Matt Perger on Water Debit / Flow Rate

#1: Post by **NoStream** » September 22nd, 2015, 2:58 pm

Matt Perger wrote:Pump Pressure: Pressure and flow rate are kind of the same thing in espresso. Because the coffee doesn't form a complete blockage, it's safe to say it doesn't really experience 9 bars of pressure (especially not the lowest grinds). If you can't change the restrictors, reducing pump pressure is your next best bet. Have a play with your espresso machine's pump, aiming to hit the 150-250ml/30sec mark. Go all the way down to 4 bars if necessary. Don't fret; 4 bars is still a lot of pressure, and you'll still get your precious cremaz.

https://coffeehustle.com/posts/pEcQmYA3 ... an-apology

I'm curious what you all think of MP's recent thoughts on the flow rate of espresso machines. The traditional method would be to tweak the gicleur, but he's also suggesting pump pressure as an option - all the way down to four bars if necessary! (I did a bit of Googling and noticed another_jim using the term "water debit" for this concept, though he used the first 10s rather than 30s.)

What volume per 10s or 30s do you think is ideal? Is adjusting pump pressure a valid way to tweak water debit?

Just speculating here... too low of flow rate would probably mean over-long pseudo pre-infusion, over-coarse grind (less extraction). Over-high flow rate, which I think is likely more common and more problematic, would mean aggressive pressure ramping and more risk of channeling and uneven extraction.

In my vibe pump CC1, I'm getting ~290 ml in 30s from ~8 bars at the grouphead. I've noticed reduced EYs from pressures below ~6 bars but have not measured flow rate at that pressure. I'm not entirely clear how adjusting an OPV would also adjust flow-rate, though...

#2: Post by **boost** » September 22nd, 2015, 3:21 pm

Note that he says to change pump pressure if you can't change the flow restrictor. 4 bars is really low and I would be really surprised that if he goes anywhere that low in his shop. I think this is really misleading.
The purpose of flow restrictor is to slow down the initial flow rate. Only when the puck is fully saturated then it is in fact becomes a restrictor itself. This is why you have flow rate around 30-40 g per 30 second when you are actually pulling a shot. Compare this to 250mL if you just run it through your 0.7mm gicleur. Anybody that has Strada gauge on MP La Marzococo knows that when you are pulling a shot the pressure gauge shows close to 9 bar. This is post gicleur pressure and really shows the pressure on the top of the puck.
But hey what do I know, I'm just home barista not WBC barista.

#3: Post by **brianl** » September 22nd, 2015, 4:40 pm

Wasn't he specifically talking about the EK43? In that you might not be able to grind fine enough with certain coffees so then you would need to reduce flow?

September 22nd, 2015, 5:25 pm

He's I think you're right that he's mostly referring to the EK, but I'm curious what people think with regards to both the EK specifically and grinders in general.

September 22nd, 2015, 7:38 pm

I bet the EK is similar to the R120 in that they are all purpose grinders. When I got the R120s they both weren't tight enough to do espresso even dialed all the way down. Which is WEIRD as the way to set the burrs is just like any other grinder, tighten until they touch, back off a tick and call that Turkish.

To get the R120 to do espresso for real in the 'espresso' range of the grinder dial means the rest of the dial isn't accurate IME.

I'm betting that's what he was talking about. Grind settings aren't as simple as the dial suggests on a Bunn G1!

#6: Post by **boost** » September 22nd, 2015, 7:56 pm

NoStream wrote:He's

I think you're right that he's mostly referring to the EK, but I'm curious what people think with regards to both the EK specifically and grinders in general.

Yeah thats the confusing part. If you can afford an EK then for sure you should have a flow restrictor in your machine. If you are running unrestricted machine, even non gicleured Linea I seriously doubt cutting the pressure in half would reduce the flow equal to gicleured one, its not quite a linear relationship.

#7: Post by **TomC** » September 22nd, 2015, 8:02 pm

Prescott CR wrote:I bet the EK is similar to the R120 in that they are all purpose grinders. When I got the R120s they both weren't tight enough to do espresso even dialed all the way down. Which is WEIRD as the way to set the burrs is just like any other grinder, tighten until they touch, back off a tick and call that Turkish.

To get the R120 to do espresso for real in the 'espresso' range of the grinder dial means the rest of the dial isn't accurate IME.

^ This.

I noted the same thing when I had the Ditting 1203 and now the R120. Whether its tooth geometry, their specific design being different than say the Major's burrs, something, they all need less flow thru the puck. I don't care to get pretty pours with the R120 as long as they're tasty. And I'd been at 8 bar with the conical (K10) since getting the Linea. Although, I can choke the Linea at 8 bar without even leaving the "espresso" setting on the R120, so I think it's more about finding that razors edge grind setting on these big flat burrs.

#8: Post by **Bunkmil** » September 22nd, 2015, 8:27 pm

NoStream wrote:In my vibe pump CC1, I'm getting ~290 ml in 30s from ~8 bars at the grouphead. I've noticed reduced EYs from pressures below ~6 bars but have not measured flow rate at that pressure. I'm not entirely clear how adjusting an OPV would also adjust flow-rate, though...

I'm not sure that we can apply this to vibe pumps. When I look at the flow rate graph of a vibe pump, I understand that lowering the pressure by adjusting the OPV actually increase the flow rate. Unless I'm missing something...

http://users.rcn.com/erics/ · #9: Post by **erics** » September 22nd, 2015, 9:39 pm

Should anyone be interested in the "history" of water debit, it is found in the Google Archives: https://groups.google.com/forum/#!topic ... nob3C5oBWQ . The initial post by Al Critzer (sp) to the alt.coffee newsgroup (April 2002) is posted here below:

(MIS)UNDERSTANDING WATER DEBIT

As has been explained to me, acceptable water debit through an empty portafilter should be between 65ml (2.15oz) and 90ml (3oz), accomplished in 10 seconds, with 90ml being optimum. This assuming that other variables are constant, i.e., pump pressure and temperature, regulated by the delivery system of a given machine.

Water debit at or below the optimum level would result in coarsening of the grind to achieve an appropriate contact time of water to ground
coffee, and the resulting coarseness and reduced surface area would lead to an under extracted cup. Too high a debit would encourage a
tightening of the grind to conform to the same contact time, usually resulting in over extraction.

A few facts:

Coffee offers minimal resistance to cold water under pressure. The colder, the less resistance, although I don't know what subfreezing
temperatures would do. Water that is approaching boiling or above will pass through coffee as quickly as cold water, with completely different results. In either case, optimal extraction of the positive solubles is not accomplished. 7 grams of coffee will absorb approximately 15ml of water during a proper extraction. This increases proportionately for 2 and 3cup applications. Water debit is not effectively measured in 1sec increments, as some posters imply. There is some time that should be allocated for the ramp-up time and time it takes to fill the empty portafilter. What
matters is what's in the cup. Water will flow differently from different machines, as temperature changes and flow rates vary when cold water displacement occurs during extraction.

Displacement temperature varies greatly between single boiler, heat exchangers and dedicated boiler machines. In short, water flow is a critical component in proper extraction, as important as temperature, pump pressure, portafilter configuration or any other factor, and outside of the cognizant faction of this newsgroup, often overlooked. Before you adjust your grinder, measure your water debit.

#10: Post by **Bunkmil** » September 23rd, 2015, 12:07 pm

So if we have a flowrate of 65ml-90ml/10sec with no portafilter there is no need to look at the pressure ?