Red bean jam (“anko” or “an”) is a common ingredient in traditional Japanese sweets. Sweet red beans (azuki) are cooked and kneaded with a lot of sugar to make a thick paste. There are 2 varieties: koshian (smooth) and tsubuan (some whole beans in it).
Traditionally, anko has been mainly used in manju, the most famous Japanese sweet. Bean paste is wrapped in soft dough made of flour, rice powder and buckwheat, which is often flavored with green tea. It was introduced to Japan by a Chinese merchant in 1341. Since then, its sweet simplicity has made it a staple of the Japanese diet.
Recently, the popularity of manju has been eclipsed by anpan, a bread roll filled with sweet bean jam. The multicultural snack was invented by Yasubei Kimura, an unemployed samurai. Japan was beginning to adopt Western foods, but they only bread they could make was salty and sour. Kimura used bean jam to make bread palatable for Japanese tastes.
In 1875, the Emperor Meiji was presented with anpan, painstakingly decorated with pickled cherry blossoms. He was so impressed he requested that the sweet be served to him every day. Following his endorsement, the popularity of anpan (and bread in general) spread rapidly throughout Japan.