Why is it advised not to stir after adding the espresso?

The advice against stirring after adding the espresso is centered on the concept of maintaining the distinct layers in the drink. When espresso is poured into a beverage, it often creates a visually appealing layer above other ingredients, such as milk or cream. This layering not only enhances the presentation but can also affect the flavor experience, as different parts of the drink can have varying intensities of taste. If the drink is stirred, these layers would mix together, resulting in a uniform mixture that loses the intended visual appeal and potentially alters the intended flavor profile.

Maintaining these layers allows the drinker to enjoy the espresso's robust flavor along with the creaminess of the milk, each sip providing a different taste experience. Thus, preventing the separation of layers is crucial for both aesthetic and taste purposes.