Brewing Courses Question About The French Press (for Brewing Coffee): What Causes Pressure Within?

Question about the French press (for brewing coffee): what causes pressure within? - brewing courses

This question may have a scientific mind, do with me.

Details: I make coffee in a press French. Immediately afterwards, pour boiling water in the French press (which has a tablespoon of ground coffee, of course), I note that the pressure of the press French based instant.

Sub-questions: What is the pressure so great that I can not get the press does, if I all my strength to use? Often he had to pull the press handle a little and (then press down again, so that the air / vapor to escape) - so the pressure decreases significantly.

Click OK, you will probably say: "Of course, this is a scientific fact. This happens all the time." But the pressure is not always accumulate so much. Perhaps some variables have a role to play (pressurized water / steam, brand coffee (or grind fine, of course, the purity of coffee, etc.?).