# Water debit (Flow rate) on espresso machines



## MediumRoastSteam

I've recently been reading about flow rates and pressure, and how that can affect your shot quality.

So, the fact is, prosumer machines tend to be set so that the pump delivers 9bar at the group while brewing. Other machines like the Gaggia Classics and alike are set to 13-14bar from the factory as they are equipped with pressurised porta filters, and people tend to adjust the OPV later on.

So, from what I read, there is also the optimal flow rate. I checked on my machine and the flow rate seems not to be optional according to literature. The rule seems that the best bet other than installing a flow restrictor is to adjust the pump to reach a flow rate between 60ml and 90ml in 10 seconds, with 75ml optimal. (for reference, 1ml of water is 1g).

So, I did that test and my machine is not in that range. If possible, I would like to encourage forum members to share what their flow rate is to have an idea how machines are configured.

So, I start:

0. Machine | Pressure | FLow in 10s | Member

1. Profitec 700 | 9 bar | 110ml. | pessutojr


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## dlight

2. VBM Replica. |. 6 bar. |. 115ml. |. Dlight


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## Jason1wood

3. Verona | 9 bar | 105ml | jason1wood


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## DavecUK

I saw this and thought I had better try to prevent going down a rabbit hole with this one.



> I've recently been reading about flow rates and pressure, and how that can affect your shot quality. So, the fact is, prosumer machines tend to be set so that the pump delivers 9bar at the group while brewing. Other machines like the Gaggia Classics and alike are set to 13-14bar from the factory as they are equipped with pressurised porta filters, and people tend to adjust the OPV later on.


The Gaggias are not set to 13-14 bar at the factory, the cheap expansion valve they use comes from the manufacturer set to about 14/15 bar. It is vaguely adjustable, but only when diassembled and it's response is non linear. It can't be adjusted with the machine running.

Having a pressurised portafilter is just so they can make crema from anything, nothing to do with the expansion valve.



> So, from what I read, there is also the optimal flow rate. I checked on my machine and the flow rate seems not to be optional according to literature. The rule seems that the best bet other than installing a flow restrictor is to adjust the pump to reach a flow rate between 60ml and 90ml in 10 seconds, with 75ml optimal. (for reference, 1ml of water is 1g).


Did you read that for your specific machine, or was this for some generic machine, was it for a rotary pump or for a vibration pump, did it even mention the Gicleur size? The water debit of a Vibe pump machine will usually be a direct function of the Gicleur size e.g. for 0.7mm Gicleurs (if not scaled) the same vibe pump (or pumps with the same flow curve), will debit a very similar amount of water at 9 bar. Closing the expansion valve (thus raising the pressure) may increase this a little, but flow rate is inverse proportional to the pressure on a vibe.

Mmachines already have flow restrictors and pump pressure adjustment is via the expansion valve, the problem is the numbers your quoting don't really make sense.

e.g. Machine set to 6 bar with 0.7mm gicleur may debit a lot of water in 10s, another machine set to 9 bar with a 0.5mm gicleur may debit less, but these numbers are fairly unimportant. If you are pulling a double shot at 8-10 bar, your pump may have to debit 60 ml in 28 seconds. What it debits with a 0.5 or 0.7 gicleur at 9 bar is not very relevant. With a Vibe pump machine your going to adjust to 9 bar against a static load (minue any water expansion effects) for the convention that you then control grind to get the correct flow rate for that max pressure against a static load.



pessutojr said:


> So, I did that test and my machine is not in that range. If possible, I would like to encourage forum members to share what their flow rate is to have an idea how machines are configured.


If your machine is set to 9-10 bar and you have a Gicleur of 0.5 - 0.7mm in it (which you will), don't worry about your flow rate with an empty group. Just concentrate on your grind to get the right flow through coffee for the shot...thus ending up with the desired amount of espresso at the end of your desired extraction time.

In the other route...lies madness


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## MediumRoastSteam

DavecUK said:


> I saw this and thought I had better try to prevent going down a rabbit hole with this one.
> 
> The Gaggias are not set to 13-14 bar at the factory, the cheap expansion valve they use comes from the manufacturer set to about 14/15 bar. It is vaguely adjustable, but only when diassembled and it's response is non linear. It can't be adjusted with the machine running.
> 
> Having a pressurised portafilter is just so they can make crema from anything, nothing to do with the expansion valve.
> 
> Did you read that for your specific machine, or was this for some generic machine, was it for a rotary pump or for a vibration pump, did it even mention the Gicleur size? The water debit of a Vibe pump machine will usually be a direct function of the Gicleur size e.g. for 0.7mm Gicleurs (if not scaled) the same vibe pump (or pumps with the same flow curve), will debit a very similar amount of water at 9 bar. Closing the expansion valve (thus raising the pressure) may increase this a little, but flow rate is inverse proportional to the pressure on a vibe.
> 
> Mmachines already have flow restrictors and pump pressure adjustment is via the expansion valve, the problem is the numbers your quoting don't really make sense.
> 
> e.g. Machine set to 6 bar with 0.7mm gicleur may debit a lot of water in 10s, another machine set to 9 bar with a 0.5mm gicleur may debit less, but these numbers are fairly unimportant. If you are pulling a double shot at 8-10 bar, your pump may have to debit 60 ml in 28 seconds. What it debits with a 0.5 or 0.7 gicleur at 9 bar is not very relevant. With a Vibe pump machine your going to adjust to 9 bar against a static load (minue any water expansion effects) for the convention that you then control grind to get the correct flow rate for that max pressure against a static load.
> 
> If your machine is set to 9-10 bar and you have a Gicleur of 0.5 - 0.7mm in it (which you will), don't worry about your flow rate with an empty group. Just concentrate on your grind to get the right flow through coffee for the shot...thus ending up with the desired amount of espresso at the end of your desired extraction time.
> 
> In the other route...lies madness


