My experience of making espresso based coffees with an amazingly well informed and experienced barista. There are so many nuances that make a great cup of coffee that it's hard to pin it down. I used the same fresh beans, same machine, same water etc etc and his coffee tasted a world better than mine because he had the timing and technique to making down. He explained and demonstrated that even small things like how densely you pack the coffee in the filter basket makes a considerable difference. It was an eye opening experience.
Some coffee houses have pressure limited tampers to heko ensure every coffee is the same regardless of who is making it. Everything has an impact, size of grind, water pressure/temp, freshness, and then the myriad of little things. One of my pet peeves is watching the barrista attach the coffee handle and leave it there whilst finding a cup/faffing all the while the coffee sits next to a hot plate and gets ruined :(
Not really. Brew temperature, extraction time, tamp pressure, bean freshness, all have a measurable impact on crema, bitterness, etc. there are many variables which combine to form a good cup, or a bad one. This is not the same as saying there's some mysterious magic to a good espresso.
