Hello,

In the last month I noticed that the pressure always reaches to 9 bar and even a little more, but it always drops gradually along the shot and stabilizes at about 8.3 bar. I tried adding coffee, grinding finer, but it seems that no matter what I do the pressure always settles at 8 bar. The shot is perfect and there is no channeling, I have no idea how to fix this.

I would appreciate any advice!

This is totally normal.

As the shot progresses the water "extracts" the soluble compounds from the coffee leaving less of the puck to resist the water pressure. Pressure will naturally drop and flow rate will increase.

One of the common uses for a flow control is to slowly close it as the shot progresses and the puck becomes less resistive, accentuating the declining pressure profile.

Agree with above. This is completely normal. If the shot is perfect and there is no channeling, there isn't anything to fix. Just enjoy your espresso and stop worrying.

I too agree with the above "puck erosion" concept. If you are worried about the machine itself, simply place a blind screen in the PF and make sure the pressure holds at 9 bars or whatever pressure the OPV is set to.

PIXIllate wrote:<snip> One of the common uses for a flow control is to slowly close it as the shot progresses and the puck becomes less resistive, accentuating the declining pressure profile.

I totally agree with Chris & Alan; it's normal. The FCD manometer also useful in another way. I used to watch for blonding of the shot, as a guide as to when to stop the pull. But I always found that it's hard to discern exactly what colour blonding is. With the FCD manometer, one can watch the pressure drop as the puck erodes, as noted. Once it stabilizes, you now have a much more visible and repeatable data point to gauge when to stop the pull.

Thank you for all the comments!

I uploaded a video that I hope will accurately illustrate the pressure during brewing.
You can see that after 20 seconds the pressure suddenly rises for some reason.
I just can't figure out why it can't stay on 9 bar no matter what i do.

I would greatly appreciate knowing if you think it looks normal and if not then what can be done to address the problem.

Thanks!

If that is with a blind filter then yes, that is perfectly normal behaviour. The brew path is totally blocked therefore the pressure will remain at the value you have the OPV set to.

A coffee puck, on the other hand, only totally blocks the brew path at the beginning of the shot. As the water works its way through it carries parts of the puck with it into your cup (coffee). Therefore it is a less and less complete seal and the pressure begins to drop.

To be clear this is a good thing. A declining pressure generally tastes better and many people (myself included) use a maximum pressure of 8 bars or even less.