What adjustment should be made if espresso shots are running shorter than 15 seconds?

When espresso shots are running shorter than the ideal extraction time of 15 seconds, the issue typically lies in the resistance to water flow through the coffee grounds. By making the grind more fine, you increase the surface area of the coffee beans. This allows for better water saturation and results in a longer extraction time, as the finer grind can slow the flow of water through the espresso basket.

A finer grind creates more resistance, which helps to achieve the desired extraction time, allowing flavors and oils to be properly extracted from the coffee. This adjustment is crucial for achieving the rich flavor profile that is characteristic of properly brewed espresso.

In contrast, making the grind coarser would reduce resistance and likely result in even shorter extraction times. Increasing heat or pressure could potentially complicate the brewing process and might not effectively resolve the issue with short shots. Therefore, fine-tuning the grind size is the most effective solution to achieve the ideal espresso extraction duration.