Amazake

 is a traditional sweet, low-alcohol Japanese drink made from fermented rice. "Amazake" dates from the Kofun period, and it is mentioned in the Nihon Shoki. It is part of the family of traditional Japanese foods made using the koji mold , which also includes miso, soy sauce, and sake.
There are several recipes for "amazake" that have been used for hundreds of years. By a popular recipe, "kōji" is added to cooled whole grain rice causing enzymes to break down the carbohydrates into simpler unrefined sugars. As the mixture incubates, sweetness develops naturally. By another popular recipe, sake kasu is simply mixed with water, but usually sugar is added.
"Amazake" can be used as a dessert, snack, natural sweetening agent, baby food, salad dressing or smoothie. The traditional drink (prepared by combining "amazake" and water, heated to a simmer, and often topped with a pinch of finely grated ginger) was popular with street vendors, and it is still served at inns, teahouses, and at festivals. Many Shinto shrines provide or sell it in the New Year. In the 20th century, an instant version became available.
"Amazake" is believed to be very nutritious. It contains vitamin B1, B2, B6, folic acid, dietary fiber, oligosaccharide, cysteine, arginine and glutamine. It is often considered a hangover cure in Japan. Outside Japan, it is often sold in Asian grocery stores during the winter months, and, all year round, in natural food stores in the U.S. and Europe, as a beverage and natural sweetener.
Similar beverages include the Chinese "jiuniang" and Korean "gamju". In grape winemaking, must – sweet, thick, unfermented grape juice – is a similar product.