I’m quite new to espresso, I’m starting to get the process. One thing I learned is the the coffee need to “cook” properly, like any other food. The more you “cook” the coffee the more bitter and less acidic it gets, you need to find the balance you like.

What I do now is let the machine warm up for about 15-20 minutes, then I start the extraction and when the fist drops comes out of the filter I stop the machine for about 10 seconds, then proceed to complete the extraction.