“O-Zenzai” and “O-Shiruko” are both commonly known as Wa-sweets made of warm red bean paste (mainly azuki bean paste) soup with rice cakes, shiratama dumplings, monaka-dane, sweetened chestnuts, etc. The difference is that “O-Zenzai” is made with Tsubu-an, while “O-Shiruko” is made with Koshi-an. Red bean soup has been eaten for a relatively long time, mainly by the upper class people. It is thought that it was after the Edo period (1603-1868) that red bean paste came to be eaten by the general public as sweets (or an ingredient in sweets). It is said that it was around the time that the current “O-Zenzai” and “O-Shiruko” were created.
However, there are many theories about the difference between “O-Zenzai”/”O-Shiruko” and how to distinguish them… Strictly speaking, it’s a bit complicated, as the theories differ between Kanto and Kansai reagions. Originally, in the Kanto region, the name “Zenzai” was used to refer to red bean paste without any liquidity. And the soup with red bean paste is called “Shiruko”. In the both, there was no difference in the name due to the difference between Tsubu-an or Koshi-an. But, in the Kansai reion, the name “Zenzai” was used to refer to all kinds of hot soup made with Tsubu-an. And those made with Koshi-an were called “Shiruko”. So which is the original, the Kanto style or the Kansai style? There are also many theories, and it’s not very clear… Occasionally, due to this kind of misrecognition, you may get something different from what you expected to order. If this should happen, please do not get angry and remind this learned…(￣▽￣;) As a matter of fact, “I” have experienced it myself…
Generally, both “O-Zenzai” and “O-Shiruko” are served as warm sweets, but in summer, they are also served as cold sweets. In those cases, they are often clearly labeled as “冷やし(cold-○○)”.
※ Some of the canned “O-Shiruko” may have azuki grains in it, some may not, but we guess it is the Kanto style.