The term "mirin" is difficult to translate. It is, for example. often called "sweet cooking sake", but that is wrong. Mirin does not contain any sake and has not been fermented either.
Mirin is produced by mixing steamed glutinous rice (the type used for mochi rice cakes) on which the koji mold has been cultivated, with shochu (Japanese distilled liquor). Instead of shochu it is also possible to use brewer's alcohol. The koji transforms the starch in the rice into glucose and over a period of 40 to 60 days a delicious sweetness develops. When the mirin is ready, it contains 13.5 to 14.5% alcohol and 40 to 50% sugar. The alcohol will evaporate during cooking.
There are several cheap "chemical" replacements on the market, so to make clear we have to do with real mirin, it is usually called "hon-mirin." You can also recognize it by the alcohol percentage of around 14% that is always on the bottle, and the light brown color, as a thin, golden syrup. The chemical replacements are lighter colored and contain less than 1% alcohol.
Mirin possesses a refined sweet taste and a delicious aroma. It also contains lots of umami and is therefore a much more refined sweetener than ordinary sugar.
Mirin is also used as ingredient for all kinds of dip sauces for noodles, for sweetening simmered dishes, for marinades, and the sauces for kabayaki and teriyaki, as well as for glazing grilled foods. Mirin also helps to mask the strong aromas of meat or fish.
In the past, mirin was sometimes also consumed as an alcoholic drink, by adding more shochu. It is still used as ingredient in otoso, the New Year's sake that has been spiced up with a herb mixture.