The hassaku is a large, firm, pleasantly bitter Japanese citrus — a natural pomelo hybrid the size of a small grapefruit, eaten segment by segment rather than juiced. Under a thick, knobbly pale-yellow to orange rind sit big, coarse-jacketed segments whose flesh is crisp and separates into distinct juice sacs, tasting fresh, lightly sweet and bracingly bitter with a clean, slightly sour edge — a springtime eating citrus prized in Japan for its firm bite and refreshing bitterness rather than for sweetness.