Here's a thread that's been percolating for some time (sorry):

I wasn't sure whether to post this here, or under "Coffee" or "Levers" or "Grinders", etc. To me, this post is sort of all-encompassing, touching on many things I've pondered and posted about before. It's sort of a status update of my espresso experience. I hope it's helpful to others, even if our set-ups are different.

It may also come down to, "Am I using the 'right' coffee?" (Ecco's espresso blend).

First, a little background:

After years of honing my technique on my millennium-era pavoni euro, I feel I'm operating well. Thanks in large part to this site, as well as others, and to constant practice and adjustment, I have discovered that the machine has greater capability than I realized when I began. Just as one minor example, when I started, most of what I read -- and my experience confirmed -- said that a "1 pull double" was pretty much impossible with this machine, that to get 1.5-2oz, you had to raise and lower the lever at least twice. I have found that with the right dose and grind, you can, in fact, get a "traditional double" from one pull. Repeatability is ever-elusive with this machine, but my shots, usually in the 1.5oz area, look and taste good, especially in capps.

I finally bit the bullet a few months ago and upgraded to the Vario from a Gaggia MDF. Really does make a world of difference. Thanks again to all who encouraged and supported my decision.

My problem is that my capps are great and elicit oohs and aahs from friends. But my straight shots still often have a little bit of bitterness at the end of the sip. I know there are those who feel that that's one of the characteristic tastes of espresso. I also know that the 3rd wave and hobbyists have shown that that is not a given.

Obviously, to each, his/her own. I don't mind some acidity, but I also enjoy drinking a shot that's strong, yet smooth. You know how when you brew a really good cup, whether it's pourover, press, drip, etc., it can be strong, but not bitter at all? I find this rarely happens with my espresso shots.

I can't post pics, but my extractions generally look really good, not over, not under, no blonding...

I don't have a bottomless pf. Maybe Ecco isn't suited for this machine, though I don't think that's the case.

Any insights would be greatly appreciated. The better I get, the more frustrated I become! But I know that's another subject. Thanks.

Hard to say but did you try lowering the temperature. You should have a nice acidity and sweeter balance, no bitterness.