I shall precise that I am using a Elektra Microcasa a Leva (MCAL), so a spring lever machine, and my question seems more related to these type of machines (see What difference in taste between grinding finer and tamping harder? for related discussion).

When the flow is a bit too fast (and you don't want to modify the dose), two choices are possible with a spring lever machine:
1) grinding just a notch finer ;
2) tamping harder (assuming you were tamping rather light to get this fast flow)

With the MCAL, I experience that changing tamping pressure from 15lbs to 33lbs decreases the speed of the flow (therefore changing the result in the cup) more or less similarly than by keeping the same tamping pressure but grinding 1/2 click finer on my Commandante C40 (with Redclix).

Will the two possible modifications above affect similarly or differently the result in the cup?

tamping should not make a difference in flow rate, unless you tamp too light to start with. Can you explain what you mean with 7 to 15 bar of tamping?
Tamping can be measured using a pair of scales, anything over 5 kilo is enough

Dose and grind setting are usually what is used to control flow rate, not tamping pressure.

StefanoB wrote: With the MCAL, I experience that changing tamping pressure from 15lbs to 40lbs decreases the speed of the flow (therefore changing the result in the cup) more or less similarly than by keeping the same tamping pressure but grinding 1/2 click finer on my Commandante C40 (with Redclix).

Will the two possible modifications above affect similarly or differently the result in the cup?

You yourself are in the best position to answer this question. You now have an experimental set-up which will allow you to pull a number of shots by each method, and to compare the results - blindly if possible. I, for one, look forward to hearing your conclusions.

Marcelnl wrote:tamping should not make a difference in flow rate, unless you tamp too light to start with. Can you explain what you mean with 7 to 15 bar of tamping?

Yes sorry, it was a mistake (should be kgs not bar). Now I have corrected that and put numbers in lbs.

I use a calibrated tamper where 3 different springs could be used: a 15lbs, 22lbs and 33lbs spring. Oddly enough, I experience some measurable variation of flow when I change spring (everything else being constant)...

mathof wrote:You yourself are in the best position to answer this question. You now have an experimental set-up which will allow you to pull a number of shots by each method, and to compare the results - blindly if possible. I, for one, look forward to hearing your conclusions.

Thank you for answering. I was asking because I thought it would be something very well known. The answer I got from another topic, is that tamping pressure should not change flow, but although this is most certainly true for pump machines this not what I have experienced so far with my set up (MCAL and C40). But maybe I'm wrong, and like the previous poster says the variation of flow I observe come from small variation of water temperature from shot to shot.

So I'll experiment more, and come back if I can draw rock-solid conclusions out of many experiences for this question.

With my current roasts I only polish the puck.
This may be of some help:
Using built-in tamper on grinder (example: Mazzer Mini)

Interesting article:

https://www.baristahustle.com/blog/how- ... -you-tamp/

So I should stop with too lights tamps. They don't give numbers, tough, about this minimal tamping pressure to get consistency.

There is also this video:

http://www.youtube.com/watch?v=9l0dnXHM1cU

At 2:00 and onward we can see shots run in parallel, where only the tamping force (from 5 lbs to 40 lbs) varied. Above 20+ lbs time of the shot remains virtually constant.

StefanoB wrote:....

So I'll experiment more, and come back if I can draw rock-solid conclusions out of many experiences for this question.

You must have a laboratory then.
If your remark that the flow rate is too fast is based upon tasting the espresso (imo that's the thing that counts) you have more options then only adjust grind setting.

Though grinding finer would be the option to start with.
Group head temperature is something to keep an eye on and to experiment with.
The 3rd one is changing the ratio.
These can all be adjusted without changing the dose.

StefanoB wrote:Thank you for answering. I was asking because I thought it would be something very well known. The answer I got from another topic, is that tamping pressure should not change flow, but although this is most certainly true for pump machines this not what I have experienced so far with my set up (MCAL and C40). But maybe I'm wrong, and like the previous poster says the variation of flow I observe come from small variation of water temperature from shot to shot.

So I'll experiment more, and come back if I can draw rock-solid conclusions out of many experiences for this question.

Yes, you are right, probably the pressure tamp don't change the flow in a pump machine, I have a Flair Pro 2 manual espresso and the different pressures in tamp change totally the flow of the shot, I use a really hard tamp that allow me to make long pre-infusion without drops of coffee falling from the screen, when I ramp slowly to the 9 bars extraction I have the stream in the screen, for me is best to have a hard tamp to remove one of the variables in the different shots, I tamp hard always and I have consistent shots always.