Hi @DavecUK, thanks for the feedback as always. It is always great to hear from someone who actually has in depth knowledge of machines and how they work. I am just relatively new to all of this, so just trying to learn and understand.

What made me think about all of this? Basically reading about pump pressure and flow rates, I got here due to this statement from Mr. Perger:

"4. 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."

Source: http://www.baristahustle.com/nutation-an-apology/

And testing the flow rate on the machine I have, I noticed that I am way off the mark. From the two forum members who shared their water debit values, they are very close to what my machine is. So, my question is: What's Mr. Perger on about? Why is the flow rate he states in his post so different from at least the three machines aforementioned?


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## DavecUK

pessutojr said:


> So, my question is: What's Mr. Perger on about? Why is the flow rate he states in his post so different from at least the three machines aforementioned?


Who knows? Just because he is a world champion Barista doesn't necessarily imbue him with knowledge in all areas of coffee, machine, roasting, physics and chemistry. There is a difference between static and dynamic flow and the use of restrictors to control pressure on standard prosumer machines, rather than the expansion valve or rotary pump bypass valve is a new one on me. I suspect he was still at school when I did the Top level Duetto design, so he may lack the benefit of experience and his views might change over the next 5 or 10 years.....as they did with nutation!

As for who you want to believe..."you pays your money and you takes your choice", in my case the advice is free....so perhaps it's worth what you pay for it...nothing, but that's for you to decide.


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## MediumRoastSteam

DavecUK said:


> Who knows? Just because he is a world champion Barista doesn't necessarily imbue him with knowledge in all areas of coffee, machine, roasting, physics and chemistry. There is a difference between static and dynamic flow and the use of restrictors to control pressure on standard prosumer machines, rather than the expansion valve or rotary pump bypass valve is a new one on me. I suspect he was still at school when I did the Top level Duetto design, so he may lack the benefit of experience and his views might change over the next 5 or 10 years.....as they did with nutation!
> 
> As for who you want to believe..."you pays your money and you takes your choice", in my case the advice is free....so perhaps it's worth what you pay for it...nothing, but that's for you to decide.


Thanks. There has been other members in this forum who have experimented with lowering the pressure to 6bar, some even reporting better tasting shots. I was inclined to test it all, but part of me started thinking "why".

Once again, thank you for the explanation and clarification.


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## Mrboots2u

Try stuff - does it work for you or not .

Me I like lower pressure shots with, yes a reduced water debit too..You may not ....

Doesn't mean anyone is definitely " right " me - Dave or mr perger but it shouldn't stop people trying this stuff and deciding for themselves. @Xpenno


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## Nikko

Since Bernoulli published his Hydrodynamica in 1738, it has been known that for flow of incompressible fluids changes in kinetic energy manifest as changes in pressure and vice versa. From physics point of view Perger is spot on although on most machines it is probably easier to change the pump pressure than the restrictor. No matter how done, the end result will be the same.

Also there is no practical difference in the output of rotary and vibratory pumps - one limits its output pressure with an internal by-pass, the other with an external diverter.

The different pressures and flows reported for the various machines simply means that they have been adjusted differently and/or have different characteristics and consequently will produce different tasting coffee if presented with identically prepared portafilters.

No harm in experimenting.


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## GlennV

pessutojr said:


> And testing the flow rate on the machine I have, I noticed that I am way off the mark. From the two forum members who shared their water debit values, they are very close to what my machine is. So, my question is: What's Mr. Perger on about? Why is the flow rate he states in his post so different from at least the three machines aforementioned?


Assuming a rotary pump set to 9 bar, and a single flow restriction, you need a 0.5mm gicleur to get down to around 60ml/10sec. 0.6 would give around 85-90, 0.7 around 115 and 0.8mm around 150ml/10sec. The flow rate varies with the area, ie with the square of the diameter, hence why it changes so rapidly. However, it changes only as the square root of pressure, and so you have to make large changes in pressure to make a noticeable difference. It sounds like you have a 0.7, which is not uncommon. The quickmill machines have an extra restriction at the pump, which is why they flow slightly less with the same gicleur in the group. None of this is new, there's a nice discussion on the alt.coffee archives from 2002 (go up and click on the first post from ...al, Al Critzer).

https://groups.google.com/forum/#!topic/alt.coffee/enob3C5oBWQ

If anyone's interested, the formula for flow rate in ml/10 sec is, approximately, sqrt(2*P*100)*pi*(D)^2/4*10*0.7. Replace P with the actual pressure in bar, and D with the actual gicleur diameter in mm. The 0.7 is a fudge factor (properly called the "discharge coefficient" and depends on all sorts of details, and is chosen here to match observed numbers in espresso machines.


