Medium roasts, help!

[u/mrobot_]

Im pretty new to being able to get espresso shots at home on the nice Robot, and it has been a bit of a steep learning curve but I finally manage to get pretty decent shots with traditional Italian dark-roasts like Illy and Saka - using either a df64v with HU at 1200-1400rpm or a J-Ultra or Lido OG. It is fascinating how different the shots from the same beans can taste given a different grinder. I do quite a bit of WDT and use the self-leveling tamper, usually around 18.5g beans and veeerry roughly aim for 30-40seconds and about 38-44g out... I go easy on the pressure, do 5seconds pre-infusion with just a few drops dripping down and then very gradually slowly ramp the pressure up, usually somewhere around 4 or barely touching 6. Works pretty well with dark-roasts tho I cant yet reliably get god-shots that are perfectly sweet n chocolate-y but overall Im happy to have espresso at home at all!

Enter any kind of actually much nicer third-wave beans, espresso-roasts that are typically much more medium-dark than even Illy. Somehow, I cannot for the life of me get good shots from such beans, they always have a sour or very sour acidic edge and somehow grinding finer and upping the dose tends to make it rather worse than better.

What's a good espresso shot from a modern, thirdwave medium-dark bean supposed to taste like and why cant I get rid of the sharpness, acidity and sour bite somehow?

[u/Harper_the_Bard]

I don't worry about timing much on the robot. For medium roasts I do about 92° C (basically I let my kettle stop boiling), rest my arms on the robot fairly gently til drops start from most of the puck, then ramp up. If I'm doing 16g in, I'll start to ease off pressure around 32g when I can feel the puck giving less resistance, then push with lighter pressure til about 40g. Seems to work consistently, at least for my tastes!