There are three layers to a shot of espresso, each with its own unique flavour and texture. The bottom layer is called the "crema", which is a rich and creamy foam that forms on top of the espresso. The middle layer is called the "body", which is where the majority of the coffee's flavour comes from. The top layer is called the "head", which is a thin layer of frothy foam that helps to protect the espresso from oxygen and keeps it fresh.