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## Dylan

That last paragraph of your post mangled my brain.


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## GlennV

Sorry. how about 78*sqrt(P)*D^2 ?

It's the way it varies with pump pressure P and gicleur size D that I was trying to convey.


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## Dylan

It says squirt in the middle.


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## DavecUK

Nikko said:


> Since Bernoulli published his Hydrodynamica in 1738, it has been known that for flow of incompressible fluids changes in kinetic energy manifest as changes in pressure and vice versa. From physics point of view Perger is spot on although on most machines it is probably easier to change the pump pressure than the restrictor. No matter how done, the end result will be the same.
> 
> Also there is no practical difference in the output of rotary and vibratory pumps - one limits its output pressure with an internal by-pass, the other with an external diverter.
> 
> The different pressures and flows reported for the various machines simply means that they have been adjusted differently and/or have different characteristics and consequently will produce different tasting coffee if presented with identically prepared portafilters.
> 
> No harm in experimenting.


Te statement about Rotary and Vibe pumps is correct, *apart from the flow rate capability of each* which is different. Part of the comment about different pressures giving potentially different tastes to shots is true.

The rest of it, no, because you are forgetting the very big restrictor at the end of the brew path called a coffee puck. If any given machine set to the same pressure gives the same rate of pressure rise, when extracting the same coffee ground to the same fineness as an espresso over say the same 27s, the flow rate is the same for the same volume extracted.

It doesn't, within reason, matter what the free flow rate of the machine is without coffee. It's rather like having a 300 mm water pipe draining a swimming pool and, placing a 100mm pipe on the end of it. You will get a lower flow rate replace with a 200mm pipe instead of a 100mm pipe you get a different flow rate. *If then on the end of each of those 100 or 200 mm pipes, you place a 10mm restrictor and repeat the test* you will get the same flow rate in each case (well not absolutely, but almost).

Ultimately what controls flow rate is the coffee puck....the max static pressure (you set a machine to) is the largest "push" that can be applied to the puck. The max pressure will in practical terms. be achieved when the flow rate of the puck is less that the capability of machine to deliver water. The fact that most machines have a small enough Gicleur to bring them fairly near to this point (especially rotary pumped machines) when pressure is measured between the pump and the Gicleur, means that for all practical terms that point is usually reached without any help from the coffee puck.

The evidence for all this exists all around you in multi group (non lever) machines in coffee shops. They all have pumps capable of treble or quadruple the flow rate of the small pumps in prosumer machines. I have yet to hear anyone postulate that there is a different taste when pulling a shot from a single group or 3 groups at once and clearly the flow rate would be different for each scenario and no one goes changing the gicleurs/restrictors on the groups in this scenario.

I once had a espresso designer tell me I was wrong about the length of time a 2 litre steam boiler would take to heat, I said I wasn't, so he bombarded me with equations, all of which were correct....his case made they were going to design the machine around his theory. Until I mentioned that with all the math, he had forgotten one thing. The 2 litre steam boiler was only ever going to be about 60-70% full, not 100% full.. It's rather like forgetting the big coffee puck on the end of the brew path. Or for that matter people who complain about a small nick on the burr of a grinder (well away from the outer rim). They worry like hell about it, 100s of people will tell them about the effect on grind quality, they will even report how they feel the grind quality has changed....somehow though the big screw holes securing the burrs (on smaller grinders), never bother them in the slightest?

*We can convince ourselves of a lot of things based on all sorts of data (whether correct or not). For standard non profiling machines the most important things are the quality of the roasting/roasted coffee, temperature, max pressure your pump is set to, grinder and grind quality. Get these right and you won't go far wrong....*


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## Nikko

Hello Davec

I think we can agree that the resistance of the coffee puck is by far the dominant factor in determining the final flow.

What controls the flow through the coffee is the pressure drop across the whole path, i.e. from the outlet of the pump to the outside of the basket. If you put a restrictor in the path, then the flow will change depending on the properties of the restrictor because the pump outlet is fixed (by the internal by-pass or OPV) and the pressure at the bottom of the basket is atmospheric. The pump delivery capability has typically nothing to do with it because it exceeds by far what is needed, hence the internal by-pass or OPV).

I am afraid your bringing into the discussion irrelevant aspects may have confused some. You say:

"I have yet to hear anyone postulate that there is a different taste when pulling a shot from a single group or 3 groups at once and clearly the flow rate would be different for each scenario and no one goes changing the gicleurs/restrictors on the groups in this scenario."

