Flavido is the same substance as zest — the coloured outer layer of citrus peel, and by extension the term for that aromatic outer skin. The flavedo (the alternate spelling) holds the oil glands that give citrus its perfume: the limonene and citral that burst from a twisted lemon peel over a cocktail. Beneath it lies the albedo, the bitter white pith — and the cook’s skill is taking the flavido without the albedo, the fragrance without the bitterness. Zest flavours cakes, cures, marinades, and liqueurs; candied, it becomes a confection. The word is the technician’s term for what every cook knows by hand: the thin, coloured, fragrant skin of the citrus fruit, where the flavour lives.