Grinding is an important stage. There are two types of commercial grinding-dosing units:
• flat grinders are the most common and, as their name suggests, they have flat grinding blades rotating at 1400 rpm. They need to be checked every 300 kg coffee;
• conical grinders with blades rotating at 4/500 rpm (much more expensive). They need to be checked every 600 kg of coffee.
The objective of both systems is to grind coffee beans into an even powder, suitable for infusion, which is neither too fine nor too coarse, bearing in mind the humidity that affects yield (the distance between the blades can be set for finer or coarser grinding as required).
The operating temperature of the grinding-dosing unit must never exceed 40/50° to avoid affecting coffee yield. This, essentially, is the difference between flat and conical blade grindingdosing units: the former rotate more rapidly and risk overheating more quickly and are thus unsuitable for heavy-duty espresso coffee service.
The “espresso” system produces a very particular drink, with a layer of cream – the foam produced by the emulsion of particles of air and coffee oils – a distinct body and an extraordinarily intense aroma thanks to very efficient extraction; the creamy layer itself also prevents all the finer qualities of good quality coffee from evaporating.