I opened up the light roast this morning and pulled a shot. And later, when I went to clean out the basket, lo and behold there was that dark ring down around the bottom outside of the puck. Right where there are no basket holes.

If it weren't so tricky to drill 0.3mm holes in steel I would think it would be interesting to buy a second basket and add some holes.

phildawes wrote:Agreed, I am really pleased with the shots I get from the Robot. This is mostly just curiosity (and maybe the potential to improve even further!)

Your statement here is the most important thing. This prior Home-Barista post also discussed the darker periphery and mitigation strategy. Improving light roast espressos with the Cafelat Robot

FWIW, on the rare times I check the spent puck, I always have the darker periphery as in your OP w/o use of paper filter. In unblinded testing and small sample size by myself, using bottom of PF paper filter I did get less dark periphery on spent puck. But there was no appreciable in-the-cup benefit to my novice palate. For curiosity sake I should try same testing with more experienced (palate-wise) HB members.

I'm brewing hybrid quick shots with Tim Wendelboe coffee (both "filter" and "espresso" roasts**) and have noticed this dark ring as well. Because I began adding paper up top now, too, maybe that's the reason, so I tried without and no difference. It's probably related to the basket taper at the bottom.

** I can't smell or taste a difference between the two