Bitters are an alcoholic beverage that is made with herbs, spices, and fruits. It has a bitter or bittersweet flavor to it. A little bit of this stuff goes a long way. It is not meant to be drunk by itself. Traditionally, bitters came in two varieties; regular or orange. However, recently bitters are being produced in a wide variety of flavors. Many brands of bitters have been coming out recently, but Angostura is the oldest and by far the most common brand. To stay true to the recipes you will want to use regular Angostura bitters, unless otherwise specified. That being said it is fun to experiment with the different varieties of bitters.