From the brewery:

Rainbock is a Maibock-style beer, brewed as a celebration of spring and for new beginnings, much like a rainbow after a storm. Brewed in the depths of winter and lagered for months at near-freezing temperatures, Rainbock emerges from its hibernation rich, mellow and surprisingly nimble. Brewed using a traditional double-decoction mash, and hopped with British-grown Akoya and Godiva hops, enjoy responsibly.