Bitters are made by macerating herbs and spices and infusing them in alcohol, generally a high ABV spirit. Once they’ve been macerated for long enough, the solids are strained. Bitters help accentuate flavour but they also bring their own flavour. The classic is Angostura (made from 90-odd herbs and spices but the recipe is a closely guarded secret) – it tastes very herbaceous and bitter; Peychaud’s bitters is quite minty in flavour – it is bitter but less so than Angostura; and it now has colouring in it to make it red. Bitters are added very sparingly to cocktails – I don’t generally add them to make things bitter; just to enhance flavour. Bitter cocktails come from their base spirit, such as Campari or a vermouth, not from adding bitters.