Kabosu (Citrus sphaerocarpa) is a round, deep-green Japanese citrus picked while still unripe and valued almost entirely for its mild, fragrant, sour juice rather than its flesh. A speciality of Ōita Prefecture on the island of Kyushu, it is squeezed over grilled fish, fugu, hot-pot dishes and sashimi, stirred into ponzu and dressings, and splashed into shōchū — bringing a softer, rounder, less aggressive acidity than lemon or lime, with a gentle floral-citrus perfume.