Firstly flow rate isn't a thing. Flow rate is a byproduct of time vs output. Even if you tie that to ratio (rather than an open ended output), time doesn't do enough of the work to get the job done, compared to grind size.

You grind coarser to pull shots at a longer ratio & finer to pull shots at a shorter ratio.

If you ground fine & pulled a high flow shot, it would likely be silty.

 

Apologies, should have specified input flow rate at the group by varying via a flow control valve (a la Lelit/ECM kit).

Surely more water through a puck of a given grind size and during a given amount of time would lead to greater extraction, the same way a finer grind facilitates higher extractions (before cut-off)? Or have I got it totally wrong?

 

Apologies, should have specified input flow rate at the group by varying via a flow control valve (a la Lelit/ECM kit).

Surely more water through a puck of a given grind size and during a given amount of time would lead to greater extraction, the same way a finer grind facilitates higher extractions (before cut-off)? Or have I got it totally wrong?

More water through a puck of given grind size will extract more, in the same, or less time.

Even fine grinds are rarely producing high extractions (compared to coffee brewing generally, or over-extraction for espresso specifically).

If you're asking can you raise extraction by slowing flow at the same grind size & ratio, then possibly, a little. Enough is enough.

If you are asking can I salvage 'way out of the ball-park grinds', by playing with flow...probably not. You may as well push more water through the puck, get a weak but tasty shot & adjust finer for next one.

 

You can salvage way of grinds by playing with flow rate but you do have to alter the ratio. A very low flow rate with a very fine grind can also be called a choker; it's determined by grind size assuming you've capped pressure (which everybody has). You can't increase flow rate through a very fine grind assuming you're at full pressure.

With a coarse grind you can alter flow rate, say to stop a gusher, but it wouldn't be similar to a shot with a finer grind that creates more resistance. Higher flow rates are probably better with higher ratios rather than restricting flow with a valve.

 

All makes sense. Not trying to salvage some extreme grind, purely interested in whether small shifts one way or another can be compensated for by flow rate.