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a 22g dose
That seems like a massive dose. Is there any chance you're over-filling and when you put the portafilter in and rotate, the puck is rubbing against the shower screen?
I understand that I should be in the 20-30 second bracket.
Yep, I normally aim for around 26-28 as a starting point then go from there using taste
My thinking is to tamp with more pressure to slow the extraction.
Likely won't make much difference as the water will be exerting more pressure anyway. Any chance the tamping isn't level so you're getting channelling down the side? Or are you knocking the portafilter with the tamper to get grounds of the side? That can also cause channelling by cracking the puck.
Finally got around to buying a scale and has confirmed my suspicions that my extract is too fast. I'm using Pact coffee, pre-ground to 'fine' for espresso use.
This morning, aiming for a 2:1 ratio, a 22g dose yielded 45g in around 16 seconds - I understand that I should be in the 20-30 second bracket.
My thinking is to tamp with more pressure to slow the extraction. After that, I'm really not sure...