Bitters

Angostura appears in the Old Fashioned, the Manhattan, the Champagne Cocktail, the Pisco Sour - where Amargo is the Peruvian original and Angostura the usual stand-in - and a dozen others. It usually gets listed beside the Tabasco and the Worcestershire sauce, and nobody says what it is. So: bitters are a high-proof spirit infused with bark, root, and aromatic botanicals to the point of being undrinkable on their own, used in dashes. The bitterness itself usually comes from gentian root, from wormwood, or from quinine - the same quinine that makes tonic bitter.

They exist because bitterness is a structural element, not a flavour. Sweet and sour can balance each other into something flat and sickly sweet; a few dashes of bitters give the drink an edge and pull the other elements into focus. The usual analogy is salt in cooking, and it's a good one - you don't taste it as itself, you notice its absence.

• Aromatic - Angostura is the reference. Clove, cinnamon, gentian. If a recipe just says "bitters", it means this.
• Orange - brighter and citrus-led. Lifts gin and lightens a Manhattan.
• Peychaud's - from New Orleans, lighter and anise-forward, faintly floral. The Sazerac needs it specifically.
• Everything else - celery, cardamom, chocolate, grapefruit. Useful once the first three are on the shelf, not before.

A bottle of Angostura lasts for years - it's roughly 45% alcohol and used a few drops at a time. The distinctive oversized paper label is said to be a mistake nobody ever corrected, though that is the company's own account and more than one version of it is in circulation.