As explained in What is a Liqueur?, liqueurs combine a base spirit or “liquor” with various natural flavoring ingredients. Unless a specific base spirit is indicated, you can usually be safe in assuming that it is a neutral or grain-based spirit. The method of extraction depends on the ingredients being used.
There are three main ways to do this.
- Maceration: The ingredients are added to the alcohol itself, which extracts the essences from the ingredients. This is usually used for soft fruits like strawberries, raspberries, peaches, or bananas, for which distillation could be too harsh and alter the taste. Another form of this is infusion (or digestion), which is sometimes considered a different method, but in reality is a different version of the same method. Here, the ingredients are used very much like you would use them to make tea. They are soaked, or steeped, in water until they are soft. They are then covered with a heated base spirit, which takes on the flavor of the tea.
- Percolation: The base spirit is percolated or dripped through the flavoring ingredients so that the essences are extracted and is a lot like brewing a pot of coffee, just as it sounds. The base spirit is put in the bottom of a tank and heated. It is then pumped upwards to be sprayed over the flavor ingredients at the top of the tank. The alcohol becomes infused with the flavor essences as it drips back down to the bottom of the tank. This repeats over and over until as much flavor as possible has been extracted from the ingredients.
- Distillation: The ingredients are mixed with alcohol, and then everything is distilled together. The purpose is not to extract the alcohol, as when the spirit is originally distilled, but to extract aromatic elements from the ingredients. This is especially suited to dried agents like flowers, plants, seeds, or rinds.
After flavoring, the liqueurs are sweetened. Some are less sweet than others, which may be very sweet or even syrupy. In the U.S. the sweetness is regulated and has been since 1936: A liqueur must be at least 2.5 percent sugar, which is actually pretty low on the sweet scale for a liqueur, and so fairly rare. Some people seem to think this is why American brands of “schnapps” are so sweet compared to true German Schnapps, but this has no bearing, as 2.5% is a drop in the bucket next to the cloying sweetness of some of these products. To put this into perspective, just imagine that you had 100 cups of a spirit, and only added 2.5 cups of sugar. Would this be very sweet?
See also Homemade Coffee Liqueur (Like Kahlúa)