Turbulence is the physical disturbance of the coffee bed during brewing — from pouring, stirring or swirling.
What it does
Refreshes the water in contact with each particle. Coffee dissolving into stationary water reaches local saturation and slows; moving water keeps the gradient steep.
Evens the bed. Turbulence redistributes grounds, so channels and dry patches are disturbed.
Both raise extraction.
Where it is useful
A high pour from a gooseneck creates turbulence. That is why competition pours often start high.
A stir after the bloom wets everything and prevents dry pockets.
The Rao spin at the end flattens the bed evenly.
Where it goes wrong
Too much turbulence drives fines downward. They migrate to the bottom of the bed and clog the paper, and the draw-down stalls.
A brew that starts fast and then crawls is showing exactly this.
It also erodes the bed unevenly if the pour is aggressive and off-centre, creating a crater on one side.
The balance
Enough agitation to wet everything evenly. Not so much that the bed collapses.
For most pour-overs: bloom, stir gently, pour in controlled circles at moderate height, swirl once at the end.
Espresso
There is no useful turbulence during a shot — the bed is compressed. Agitation happens before, on the dry grounds, and it is called WDT.
Last reviewed 8 August 2026