I’ve been using my Rancilio Silvia with my Eureka Mignon Manuale grinder to pull two double shots daily for about a year now. I’ve been working really hard to maintain consistency with my distribution and tamping, but the one thing that has been consistent is how uneven the extraction is.
Nearly without fail when the coffee first emerges from the bottom of my bottomless portafilter, it emerges from back to front, and blondes much faster at the back then at the front. I know this is causing uneven extraction and unnecessary bitterness. What could be causing this, and how can I improve? Is it something intrinsic to the machine or am I habitually tamping crookedly? How can I diagnose?
Regardless of the actual cause of the problem, if its consistent, you have a clear route to a solution–make the back have more resistance. You could certainly do this in your distribution and your tamp, and while a bad habit normally, it’d just be an adaptation to your situation.
Regarding cause, I have a feeling if it was your tamp, you’d have noticed by now just from paying close attention. Once tamped, but before the tamper is removed, you should just be able to examine the tamper visually to see if it’s level. This is a little easier than trying to tell if the surface of the puck itself is.
If its not the puck, then its probably a quirk of the machine.