Uirou is a Japanese steamed sweets, made from flour and sugar. It is made by pouring the batter in a mould, and cooked in a steamer. There are several different kinds of flour or starch used, such as rice flour, wheat flour, and bracken starch. Either white sugar or brown sugar is used. Sometimes ingredients like as azuki red bean paste or matcha green tea are added.
The standard uirou is believed to come from Muromachi period (1336-1573), which used brown sugar. However, there are three theories of the origin of uirou. One is that in the Edo period (1603-1867), there was a medicine called uirou which was black color, and the sweets which is similar color started to be called uirou too.
The second is said to be derived from the sweets nama-senbei, which comes from the Mikawa area of Aichi prefecture. Nama means raw, and senbei means rice cracker, but the sweets was rather soft and sticky than dry and crunchy.
The third is believed to come from a sweets which was offered to warlord Ashikaga Yoshimitsu by a Chinese who exiled to Hakata in Kyushu, southern part of Japan, when he entered Kyoto by the order of Yoshimitsu. The sweets was served to take away the after taste of the medicine uirou, and the sweets itself started to be called uirou.
Uirou from Nagoya city, Aichi prefecture is very famous, and uirou made by the company Aoyanagi-sohonke, founded in 1879 in Nagoya, has the highest sales among all other companies that produces uirou. In 1931, uirou was started to be sold on the platform at Nagoya railway station. In 1964, uirou was widely sold on Tokaido shinkansen bullet train, and spread across the nation.