Why would anybody say that as they all behave identically since they all see the same outlet pressure.

The discussion was about the effect on taste by reducing the flow. How that flow reduction is achieved is neither here nor there as far as the coffee is concerned.

At the end you said:

*
"For standard non profiling machines the most important things are the quality of the roasting/roasted coffee, temperature, max pressure your pump is set to, grinder and grind quality. Get these right and you won't go far wrong...."*

Spot on. Why contradict it with your previous comments?


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## Nikko

May I make a plea for the use of english words when good alternatives exist. As one who has worked on carburetors in the past, I can well imagine what my mates would have called me if I had used the words gicleur or debit instead of their more common english equivalents.


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## GlennV

Dylan said:


> It says squirt in the middle.


How about 80 times D squared times the square root of P ?


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## MediumRoastSteam

Thanks for all the technical input. Now, the questions that I am interesting in finding the answer for, based on the explanation above are:

1) Where does the 9bar pressure for espresso extraction comes from?

2) If a lower flow rate is beneficial (60-90ml) - as mentioned by some - why espresso machine manufacturers design machines with a higher flow rate (105-115ml) based on the brief sample in the first posts)? If it makes such a great difference, why don't manufacturers just restrict the flow rate?

We could limit the scope discussion by restricting to non pressure profile machines equipped with rotary pumps.


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## DavecUK

pessutojr said:


> Thanks for all the technical input. Now, the questions that I am interesting in finding the answer for, based on the explanation above are:
> 
> 1) Where does the 9bar pressure for espresso extraction comes from?
> 
> We could limit the scope discussion by restricting to non pressure profile machines equipped with rotary pumps.


The 9 bar, comes from a long time ago, I think when the E61 was invented they came up with the 9 bar (or was it Illy)....was it because typically that's what the lever machines of the time could easily produce, was it guesswork...I have no idea. Is 9 bar the correct pressure for extraction), again I don't know. I have personally not found much difference in pressures between 8.5 to 10.5 bar...but that's just my experience and all comments within the specific scope of discussion you set.

I suspect it's like asking why is the max temperature on a Gicar PID controller hard coded to the value it is for prosumer steam boilers .... for the PID it was a best guess at a good value, that's all.


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## GlennV

pessutojr said:


> Thanks for all the technical input. Now, the questions that I am interesting in finding the answer for, based on the explanation above are:
> 
> 1) Where does the 9bar pressure for espresso extraction comes from?
> 
> 2) If a lower flow rate is beneficial (60-90ml) - as mentioned by some - why espresso machine manufacturers design machines with a higher flow rate (105-115ml) based on the brief sample in the first posts)? If it makes such a great difference, why don't manufacturers just restrict the flow rate?
> 
> We could limit the scope discussion by restricting to non pressure profile machines equipped with rotary pumps.


1) According to Illy, it maximises the flow rate through the puck.

2) Because not everyone agrees? A bunch of us bought and fitted 0.5mm group jets/gicleurs/gigglers a while back, and there's no doubt you have to grind finer to get the same shot times because of the way it slows down the initial wetting of the puck (ie before the puck takes over as the thing responsible for restricting flow). This is a bonus for lighter roasts, but can make it difficult to avoid over extracting darker roasts.


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## MediumRoastSteam

@DavecUK, @GennV, thank you!


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## Nikko

pessutojr said:


> Thanks for all the technical input. Now, the questions that I am interesting in finding the answer for, based on the explanation above are:
> 
> 1) Where does the 9bar pressure for espresso extraction comes from?
> 
> 2) If a lower flow rate is beneficial (60-90ml) - as mentioned by some - why espresso machine manufacturers design machines with a higher flow rate (105-115ml) based on the brief sample in the first posts)? If it makes such a great difference, why don't manufacturers just restrict the flow rate?
> 
> We could limit the scope discussion by restricting to non pressure profile machines equipped with rotary pumps.


To take your second question - Like everything else, coffee machines are manufactured to a tolerance and price. Also, the internals of coffee machines vary so with the standard 9 barg their flows will also vary.

You have the means to adjust your machine to what suits you. I suggest you drop the pressure to 6 barg to see if you like the result


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## MediumRoastSteam

Thanks Nikko


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## Nikko

DavecUK said:


> The 9 bar, comes from a long time ago, I think when the E61 was invented they came up with the 9 bar (or was it Illy)....was it because typically that's what the lever machines of the time could easily produce, was it guesswork...I have no idea. Is 9 bar the correct pressure for extraction), again I don't know. I have personally not found much difference in pressures between 8.5 to 10.5 bar...but that's just my experience and all comments within the specific scope of discussion you set.
> 
> I suspect it's like asking why is the max temperature on a Gicar PID controller hard coded to the value it is for prosumer steam boilers .... for the PID it was a best guess at a good value, that's all.


Again you are throwing in unrelated things that confuse.

