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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.

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    Welcome! Great question! Just one minor remark: AFAIK, the coffee in a moka should always be untamped. Filled to the top and evened out, yes, but not pressed. Or do you have another reference? Of course this still leaves lots of parameters, from grind to extraction time.
    – Stephie ♦
    Commented May 3, 2020 at 21:59
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    Thank you, @Stephie. Yes, that has been both my experience and what I have read. (I tried tamping the charge because I like the empirical approach, but it appears to lead to stronger burnt notes. But even untamped, I have never been able to remove those burnt notes entirely, although I have never, admittedly, tried a particularly coarse grind, since I am aiming for a richer espresso-like extraction. So I suppose my question boils down to (pun intended) whether the design of the moka pot necessarily requires excessive heat to produce such rich coffee.
    – POD
    Commented May 3, 2020 at 23:08

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This is nothing I've tried myself, but to add onto your theory of the heat required to brew the Moka-Pot, I believe we'll arrive at an answer. The problem is not likely the water temperature itself, it turns out it's realistically pretty difficult to get boiling water onto coffee when using some sort of brew method (as the metal absorbs enough heat to drop the water temp).

However the lengthy heat time on the mokapot will actually heat up the ground coffee itself during brew, and this can lead to poor tasting coffee. The best thing you can do, from my understanding is pre-heat the mokapot bottom and start with hot water before assembling and putting on the stove. Additionally, as soon as the coffee starts spurting, it's done and you can run under cool water to halt brewing as well.

I got most of this info from a mokapot video I saw a while back, thought it might help you as well: https://www.youtube.com/watch?v=rpyBYuu-wJI.

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  • Thank you. That does make a lot of sense. I did try the opposite approach, heating the water very slowly with the intention of trying not to apply too much heat. However, that approach did not seem to make any difference, and if anything tended to lead to stronger burnt notes. That finding seems to support your theory.
    – POD
    Commented May 4, 2020 at 22:35
  • Let me know how it works if you get a chance to try it.
    – Tyler Hartwig
    Commented May 5, 2020 at 17:55
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Don't tamp. Tamping increases pressure requires for steam to escape due to compacting of the grinds, and that means the chamber will have to get hotter and produce a greater chance of the coffee burning.

Low and slow is the name of the game with the moka pot. You want just enough heat for steam to push through the coffee and not a bit more. Too much heat will burn grinds and will eject coffee up the spout and into your brew. You do not want a boil, so heat shouldn't be the problem.

However, how much heat is required to produce sufficient steam will depend on how much coffee you're using and your grind. Experiment with these variables (don't tamp!) to work out good values for your preferences and pot size.

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  • Thank you. That validates my own experience, and conclusion that the coffee should not be tamped. For the same reason, I can see how too much coffee and/or too fine a grind could also demand the application of too much heat and pressure.
    – POD
    Commented May 6, 2020 at 0:10

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