hollywood87 wrote:Freshest coffee beans
Espresso fine grind with Burr grinder
Strong tamper vs. light tamper
Different amounts of coffee (ranges from 12g to 17g)
Heating up short time vs long time
Realeasing steam after heating
Pouring a cup of water before extraction
Lifting lever slowly up and lifting faster
What kind of beans? All arabica? Light roast, dark roast, medium perhaps? To start out, my recommendation is to use fresh medium roast. Just easier to work with.
Again, to start, just choose a dose that just about fills your basket and keep it until you get success. Change grind size to get the flow you want.
Heating up is important. You should get some type of grouphead thermometer such as temp strips (Flair strips are good I hear). Brew when at around 85 celsius if millennium model.
Releasing steam after heatup is good. Keep that.
IMHO, with millennium machines, flushing water out is not that good but you can do a quick flush.
Lever is lifted very slowly. Infact you could lift it without the portafilter in until some steam/water is released, stop the flow, and then lock-in and lift. Search "late lock-in".
Lastly, and most importantly, which burr grinder? Grind is the most important part here and a badly aligned or otherwise misbehaving grinder will make all other efforts futile.
When grinder is sorted work on your preparation, including WDT and possibly RDT.
And only change one parameter at the time.