Bitters

Highly concentrated botanical extracts — herbs, roots, bark and citrus peel infused into high-proof alcohol. They're used by the dash to add depth and aroma. Think of them as the salt and pepper of the bar.

A dash or two, rarely more. An Old Fashioned takes 2–3 dashes of Angostura. Too much and the drink turns medicinal — bitters are seasoning, not an ingredient you pour.

Practically never. The high alcohol content preserves them for years, so a bottle will almost certainly outlast your interest in it. Store upright in a cupboard.

Angostura aromatic covers the most ground — Old Fashioneds, Manhattans, Sazeracs. Add orange bitters for gin and whiskey drinks. Those two build most of the classics.