I imagine that Gicar have coded in a max temperature for the steam boiler for safety reasons - no reasons for guesswork

The 9 barg limit on pump output is not safety related but coffee making related. For better or worse it is the accepted norm.


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## DavecUK

Nikko said:


> Again you are throwing in unrelated things that confuse.
> 
> I imagine that Gicar have coded in a max temperature for the steam boiler for safety reasons - no reasons for guesswork


Only to provide an example of how some things in coffee have developed out of guesswork...perhaps more than we think. I assure you the max temp coded by Gicar was not for safety reasons, it was based on a best guess of what would feel like a good value.


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## dlight

Wow, what an interesting burst of comments. For what it's worth, I've just moved to 6 bar and I'm very happy with it. I've commented in another post about this.


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## bronc

To put things in a simpler perspective - does changing vibe pumps' pressure via the OPV have the same effect as changing it on a rotary? Would it make any sense to set my vibe pump machine to 6bar (7bar static) or should I play with the gicleur size?


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## DavecUK

bronc said:


> To put things in a simpler perspective - does changing vibe pumps' pressure via the OPV have the same effect as changing it on a rotary? Would it make any sense to set my vibe pump machine to 6bar (7bar static) or should I play with the gicleur size?


It has the same effect, but I think you might find the pressure you want to set a bit low. I'm not really sure exactly what you mean by 6 bar (7 bar static)?


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## MediumRoastSteam

DavecUK said:


> It has the same effect, but I think you might find the pressure you want to set a bit low. I'm not really sure exactly what you mean by 6 bar (7 bar static)?


I think the 6 bar figure comes from a couple of posts above.

6 bar (7 bar static) I believes comes from the belief that, 7 bar measured with a pressure gauge at the group with no water going through equates to 6 bar in normal conditions with a basket of coffee loaded instead. (That's what I used to read on the Internet by trying to adjust the Gaggia Classic pressure, as information would state that one should adjust the OPV to 10 bar showing on the home-made pressure gauge in the group) and that would mean roughly 9bar in normal brewing conditions.

As per this post on this forum, back in 2011:

"8. This is known as a static pressure test which means there's no flow through the portafilter. The pressure you should be aiming for is 10 bar not 9 bar. This is because the difference between a static reading of 9 bar and a dynamic reading i.e. with flow through the head is 1 bar less. Therefore you need to set your machines to 10 bar which will give you 9 bar dynamic."

http://coffeeforums.co.uk/showthread.php?3859-Adjusting-the-OPV-(over-Pressure-Valve)-Gaggia-Classic


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## DavecUK

I dunno, I think 9 bar static is better...but up to you.


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## bronc

I want to try 6 bars as per MPs suggestions. Maybe it's an EK thing, maybe it's nonsense but as with most coffee things experimentation is the way to go


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## Mrboots2u

bronc said:


> I want to try 6 bars as per MPs suggestions. Maybe it's an EK thing, maybe it's nonsense but as with most coffee things experimentation is the way to go


Discussion of setting the optimal pressure of extraction have been in Scott Roa s books before this .

I wouldn't say it's per se an Ek thing . Most of the newer posts on it are concerning using a Myhtos ...


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## Jumbo Ratty

pessutojr said:


> 0. Machine | Pressure | FLow in 10s | Member
> 
> 1. Profitec 700 | 9 bar | 110ml. | pessutojr





dlight said:


> 2. VBM Replica. |. 6 bar. |. 115ml. |. Dlight





Jason1wood said:


> 3. Verona | 9 bar | 105ml | jason1wood


Gaggia Classic RI8161/40 / factory set (14bar) / 100mls / Jumbo Ratty.

OK,,, I timed some running times. These are all timed from when the switch was switched on to off and without the portafilter in place and when the light indicated it had reached the required temperature.

I found a few variations though, the first timed run was 100mls in 15 seconds. This was the first timed run from the machine being turned on and ready to roll and took a few seconds for the water to appear after flicking the switch

I did a second timed run of 200mls to check the time and it was in 20 seconds, the water appeared immediately this time.

I waited a while and did a third, again the water was immediate and 200mls took 20 seconds.

After now timing about 5 separate 200mls im happy to report 20 to 21 seconds being the time taken, I opted for 200mls as it was easier to see the level in my jug.


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## Mrboots2u

Weigh the water perhaps ???


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## Jumbo Ratty

Mrboots2u said:


> Weigh the water perhaps ???


Yes boss.

199.3gms is what my 200mls weighs


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## matisse

Jumbo Ratty said:


> Yes boss.
> 
> 199.3gms is what my 200mls weighs


that'll be the temp. water is less dense at the higher temp and so will weigh less on the scales. but, tbh its still close enough to 1g-1ml


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## Jumbo Ratty

got to be honest, but some difference in mls to gms could be down to how "on the line" the water is in the jug.







A blind basket full of water didnt make much visual difference.

At eye level this was bang on the line


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## Scotford

Gonna wade in here with my experiences down low.

A couple of weeks ago, I decided to take the plunge and go low pressure, mainly to see what I could come up with without affecting service standards.

