Fines Migration
Fines Migration refers to the movement of extremely fine coffee particles toward the bottom of the coffee bed during espresso extraction. These fine particles accumulate at the filter basket and form a dense layer, which restricts water flow and slows down extraction in the initial phase. Research suggests that this migration primarily occurs when water is pumped through the coffee puck and is less influenced by the preparation process, such as grinding and tamping.
This phenomenon can lead to uneven extraction, where some coffee grounds are over-extracted while others remain under-extracted. As a result, the espresso may develop an unbalanced flavor profile, with excessive bitterness or sourness, reduced sweetness, and diminished aroma—ultimately compromising the clarity and complexity of the coffee’s flavor.