The special drink is a byproduct of cellophane noodle production. It is slightly sour with a pungent egg-like smell. Beijing has a long history of making this juice. As early as in the Liao (907-1125 AD) and Song (960-1279 AD) dynasties, mung bean juice was very popular. Beijing locals love to drink the juice as it is rich in protein, vitamin C and rough fiber and helps drive away that summer heat, invigorate the function of the spleen and stimulate the appetite.