18g dose, 36g yield, 29-31 second extraction time for one week as a constant. 10-14 days post roast.

8bar - no noticeable difference to usual, same taste notes across all staff. EY avg 21.2%

7.5bar - As above, less channeling than usual across all staff. EY avg 20.8%

7bar - Sweeter in all tastings, noticeably more well balanced. Very few channeled shots the entire day. EY avg 21.1%

6.5bar - Zero channeled shots across the board, I spent the entire day pulling shots and shot times were bang-on and yields were more accurate than usual (to within .5g target 9/10 times). Insanely well balanced espresso with just the right amount of sweetness and such a delicious mouthfeel, acidity and fruitiness. EY avg 21.7%

6bar - EY up again!!! 22.0% avg. Tastiest shots of the lot. The body was silkier than ever, the sweetness was more pronounced than ever, the acidity was so moreish, the apricots were swimming in brandy IN OUR MOUTHS. Best shots by far.

5.5bar - EY avg was the same. Shots starting to become slightly unbalanced.

5bar - Not great if I'm honest. lasted an hour down here until I went straight to 6 and that is where we have stayed since.


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## DavecUK

Scotford said:


> Gonna wade in here with my experiences down low.
> 
> 5bar - Not great if I'm honest. lasted an hour down here until I went straight to 6 and that is where we have stayed since.


Sounds like I need to do some taste testing with the Vesuvius.

edit: Thought I should add a little warning. When testing many machines, especially those with less than excellent expansion valves, they often won't work reliably down at 6 bar and/or will leak (into the machine from the adjuster) during the shot! So people trying this out should do it carefully and check that their expansion valve isn't leaking during the shot.


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## MediumRoastSteam

Scotford said:


> Gonna wade in here with my experiences down low. ...


What machine do you have?


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## Scotford

pessutojr said:


> What machine do you have?


Linea PB


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## christos_geo

Seeing as this has slightly moved to a 6 bar vs 9 bar conundrum, I recommend reading this very relevant article on the matter by Michael Cameron. Comes to same conclusions as @Scotford with a ton of statistics thrown in showing increased EY amongst other things. (https://strivefortone.com/2016/05/18/this-low-pressure-rehash/)

I am going down to 6 bar for the week to see how it pans out.

Keep up the good posts


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## Scotford

It was interesting to see that EY went up consistently all the way until a peak at around 5.5-6bar. I'd like to see some more data on why or do another week of testing to come to my own conclusions but I'm not sure when I'll get a chance.

Things to note: the trial I wrote about was using a Linea PB with a Mythos 1 and an Atago refraccer. I'd (painstakingly) aligned the M1 burrs the day previously too.

Water debit is 205g per 30sec at 9bar (all three groups hit within 2g yay!) on a stripped group head with .7mm flow restrictor fitted.

The PB had been calibrated a week earlier with a Scace across the pressure spectrum. It actually came so close on the dial that there was minimal margin of error.

I did try this with the same blend, dose, yield, shot times, water specs and refractometer a week later but with a Mazzer Major and Linea Classic with a water debit of 230g per 30sec at 9bar. EY was unaffected across the board (19.8% avg with a slight increase of .1% consistently at 7bar before settling back into 19.8% at 6.5) and taste improved but on a more marginal level. I got less body and finish from most shots I tried down low which puzzled me and acidity was more pronounced at around 7bar before becoming almost unpleasant lower.

Whilst I did come to the same conclusions as Michael Cameron on very similar equipment, i'm not going to tell anyone to expect the same results on different kit.


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## MediumRoastSteam

Very interesting. I lowered the pressure on my machine today to 6bar too, (Profitec 700) and did notice a difference in body. It feels thinner, less crema, but the flavours are more pronounced and, dare I say it, tastier. I will keep going for a couple of weeks to see how it goes. Water debit, for reference, was 90g for 10 seconds @ 6bar, in comparison to 110g in 10 seconds @ 9bar.


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## Scotford

So today I decided to up our extraction a bit and see just how far I could push it whilst still being tasty as.










This was the most balanced recipe I found. No loss of body, sweet, vibrant, crisp and ohhhh that finish. So so good.

At 9bar, this just would not be possible.


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## Mrboots2u

I've hit 23-24 at 6 bar before some coffees rock there , some don't


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## Scotford

Mrboots2u said:


> I've hit 23-24 at 6 bar before some coffees rock there , some don't


But a Mythos pulling at a ratio of 1:1.7? never heard of that high and still being tasty.


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## christos_geo

I am struggling to understand why my grind size didn't need changing when going from 9bar down to 6bar with dose, tamp pressure and resulting yield and shot time remaining constant... :/


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## Mrboots2u

Has the water debit decreased ? What are you measuring the pressure by ? What machine is it


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## christos_geo

Mrboots2u said:


> Has the water debit decreased ? What are you measuring the pressure by ? What machine is it


Alex Duetto, pressure measured 6.75 bar on inbuilt gauge against blind basket so round 6 with coffee puck, although I have a gauge I fitted into a pf I can pull out of storage to check against. Will measure water debit once I get back







just seemed counterintuitive for grind not to have had to be coarsened up.


