Note that a variation of only 2° (3.6') may cause your espresso to be either too strong or too weak.
the pressure produced by the expresso machine must be equal to 9 bar (less is not enough to make a good espresso, but a higher pressure can be equally damaging to the quality of your espresso).
the espresso should take 25 sec to be ready. Five seconds more or less may result in a coffee that is either too bitter or insipid.
coffee must be grinded fine, but not too fine. The commercially pre-grinded coffee for espresso machines usually has the correct ground. Coffee grinded on demand, like in some coffee shops, is sometimes grinded too fine. The ground should be nearly powder-fine but not as fine as icing sugar, for example. If the ground is too fine, the coffee will migrate together with the water and produce a coffee similar to a turkish coffee (where you have to wait untill the coffee ground settles to the bottom of the cup before you can drink it !) instead of an espresso.
How to make a real italian coffee with an espresso machine?
use about 25 cc (1 tb spoon) of ground coffee per cup and press the coffee down lightly and evenly. Again, if pressed too hard the coffee may become too strong; if not pressed enough, it will be too weak.
