What the mouth remembers after swallowing — the lingering finish that colours the whole impression of a food or drink. It may be pleasant, like the cocoa bloom of good chocolate or the caramel tail of well-roasted coffee, or unwelcome: rancid, metallic or bitter persistence that betrays oxidation, contamination or over-extraction. Sensory panels time and profile aftertaste because it drives liking more than the first bite suggests, and sweetener developers live or die by it — a clean finish versus lingering liquorice or metallic notes decides formulations. Aftertaste is flavour’s echo, and echoes linger.