Some time ago, I bought a moka pot in the hope of producing coffee that more closely resembled espresso. And using good coffee, and experimenting with technique, I have produced some very rich, nicely-balanced extractions. However, I have been able to reduce, but never fully remove, some underlying burnt notes in the coffee produced. This problem has led me to ask myself about the nature of the moka pot design itself.
Water in the chamber is heated and the vapour inside trapped. Once the vapour pressure in the chamber is great enough, it forces the heated water up the spout, through the coffee charge, and into the collection chamber. My experience has led me to ask: is the heat required to produce adequate vapour pressure is not inherently higher than the ideal, hence predisposing the moka pot to producing bitter or burnt coffee?
This also raises questions about best practice in moka pot coffee extraction. It would suggest that the best extraction would be when ambient air pressure is lower, the coffee charge is not tamped, the water is heated gradually, and the water is not fully consumed (i.e. the extraction is terminated before the water in the chamber is gone).
My own experimentation would tend to confirm the notion of not tamping the charge, but I have had limited success associating technique with outcomes.
Have any objective measurements been made with regard to the temperature and pressure inside a moka pot, with the charge tamped or untamped? And how do those measurements compare with the theoretical ideals for coffee extraction?
Thank you in advance.