Hops

The cone-shaped flowers of the climbing plant Humulus lupulus, the defining flavour ingredient of beer. They contribute bitterness, aroma, and flavour, and their resins also help stabilize foam and inhibit certain spoilage bacteria. Varieties are selected for their alpha-acid content and aromatic oils, and they are used as whole cones, pellets, or extracts. Beyond bitterness, hops are a preservative in the traditional sense — their antibacterial properties helped keep beer sound long before refrigeration — and breeding programmes continue to produce varieties with novel aroma profiles for craft and mainstream brewing alike.