Low static water debit and flow control

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#1: Post by jb-0101 »

Not the best title for my question, but it'll do...

I'm going to get a flow control device for my E61 DB, but until then I want to set my water debit to be optimal for light roast coffee ie Sey). Matt Pergers stuff said optimal is ~200ml/30 seconds (6-7ml/second) yet many of the standard and "optimal" flow profiles, ie Scott Raos, have that water debit only for a couple of seconds at the start to get the puck saturated, then drop significantly to 2-3ml/second.

Matt pergers stuff recommended against anything lower than 6ml/second as "If it's too low, you'll have a problem with low pressure in the puck. You'll have to grind so coarse that pressure cannot build up." And he also referred to another expert Matt Cameron who said "a lower water debit will result in a longer shot time. And you'd probably grind coarser to compensate." and "I'm all about bell curves at the moment, so I'd say that 200/280ml / 30 sec is somewhere at the top of an optimum water debit curve. 80/100ml I think would be on the wrong side of that peak" https://community.baristahustle.com/t/o ... ebit/782/2

Is this purely about achieving a standard brew time? And if you're ok with brew time being longer then low water debit is fine? What is the effect of longer shot time all other things being equal?

I guess it seems odd that he says 6-7ml/sec when many of the current flow profiles opt for much lower, despite an initial couple of seconds at 6-7. Has the consensus moved on since Matt recommend this or does flow control change the game?

If I had my water debit at 4ml/sec static, what negatives and positive results would I experience?

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#2: Post by Jeff »

First, a fact. If your flow is set by a valve or orifice of some type (such as a gicleur), the flow is related to the pressure across it. You can set "zero-pressure" flow. It won't stay at that level as the pressure rises in the basket.

Now, opinion. Anyone that tells you that they know the "optimal" basket-fill flow for one machine, coffee, grind, basket, water, extraction profile has perhaps confirmed that experimentally. Anyone that tells you that number applies everywhere is not someone I'd blindly take advice from.

(Note that, for example, lever machines can dump the 30 g or so of water needed to saturate the puck nearly instantly.)

If you're finding your puck does not extract uniformly at 4 mL/s static, see if increasing that significantly helps.

As 3-5 g/s or higher is now a "normal" extraction rate in some circles, your 4 g/s at 9 bar limiter might make reaching your desired pressure and flow challenging to impossible (without opening the valve).

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#3: Post by PIXIllate »

On my e61 (OPV set to ~8bar) I use 4 seconds at a flow control position of ~7.5ml/sec and then move to a ~4ml/sec position and then watch for the pressure to hit about ~3-4bar. At that point the puck is saturated, the bottomless is filled in and I'll start to watch the weight of the drops in the cup.

I then close the valve and maintain a ~2bar pressure until I hit 20-25 seconds total time since pump on with 1-2g in the cup (depending on the coffee) and then open back up to the 7.5ml/sec position.

At this point in the extraction I'm no longer thinking in terms of flow rate as the system is fully pressurized and now I'm watching just the grouphead pressure gauge as I close down the valve and watch the pressure drop down to ~6bar. At this point I stop adjusting and just let the shot finish until I hit my weight.

To Jeff's point my normal flow numbers are between 1.0 - 1.5ml/sec average with peak flow rates from 2-3.5ml/sec.

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#4: Post by matkuf22 »

What is the difference between flow rate and water debit? Is it the same thing? *hmmm...*

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#5: Post by Jeff »

"Water debit" and "flow rate" seem to be used interchangeably.

Don't assume that you know that the flow rate during extraction because of where the valve is set. It will be somewhat to significantly lower than that without a basket in place. Hence PIXillate's wording "at a flow control position of ..."