Wikipedia Article About Mirin on Wikipedia
Mirin (kanji: 味醂; hiragana: みりん) is an essential condiment used in Japanese cuisine, with a slightly sweet taste. It is a kind of rice wine similar to sake, but with a lower alcohol content. In the Edo period, Mirin was drunk as a sweet sake. お屠蘇 【おとそ】 Otoso that is drank on Shōgatsu (正月, the Japanese New Year) is made by soaking a spice mixture in mirin. Nowadays premium sake is often drunk instead.
In the Kansai style of cooking, mirin should be used after a quick boiling to let alcohol evaporate while in Kanto style of cooking, mirin should be used as-is. Boiled mirin is called nikiri mirin, literally "boiled over Mirin."