What is difference between pressure profiling and flow profiling

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Disclaimer : this is NOT our original text, following extract is from thread by forum named  home-barista.com
I still do not understand what is the difference between pressure profiling and flow rate control.
Correct me if I am wrong, but from my understanding, the pressure the pump generates affects the water flow in espresso machine.
In other words, the 9 bar pressure generates different water flow with 7 bar pressure.
So, if we create pressure profile to brew espresso shot, we also create flow rate control.
Or am I missing something here?
For the simple answer, pressure profiling and flow control are two methods of achieving the goal of extracting everything you want from the coffee.
The fact that when using the flow control devices designed for the E61 head, the user is monitoring pressure while controlling flow is the proof that the two are so closely related.
The fact that the coffee in the basket is changing as the brew cycle progresses means that the extraction characteristics are changing.
Most obviously the coffee “blooms” once it’s dampened with a pre-infusion at extremely low pressure and flow, the grounds swell up and fill more volume in the basket.
Then, of course, after the first part of extraction, a lot of the coffee oils (and some solids) have been carried out of the puck, the puck becomes less resistant to flow, a machine that will restrict the available pressure or flow nearing the end of the extraction time is accounting for this pressure-drop across the puck.
I hope that kind of answers what you were looking for.
Flow control by way of a needle valve restricting flow to the brewhead is one way.
Pressure control by way of a needle valve relieving some flow before the brew head is a common modification.


(A) With few exceptions, the marketing terms are, at best, imprecise. Most “flow control” devices don’t directly control flow.

(B) Changing one changes the other during extraction.

Pressure and flow through the puck are tied together in a relationship based on the condition on the puck and basket as the moment.

You can control pressure applied to the basket as the unit and the flow will change as the output.
A handful of machines meter flow into the basket.
With these, pressure responds.
E61-style and other valves add resistance upstream of the basket.
The knob setting is not “flow” or “pressure” as how much the pressure is reduced for a given flow.
It will vary with flow, more with higher flow, tapering off to none with no flow.

This video is one of the more detailed, useful discussions I’ve seen on the concept. One caveat: does flow or pressure profiling actually deliver better espresso – that’s a much longer, drawn out discussion, with mixed opinions. :P



#5: Post by Castillo2001 »

Jeff wrote:TL;DR

(A) With few exceptions, the marketing terms are, at best, imprecise. Most “flow control” devices don’t directly control flow.

Care to expand? I have an ECM with the flow control kit. The valve does control the flow of water, if I have it 1/4 turn open it only flows 2.25grams per second, but at 1 turn open it flows at 9grams per second. I believe this is the same overall design of most of the E61 flow control devices.

As far as I understand it:
Flow control is some type of device, normally a valve that controls the amount of water that flows thru the system. This does directly impact the pressure but you are not actually controlling the pressure but the amount of water flowing.

Pressure profiling is when you are control the pump pressure, such as a DC pump that you can control the voltage thus increasing or decreasing the pressure the pump is creating.

This impacts the flow of water but you are not directly controlling the amount of water flowing.

As for the question of does this help with the quality in the cup. For me it does, as an example I had a medium light roasted Kenya that was bright and fruity. My wife doesnt usually care for that type of bean. Using the Flow control I was able to bring the brightness way down and the fruitiness to a level she enjoyed, while using a different flow to pull my shot that kept the brightness. I was able to do this using the same grind setting which means I can pull two different shots that are enjoyable by me and then my wife without making any change to the beans, grind or dose. Simply moving the little knob differently for each one.

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Team HB

#6: Post by another_jim »

Does your water faucet valve affect the flow or the pressure? The answer is yes. Does the water pump that supplies your house affect the flow or the pressure? The answer is yes. I won’t comment on the sense of asking either or questions like this except to say: either take a physics course or accept that water faucets and water pumps can both work as controls.

Far more important than the question of whether a valve or variable pump/piston are used, is the question of how well designed the ergonomics are (i.e. is it smooth, finicky, rough, time-lagged, intuitive, engaging, etc,), and whether the control is via programming, via manual control during the course of the shot, or both.

Jim Schulman
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BaristaBoy E61

#7: Post by BaristaBoy E61 »

I imagine that flow and pressure are inextricably linked as voltage and current are to power as measured in watts, where flow would be like voltage and pressure would be like amps except there may not for espresso be a formula that represents it as clearly as does Ohm’s Law for electricity.
“You didn’t buy an Espresso Machine – You bought a Chemistry Set!
I asked the same question a couple months ago and I had some very helpful answers. TL;DR is that a designer of an espresso machine can chose to use either a pump or a valve to achieve pressure profiling, with pros and cons for both.
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#9: Post by Peppersass »

When there’s enough resistance in the system to cause pressure to be greater than zero, changes to pressure will affect flow and changes to flow will affect pressure.

When pulling a shot, this state is reached when the puck is saturated and the basket is filled with water. The puck resists the flow, causing pressure to rise and flow to decrease. As water passes through the puck, propelled by the pressure, the puck becomes more permeable and the flow increases. If you have a pump with a bypass valve, it will hold the pressure constant at the preset value. Same pressure, less resistance, and greater flow. If you have a pump without a bypass valve, pressure will decrease as the flow through the puck increases. Less pressure, less resistance, and greater flow, but not as much as when pressure is held constant.

For the most part, when you see “flow control” being discussed, people are talking about slowing the flow during preinfusion. When you see “pressure profiling” being discussed, people are talking about changing the pressure and flow as pressure is rising in the basket and/or after peak pressure has been reached.

A modest amount of flow reduction as the machine ramps to full pressure can help prevent the puck from breaking up, which it might do if slammed by a powerful flow of water. Many manufacturers put a flow restrictor, or “gicleur” between the boiler and group to reduce the flow during preinfusion.

Further reduction in flow during preinfusion can aid in extracting light-roasted coffees. Often these coffees are difficult to extract, and if you try to grind them really fine to get more extraction you’ll choke the machine. But if you grind really fine and slow the flow rate during preinfusion, the water has time to gently open up the puck before it gets compressed by full pressure. This lets enough water pass through the puck to avoid choking the machine. Typically, these shots run longer than traditional shots, so extraction is aided by grinding finer and longer contact time with the hot water.

After the basket becomes pressurized, you can regulate pressure or flow. Changing either will affect the other. A common practice with light roasts is to reduce pressure and flow after maximum pressure has been reached in order to slow down the natural increase in flow rate that occurs as the puck becomes more permeable. This increases contact time with the hot water, potentially increasing extraction. You can do this with a variable speed pump or a valve.

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BaristaBoy E61

#10: Post by BaristaBoy E61 »

Thank you Dick for the most comprehensive explanation I’ve read to date.
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