Secrets to Perfect Espresso: Pressure
Pressure is one of the most important variables when it comes to brewing flawless espresso; too much and the espresso will be too gritty, not enough and it will be watery. There are actually two facets to the pressure equation: tamp pressure and brewing pressure. Tamp pressure refers to how tightly the grounds are compacted in the portafilter of your coffee makers. A good starting point is 30 lbs of pressure, but you can obviously adjust this to your particular taste.
When it comes to the brewing pressure, you should shoot for about 8 to 9 BAR of pressure—about 135 PSI. Most machines have this built-in already, so you probably won’t have to worry about it. Some machines advertise that they can brew at higher pressures, but this really isn’t necessary and will not improve the quality of your espresso.