To prepare an espresso requires lot of precision and know-how from a good barista. The coffee is always ground just before the extraction.
The recipe for a perfect espresso (30 ml) goes as following:
- Pressure applied to tamper: 20 kg
- Amount of coffee: 8-10 g
- Water pressure: 9 bar
- Water temperature : 92 °C (between 88 and 96 °C)
- Extraction time: 20-28 secs
- Coffee grounds after extraction: An almost dry and solid puck with little residu left in the portafilter.
If your espresso takes more than 28 seconds to extract, your grounds are too coarse. Tighten the burrs and readjust your grinder. You could also try using a bit less coffee. If, on the contrary, your coffee takes less than 20 seconds to extract, grind a finer and/or use a bit more coffee.
The « crema » : A good espresso should have a beautiful layer of uniform, bright, non-striped foam on top, thick enough to last 4 minutes.
The cup should always be preheated and it's sides should be quite thick in order guarantee a good thermal isolation.