Fines Migration
Fines Migration refers to the phenomenon where fine coffee particles settle at the bottom of the coffee bed during shot (espresso) extraction, forming a dense layer on the filter screen. This can obstruct water flow, leading to uneven extraction and negatively affecting the overall flavor of specialty coffee.
If the extraction process takes too long, the coffee may become over-extracted, dissolving excessive bitter and astringent compounds, resulting in an unbalanced taste. To minimize fines migration, baristas can place a paper filter under the coffee puck to prevent fines from accumulating at the bottom, pre-wet the coffee bed before extraction to allow larger grounds to expand, reducing gaps between particles and slowing the movement of fines.
