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Well the moka pot itself didn't explode, rather the coffee bursted out from the funnel of the collecting chamber and through the middle of the moka pot, splashing all my clothes and half of my kitchen with coffee stains (nobody got hurt). Before the explosion, the coffee was sipping through as usually very slowly and there was no sign at all of any pressure building up or that any explosion was about to happen.

For this brew I had used a very fine fresh grind and almost boiling water. I had also cleaned the whole moka pot beforehand, as a I do every time.

What could have caused this and what can I do to prevent such an accident from happening in the future?

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    This happened to me once, and when dismantling I found that I had put the filter-plate in upside down. Whether or not that was the cause, or just a coincidence, I have no idea, so I won't put this as an answer.
    – cdmackay
    Commented Jul 28, 2016 at 18:50
  • This happened again to me today. I dont understand it. I always rinse it through 💯 and the water is always below your red line. What do you mean by ‘valve’? There’s nothing to ‘press out’ on my unit
    – Catherine
    Commented Feb 27, 2020 at 7:13

2 Answers 2

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While the grind could have been too fine, I suspect what happened is you overfilled the bottom chamber, and the water level was covering the safety valve.

You really don't want the water level to go higher than the red line in the image below.

enter image description here

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    Part two of the answer: From time to time, check that the valve still works (i.e., no crust prevents it from working). You should be able to press it outwards if it still works.
    – DCTLib
    Commented Jul 28, 2016 at 10:47
  • The valve in my pots have no moving parts (i.e., you can't press it outwards) but certainly check there is no crust or other build-up blocking it.
    – Evan
    Commented Aug 1, 2016 at 5:49
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This is certainly caused by the "very fine" grind, which clogged the sieve, letting pressure build up to a dangerous level.

You should use a grind coarser than the one for espresso machines for a moka pot.

Ovefilling with water will result in a burnt taste, as there isn't enough space for vapour pressure to build up quickly. But the over pressure valve would work just fine, venting hot water instead of steam until the water level has dropped.

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