Flow rate is the volume of water passing through the coffee per unit time — millilitres per second in espresso, or the draw-down rate in a pour-over.
Why it matters
Flow rate is contact time expressed differently. Fast flow means short contact means less extraction.
It is also the most direct evidence of what the bed is doing, which is why scales that display flow rate exist.
In espresso
A 1:2 shot in 28 seconds is roughly 1.3 ml per second.
Much faster — grind too coarse, or channelling. Much slower — grind too fine, or the basket is blocked.
Rising sharply mid-shot is the signature of a channel opening. A flow-rate display shows this clearly where a stopwatch does not.
In pour-over
The draw-down rate tells you about fines migration. A brew that starts freely and then stalls means fines have moved down and clogged the paper.
The fix is a coarser grind or less agitation, not more patience.
Flow control
Some machines let you vary flow during the shot — a paddle, a needle valve, or a lever. Lowering flow at the start acts as pre-infusion; lowering it at the end can extend extraction without bitterness.
Genuinely useful, and well beyond what most people need.
The honest summary
Flow rate is a readout, not a control. You set grind, dose and distribution; flow is what results.
Use it to diagnose, and change the grind.
Last reviewed 8 August 2026