AMzf wrote:when I make my espresso, one of my friends says it is always bitter taste
FWIW, I'm more than a bit puzzled by a request like this from someone with a world class machine (assuming I'm reading correctly that you have a Sanremo Opera V2
). I'll suspend disbelief long enough to try to help...........once.
The first question is how it tastes to you
. If your friend thinks it's bitter but you don't, your espresso may be fine and your friend may be the one with the problem. If you think it tastes fine, go with him or her to have a few shots made by others and see if you agree on them. Then you'll know if you have anything about which you should be concerned. If your espresso really is bitter and you can't identify anything that's clearly wrong (like stale beans, a brew temp that was accidentally set too high, etc), there are so many possible reasons that it's usually easiest to go back to the beginning and start over. Everything from fresh beans and good water to a completely spotless machine can matter - even failure to fully clean your baskets and PFs can result in bitter taste.
I don't understand how (or why) you're using "water from a supermarket" in a Sanremo Opera - I can't imagine that it has a reservoir or that you're feeding it from a jug. But if you really have one, you must know something about espresso because that would be a very, very
unusual machine for a novice. From what I've read, it has multiple boilers, fluid paths, pumps etc so that everything imaginable is adjustable or controllable during every millisecond of the entire brewing process. Trying to change and balance so many variables without a plan is as likely to make things worse as it is to make them better, if you don't know what you're doing. Your espresso may be off because you have much too much to set and no way to know where to start. It is, however, very hard to imagine how you got this machine without benefit of any support or knowledge about it.
So assuming you do have an Opera and truly don't know how to use it, go back to the beginning and set basic brewing parameters like temperature and pressure as though you were using an ordinary machine. Use the temp and pressure recommended by whoever roasted your beans, without profiling of any kind. In short, turn it into the functional equivalent of a Silvia for a few days and learn to pull a simple decent shot, if what you're making now is not good.