The “masu” is a traditional, box-shaped sake cup typically made out of cypress or cedar. In use for centuries, it was originally a measuring cup for rice. A single masu measures 1 “go,” or a volume of 180 milliliters. Because it’s made of wood, it imparts a forest-like aroma and flavor to the sake inside. People often use it to drink “taru sake” (sake stored in wooden vats) to amplify the cedar flavor. You can also use it to drink “mokkiri” style by placing a glass inside and pouring sake so it overflows into the masu — a gesture of generosity and a mark of a good host.