The origin of Amazake can be traced back to Kofun period (250 to 538 AD). Let's learn the history of Amazake.

Nara period (710-794 AD) 

Nihon Shoki (日本書記), the second-oldest book of classical Japanese history which stated that the Konohanasakuya-hime (木花咲耶姫) "[cherry] tree blossom blooming princess" created "Ama no Tamuzake" which is considered to be the origin of modern Amazake.

Heian Period (794 - 1185 AD) 

Amazake was called "Kosake (醴酒)" in the Engishiki (延喜式).  Engishiki is a Japanese book about laws and customs
which was enforced in the year 967.

Also Amazake was commonly enjoyed by the nobles during this period.

Muromachi Period (1336 - 1573 AD)

"Kosake" (醴酒)" was mentioned in a June event in Kuji Kongen, a book on ancient practices and precedents of the imperial court written by Kaneyoshi Ichijo.

Amazake was taken as a fatigue recovery drink in the hot summer months due to its powerful nutritional benefits among the public. This was mentioned on Morisada Mankou (守貞漫稿), a kind of encyclopedia during the Edo period. This was drafted by Kitagawa Morisada in1838. 

Amazake sellers (amazake-uri) carried their Amazake products suspended from each end of a shoulder pole as they sold their goods in their neighborhoods.

Current

Amazake is very popular in Japan nowadays because of its health and beauty benefits, and is known in Japan as an "I.V. drink" for all ages.