These are some personal opinions, so take them as such and not as some hard-and-fast rules.

For medium or medium-dark ("espresso blends"), I seemed to find between a week and three weeks from roast to provide better results than coffee that was only a day or two from roast, or over three weeks old. This assumes that the bag is heat sealed from the roaster, not just a roll-top with a wire tie. I usually tried to finish a bag within a week of opening it. Keeping it in a sealed container, on the counter, out of the sun and the heat is probably fine for most people and their coffees.

Learning sour, bitter, and astringent is tricky. It's especially so as you often get two or all three at the same time.

I think that learning how your grinder, coffee, and espresso maker work together is valuable, even if it means "wasting" a few shots. I find that keeping a notebook of the shots I pulled helps me see patterns easier. Even a brief description of flavor, without all those fancy fruits or chocolate/nut variations is useful. "Yuck, ash tray" tells me what I need to know when I'm scanning backward and see that last time it tasted like this, it was 3 clicks looser (for example) and I got to "OK, still a bit bitter".

One thing is to let the espresso cool a bit. Maybe even a lot. When it is hot, all you can taste is hot. Some people say that espresso gets bitter as it cools. My belief is that theirs was bitter all along, they just couldn't taste it when it was so hot.

You might try intentionally adjusting both up and down two or even four clicks from where you like the taste†. That way you get a feeling for how much and what kind of change those make. You may be able to feel the difference when you pull the shot, not just in the taste in the cup. You don't have to drink them all down, but let them cool some and taste before you dump them in the sink. Even if they're tasty, you may not want to try more than a sip or two so you don't get too jittery.

As for Sprometheous, that video left many of us wondering. As I recall, he only had the Robot for a short period of time, had problems using it, which his friends said was "puck lift". I don't think anyone here figured out what puck lift was, or how it could possibly happen with any sensible use of the Robot. True, if you're "shaking hands" with your Robot and the arms are waving like Robbie, "Danger, Will Robinson, Danger!" you're likely to displace the puck, but ...


† I don't have my JX-Pro with me, but I vaguely remember 4 clicks to the number. The goal is to make a change that is enough to push you away from the sweet spot a bit, without getting into a complete gusher or something that takes two minutes to press through.

It seemed Sprometheus just didn't understand how pre-infusion works and was given a bogus theory in an effort to explain what he was experiencing. There is some merit to coarsening up the grind as a way to increase extraction, as explained in this article: https://www.cell.com/matter/fulltext/S2 ... 19)30410-2 (or just look up turbo shots)