The most common technique for floating or layering an ingredient is to pour it slowly over the back of a spoon. This disperses the liquid over a wider surface, allowing it to float instead of sinking under its own weight. If a “float” adorns the top of a cocktail, then a “sink”, well, sinks to the bottom, where it can add a surprising explosion of flavor. Once you understand how the specific gravity of liquids works and you develop the technique, you can layer the beverages until you feel like it.
However, some bartenders take a reverse approach: “letting most of a drink float” instead of “submerging a single ingredient”. Christmas is a time for overindulging, so Christmas cocktails tend to be rich in every sense of the word. Like the milk in the lattes at a local coffee shop, real cream is almost always guaranteed to float. Usually, a light beer is poured first and then a darker one (such as Guinness Stout) is placed on top.
While waiters tend to prefer this technique in whipped beverages, where aeration offers a slight advantage by allowing the mixture to float above the submerged ingredient, it can also work with whipped beverages. This effect is achieved by carefully pouring each ingredient into the glass so that it floats on top of its predecessor. In this classic cocktail, the blackest coffee you can create is sweetened with brown sugar and seasoned with Irish whiskey. Although most people mix the cream directly into the drink, you can turn the ordinary into an extraordinary drink if you float it instead.
A fun and extremely simple cocktail, the Harvey Wallbanger is little more than a screwdriver adorned with a liquor carriage.