What is the main ingredient in an Espresso?

The main ingredient in an espresso is indeed espresso itself. Espresso is a concentrated coffee beverage brewed by forcing hot water under pressure through finely-ground coffee beans. This process results in a strong, rich coffee that serves as the base for many other drinks, such as lattes or cappuccinos. The intensity and flavor of espresso are what set it apart from regular brewed coffee, providing a base that is essential to numerous coffee recipes.

Steamed milk, whipped cream, and mocha sauce are components that can enhance or complement various coffee drinks but do not constitute the fundamental ingredient of an espresso. In essence, espresso is the foundational element from which a multitude of espresso-based beverages are developed.