese often prefer their balut mature from 19 days up to 21 days, when the chick is old enough to be recognizable as a baby duck and has bones that will be firm but tender when cooked. In Cambodia, it is eaten while it is still warm in its shell. It is served with nothing more than a little garnish, which is usually a mixture of lime juice and ground pepper