Taste preferences are subjective and what one person finds enjoyable might not be enjoyable to others etc.
However, as a general guideline, for the most part most people agree that underextracted coffee tastes sour, almost unpleasantly fruity and weak, and overextracted coffee tastes burnt and bitter.
Note that milk heavily masks the above. You’ll still get elements of it but it’s much easier to distinguish without milk. The challenge here is that some people (myself included) much prefer milk based espresso drinks and I find even some dialled espressos unpleasant.
Also worth mentioning that I’m yet to pull a shot that was undrinkably unpleasant with the LM despite having the same exact coffee extracting at anywhere from 20 to 40 seconds. It’s not down to my great skills because with the Bianca and machines before, I’d pull some absolutely vile shots if they weren’t fairly accurately dialled in.
I’m still unsure as to what it is, whether temp or pressure consistency just allowing more forgiveness but I’ve found you’ve really got to get the grind massively wrong to make a ‘bad tasting’ shot.
That’s not to say it’s not possible, of course if you pull a 38g shot in 12 seconds it’s probably going to be unpleasant, likewise if you’re only getting drips at 40 seconds or something.
Then there’s the big variable of the beans themselves and to some degree, their age.
Med-dark roasts from reputable roasters are pretty forgiving, whereas lighter roasts, especially the expensive super-light roasts can be an absolute Weston to dial in.
I appreciate the above isn’t hugely helpful. One little test could be to deliberately under extract a shot and then completely over extract another to taste what they taste like, then look out for hints of that in future when dialling in.