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## MWJB

Well, if you killed the shot at the same yield in the cup, you would have the same yield in the cup. Time may/may not change.


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## aaroncornish

pessutojr said:


> Very interesting. I lowered the pressure on my machine today to 6bar too, (Profitec 700) and did notice a difference in body. It feels thinner, less crema, but the flavours are more pronounced and, dare I say it, tastier. I will keep going for a couple of weeks to see how it goes. Water debit, for reference, was 90g for 10 seconds @ 6bar, in comparison to 110g in 10 seconds @ 9bar.


Report back









I have the same machine


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## MediumRoastSteam

aaroncornish said:


> Report back
> 
> 
> 
> 
> 
> 
> 
> 
> 
> I have the same machine


I've been using 6bar for a week at least now, and I am not inclined whatsoever to revert it back to 9bar. I am using Rave's Colombian Suarez, and it is just amazing at 6bar.

I must also say that naked extractions look much better.

One interesting thing though: Unless something is wrong with my grinder that the burrs moved or the coffee beans have deteriorated beyond belief (they are 1 month post roast I must say, but never had issues before) I find myself having to grind finer than usual.


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## aaroncornish

pessutojr said:


> I've been using 6bar for a week at least now, and I am not inclined whatsoever to revert it back to 9bar. I am using Rave's Colombian Suarez, and it is just amazing at 6bar.
> 
> I must also say that naked extractions look much better.
> 
> One interesting thing though: Unless something is wrong with my grinder that the burrs moved or the coffee beans have deteriorated beyond belief (they are 1 month post roast I must say, but never had issues before) I find myself having to grind finer than usual.


Thanks for the update! Job for the weekend for me then


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## Scotford

pessutojr said:


> One interesting thing though: Unless something is wrong with my grinder that the burrs moved or the coffee beans have deteriorated beyond belief (they are 1 month post roast I must say, but never had issues before) I find myself having to grind finer than usual.


There's nothing wrong with your grinder or beans. I'm grinding finer than I thought possible these days and really getting amazing extractions.


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## christos_geo

pessutojr said:


> I've been using 6bar for a week at least now, and I am not inclined whatsoever to revert it back to 9bar. I am using Rave's Colombian Suarez, and it is just amazing at 6bar.
> 
> I must also say that naked extractions look much better.
> 
> One interesting thing though: Unless something is wrong with my grinder that the burrs moved or the coffee beans have deteriorated beyond belief (they are 1 month post roast I must say, but never had issues before) I find myself having to grind finer than usual.


That was my conundrum as well and as suggested by @Mrboots2u I measured water debit which gave me 93ml/10sec @6bar and 113ml/10sec @9bar yet shots yielded same amount of coffee in the same time without modifying grind size. If anything shots fllowed a touch faster at 6bar.

Could it be because 9bar puts extra force on the puck almost slamming it against the basket resulting in a better seal, whereas at 6 bar the first few seconds resemble more of a preinfusion step where solids immediately start dissolving?

I may revisit 6bar in the future with beans I know what to expect from as I was getting shots that were almost uncomfortably bright and thought it must be pressure related. Should have gone finer.


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## Mrboots2u

christos_geo said:


> That was my conundrum as well and as suggested by @Mrboots2u I measured water debit which gave me 93ml/10sec @6bar and 113ml/10sec @9bar yet shots yielded same amount of coffee in the same time without modifying grind size. If anything shots fllowed a touch faster at 6bar.
> 
> Could it be because 9bar puts extra force on the puck almost slamming it against the basket resulting in a better seal, whereas at 6 bar the first few seconds resemble more of a preinfusion step where solids immediately start dissolving?
> 
> I may revisit 6bar in the future with beans I know what to expect from as I was getting shots that were almost uncomfortably bright and thought it must be pressure related. Should have gone finer.


What brew ratio where your bright shots ?


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## christos_geo

Mrboots2u said:


> What brew ratio where your bright shots ?


18g in 38g out ~29sec 94.5°C. Was using Ethiopian Hunkute from Rave which having tried at 9bar seemed far more mellow at same ratio. Even 40g out didn't quite balance out.


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## Mrboots2u

christos_geo said:


> 18g in 38g out ~29sec 94.5°C. Was using Ethiopian Hunkute from Rave which having tried at 9bar seemed far more mellow at same ratio. Even 40g out didn't quite balance out.


I wouldn't be afraid to go finer and push past 30 seconds ... but also going to 42g might also help

As you say having some beans that you can sense check is a good idea ...


