Mirin is a staple of Japanese kitchens, yet few people know what it actually is.
Although these days it's thought of solely as a cooking ingredient, mirin was originally regarded as an expensive, high-class beverage. It was the tipple of choice of wealthy ladies, who mixed it with shōchū (distilled spirits) to produce a sweet, heady drink.
Mirin is made by fermenting steamed mochi or short-grain rice with rice kōji (rice malt), and then mixing it with shōchū and letting it mature for 40 to 60 days. The starches in the rice break down into maltose, a type of complex sugar. The mixture then is filtered to produce a golden, sweet, almost syrupy concoction that is reminiscent of Marsala, cream sherry and other sweet fortified wines.