What aspect of espresso making cannot be controlled by the Mastrena® machine?

The Mastrena® machine is designed to facilitate the espresso-making process with precision and efficiency, but certain factors remain outside its control. The grind of the coffee beans is one of those elements. While the machine can automate many aspects of brewing, it relies on the grind size set in advance. The grind directly impacts the extraction process and overall flavor profile of the espresso being brewed.

Baristas must select the appropriate grind size to ensure optimal extraction. If the grind is too coarse, the water will flow through too quickly, resulting in under-extraction and a weak flavor. Conversely, if the grind is too fine, it may lead to over-extraction, causing a bitter taste. Since the grind must be adjusted manually prior to using the machine, it cannot be controlled by the Mastrena® once the brewing process begins, making it a critical variable that relies on the barista's expertise and choice.

Water, coffee, and time can all be adjusted or monitored by the machine, allowing for a more controlled brewing environment. However, the grind remains a manually set parameter, emphasizing the necessity for barista skill and knowledge in achieving the desired espresso quality.