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## matisse

christos_geo said:


> That was my conundrum as well and as suggested by @Mrboots2u I measured water debit which gave me 93ml/10sec @6bar and 113ml/10sec @9bar yet shots yielded same amount of coffee in the same time without modifying grind size. If anything shots fllowed a touch faster at 6bar.
> 
> Could it be because 9bar puts extra force on the puck almost slamming it against the basket resulting in a better seal, whereas at 6 bar the first few seconds resemble more of a preinfusion step where solids immediately start dissolving?
> 
> I may revisit 6bar in the future with beans I know what to expect from as I was getting shots that were almost uncomfortably bright and thought it must be pressure related. Should have gone finer.


yes and no, unless you have a a slow ramp of pressure or a definite pre-infusion then it wont act the same, it also shouldn't change the start of the dissolution process, although i believe that it affects the rate of dissolution during brewing.

the lower flow will facilitate a more uniform flow through the puck though, which "may" lead to less fines migration (we're looking into this) and hence less of a resistance at the bottom of the puck.


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## Mrboots2u

When you look at the stuff on low pressure as described by Matt north , they are using flat six bar - no slow ramp - just 6 bar ...

I seem to vary between flat 6 bar at the mo and looking 20-30 seconds pre infusion followed by 6-8 bar . With the longer pre infusion shots I'm grinding as fine as possible - traditional shots times have gone out the window with there at a 40-60 seconds


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## matisse

Micheal was using a flat 6 on his Gb5, I've got a Strada Ep, running a ramp up to 6 over 12secs, then a ramp down over 48 secs.

Current recipes are all in the 1:2.5 / 1:3 range and 36-46 secs.


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## MediumRoastSteam

Couple of days ago went back to 9 bar. Both my wife and I were finding that the espresso was bitter than usual at 6bar. :-(


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## Phobic

digging up an old thread, interested to see if people are still at 6 bar or not, what conclusions have been drawn in the past few months?


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## Phobic

on the basis of advice in another thread I changed to 6 bar and must say that I've noticed a big change instantly, rounder flavours, less harsh and I'm able to grind finer.

still early days but very good so far.

it's was very easy to do with a rotary pump machine, just a screw to change the pump pressure.


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## Scotford

Been as low as 4 and not looked above 7 since getting low.


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## Scotford

Just thought I'd elaborate a bit on the previous (with a tonne of caveats):

6BAR pressure is where I keep our PB on a day to day basis. If we can't make a coffee sing using either a M1 or EK and that pressure, then here is something seriously wrong. If I'm running EKspresso, I'll not go higher than 6 now, as (I've found), the lower the pressure, the more even and higher the extraction. And you can really push the EY at 7 and below. With a huge set of flat burrs on your grinder. I tried low pressure with a couple of smaller sets of burrs (Major, SJ, Anfim) and actually got more muddled shots across the board so I feel that there has to be something there. I'd like to explore this more but time is not something I have in abundance these days.

Obviously I read THIS and THIS blog posts a few times and did my own research into it before coming to any conclusions but coming to my own conclusions: EY%s are up, channeling is down, shot times are more uniform and more importantly than any of those, tastiness is increased on *everything* we put through our machine.


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## Dylan

I've not changed the pressure down to 6 bar on my machine, but since changing the Gicleur to .5mm my coffee has had a huge jump in consistency. Where as before I would be putting up with a coffee that wasn't great maybe 30-40% of the time, now it's rare I pull a bad one.

The smaller gic slows the pressure ramp up causing 4 bar of back pressure until the pressure builds at the puck beyond this, I haven't felt the need to drop the pressure as well but I might give it a spin at some point.


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## Phobic

Scotford said:


> Just thought I'd elaborate a bit on the previous (with a tonne of caveats):
> 
> 6BAR pressure is where I keep our PB on a day to day basis. If we can't make a coffee sing using either a M1 or EK and that pressure, then here is something seriously wrong. If I'm running EKspresso, I'll not go higher than 6 now, as (I've found), the lower the pressure, the more even and higher the extraction. And you can really push the EY at 7 and below. With a huge set of flat burrs on your grinder. I tried low pressure with a couple of smaller sets of burrs (Major, SJ, Anfim) and actually got more muddled shots across the board so I feel that there has to be something there. I'd like to explore this more but time is not something I have in abundance these days.
> 
> Obviously I read THIS and THIS blog posts a few times and did my own research into it before coming to any conclusions but coming to my own conclusions: EY%s are up, channeling is down, shot times are more uniform and more importantly than any of those, tastiness is increased on *everything* we put through our machine.


Great to get this longer term feedback - I read those blog posts a while ago but think it's worth a re-read as I remember them being quite interesting.


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## Phobic

Dylan said:


> I've not changed the pressure down to 6 bar on my machine, but since changing the Gicleur to .5mm my coffee has had a huge jump in consistency. Where as before I would be putting up with a coffee that wasn't great maybe 30-40% of the time, now it's rare I pull a bad one.
> 
> The smaller gic slows the pressure ramp up causing 4 bar of back pressure until the pressure builds at the puck beyond this, I haven't felt the need to drop the pressure as well but I might give it a spin at some point.


Having just done both quite close together I think the 6 bar change might make the biggest difference (although I only had 4-5 drinks with the gic only), certainly worth doing it if it's easy.


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