What are bitters?
Bitters are complex flavor extracts that are extracted and preserved by alcohol. They are not considered alcoholic beverage, but rather a flavor contributor since the quantity is so minuscule.
Bitters are potent, complex flavor extracts from plants, extracted and stabilized by alcohol, to elevate drinks and food. Plants and alcohol. As they are very concentrated and used in such sparring quantity (dashes or as we call them since we use sleeved dropper bottles, sleeves) they don't contribute alcohol to a drink, rather the alcohol is there to extract and stabilize the plants.
We know them in American culture mainly for their essential role in the mixed drink known as the cocktail.
A cocktail by classic definition is very specific. It is a drink containing the balanced flavors of a spirit (whiskey, rum, tequila, etc), a sweetener (cane, maple syrup, etc), a bitter, and a diluter (water in the form of ice, etc).
Although recently we know them for making Old Fashioneds, well... Old Fashioned... they have been utilized for centuries to aid digestion, calm inflammation, boost circulation, and many other immune system happenings that can be attended to by plant extracts.
Bitters are like the vanilla extract added to a batch of cookies; flavor essences extracted by alcohol. The alcohol we use for bitters we make from scratch from rye and cane, which certainly sets us apart from the pack.
Bitters contribute balance to sweetness in cocktails and food, exactly like hops do in beer or spices and salt do in a dish.
Instead of just one ingredient, like vanilla extract, they are packed with barks, roots, herbs, and fruits/fruit peels. Botanicals of any persuasion, the sky is the limit. Aromatic bitters of some kind are an essential player in any cocktail. By definition, a cocktail is a type of mixed drink containing spirits of any kind, sugar, water, and bitters. Without bitters, this drink becomes another type of mixed drink.
They also taste great on their own in a soda, iced coffee, and can even add great depth to a meal or dessert.
Note that while bitters are high in alcohol, the government classifies them as "non-potable" alcohol because they are additions (dashes) to drinks and dishes, rather than an actual bottle of booze. Therefore it is legal to directly sell these online, and at say, a coffee shop. No liquor license needed.