The tamper: often a mysterious tool located close to the grinder.
Mysterious because you can find many types and very different among each other, consequently we need to understand the purpose of this tool (not at all secondary) that many would consider as a tool for pressing the coffee: thing which is correct but how to use it and why?
We need simply to press the coffee in the filter in order to leave the surface flat, without “slopes“ that could cause a not homogeneous extraction. Indeed the water, flowing down with 9 BAR of pressure, could find easier to extract initially the part with less coffee giving a result in the cup different from the expectation. Moreover the percolation could happen at first from one of the spouts and then from the other with the consequence to get two different cups also in the aspect.
How many Kg of pressure do we need to apply?
Scientific studies tell us that impact on the extraction of a pressure between 12 and 20 Kg is negligible.
Suggestion: to regulate yourself it’s enough a normal scale, locate it and simulate the pressing with the tamper.
Which is the correct position to use the tamper?
I could summarize it this way: position yourself with the pelvis in parallel to the filter holder, tilt the filter holder until you assume a posture with straight shoulders, locate the tamper inside the filter in a horizontal way with the fingers at the turn of the filter edge and the tamper, straight wrist, press with the finger helping yourself with the hand palm.
Suggestion: don’t look at the tamper while pressing, it helps not to get confused.