
Tonka bitters are a cocktail bitters, a high-proof botanical infusion whose defining aromatic is the tonka bean, dosed in dashes to flavour drinks.
A lingering coumarin-led finish carries vanilla and almond over hints of cherry and cinnamon, all delivered at concentrated seasoning strength.
Bartenders add it a dash or two at a time, as an aromatic accent that sets a drink's top-note rather than a base or modifier by volume; it also contributes a minor bittering edge.
Hard to replace on the defining aroma: only bitters or extracts from tonka bean, or a coumarin-rich analogue such as sweet woodruff, approach the vanilla/almond/cherry note, and none match it exactly; the minor bittering alone can be covered by any aromatic bitters.
Aromatic bitters
Tonka bitters are defined by the specific tonka-bean coumarin aroma of vanilla, almond and cherry, whereas generic aromatic bitters lead with clove, cinnamon and gentian-type spice and bittering.
Aromatic botanicals are macerated in a high-proof alcohol base to yield a concentrated flavouring, with the characteristic note coming from the tonka bean, the seed of the South American tree Dipteryx odorata. That seed is dominated by coumarin, a compound banned as a food additive in the United States, which constrains the availability and legal food use of tonka-flavoured products there.