The bitter from gentian root, used across Campari, Aperol, sweet vermouth, Angostura, and most amari. Bitter compounds activate TAS2R taste receptors that evolved to detect plant alkaloids. The same machinery that makes broccoli taste bad to children also makes a Negroni taste like an adult ordered it.
Bourbon's fingerprint, extracted from the charred American oak the law requires for aging. Same molecule as the vanilla bean's signature, so a well-aged bourbon legitimately tastes like vanilla. Chemistry, not metaphor. Cognac, aged rum, tequila reposado all extract vanillin from oak too. Different barrels, same molecule.
Lemon's defining note: technically a mix of two geometric isomers (geranial and neral) that read as the same aroma to the nose. Lemon peel, lemongrass, lemon verbena, and Indian chai all carry it. In cocktails it's what a lemon twist contributes that lemon juice can't: the volatile expressed from the oil glands, not the acid from the pulp.
Angostura bitters as the base spirit, unheard of until 2008: an ounce and a half of a liquid normally measured in dashes. Gentiopicroside loads up to receptor-saturation levels, and orgeat's benzaldehyde from almond and rose water from the back match it for depth. Angostura is 44% ABV on its own, so the bitters carry the strength.
PROVENANCE
Giuseppe Gonzalez created the Trinidad Sour at the Clover Club in Brooklyn in 2009 as a deliberate provocation: Angostura bitters used as the base spirit rather than a half-dash modifier. Trinidad refers to the bitters' origin (Angostura is made in Trinidad). The drink launched a generation of bartender experiments with overproof bitters and herbal liqueurs in non-traditional roles. The orgeat-almond-rose-water combination is what makes it drinkable; without it, an ounce and a half of bitters reads as medicinal.