Many a cocktail calls for a twist, even dating back to Jerry Thomas’s time and of course Thomas was extra particular realizing that the twist is far more than just a decoration. A twist, much like bitters does actually influence the taste and complexity of the drink. As in cooking, the zest of citrus fruit adds a powerful punch of flavor because of the release of the essential oils. These essential oils have a flash point and the process of flaming twists has become a popular trick with many modern mixologists (see the MiddleBar Manhattan) and certainly adds to the flare of bartending.
Different methods can be used for cutting a twist by using a common bar knife to purchasing a citrus zester. (At MiddleBar we actually use a hand held cheese slicer knife).
When applying a twist to any cocktail, rim the glass entirely then “twist” it over the drink to release those important essential oils directly into it. Different schools of thought either toss the twist out or into the drink. I prefer to usually toss it in but even Thomas goes both ways in his recipes so the choice is yours.