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moka pots - lethal damage?

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  • moka pots - lethal damage?

    I have decided to put back into service two moka pots Bialetti "Cuor di Moka" (Heart of Moka), a special model which has a valve that stops the flow after a certain quantity of water has gone through the filter, to prevent the bitter taste of over extraction.

    They had been sitting on a shelf for a couple of years at least, so I've decided to give them a good clean and, as there was heavy coffee deposits in areas of the pots which are not accessible, I've had the "brilliant" idea of soaking the top part of the pots in a solution of hot water and coffee machine cleaner. I received a long phone call shortly after that and therefore left the pots to soak for much longer than I wanted to, and at my return the shiny appearance had been replaced by a dark gray slimy patina. I now realised that probably what I thought was a polished finish was in fact clear hard anodising and the the cleaner must have removed it exposing bare aluminium which has oxidised creating the gray patina. I can remove the patina by rubbing the surface in some areas, but not all areas are accessible, especially those were the flow of coffee runs.

    So the question is: does anyone know if, beyond the cosmetic change, the damage to the pots finish is of such an extent that they can no longer be used, i.e. the pots are no longer food safe? Is there anything I can do?

  • #2
    Yeah, Sodium Percarbonate (the main constituent of Cafetto, etc) is not compatible with anything manufactured from Aluminium. Here's a brief extract from a science forum describing why, for it and other similarly basic compounds...


    "Boiling aqueous sodium bicarbonate (a very common ingredient to cleaning dishes as it does not leave spots) unfortunately breaks down the NaHCO3 forming functionally sodium hydroxide with the release of carbon dioxide gas. The reaction of aluminum and the created sodium hydroxide is very exothermic resulting the dissolution of the aluminum with the formation of sodium aluminate and production of hydrogen gas.

    To demonstrate what I'm talking about, dissolve some baking soda ( which is sodium bicarbonate) in water and place in an open jar. And some flakes of aluminum foil and place in a microwave for 30 seconds. The aluminum foil will be very rapidly attacked, which is obviously not what you don't want to happen in your dishwasher with aluminum products.

    Avoid sodium percarbonate products, as per a thread I once did, it is actively not Na2CO3/H2O2 due to additives to boost bleaching ability by creating some very dangerous products (so believe the large print multi-language warning labels!).

    Bleach is also very alkaline, so I would avoid using it as well, and definitely do not mix it with baking soda as that produces hypochlorous acid (HOCl), which while great for disinfecting, it breaks down to HCl, which can further react with the HOCl to generate chlorine gas (and water), obviously something to be avoided!

    Note, the combination of heat and surfactants (as found in soap/cleaning products) do a great job at killing bugs (by tearing them apart), so I really don't think you have to worry about that so much. In my opinion, focus on not corroding your disk washer and avoid using products not intended for use in your machine."


    • #3
      Cheers, I wish I’d checked that before assuming that the cleaner would be suitable for any kind of coffee maker.

      I’ll have to find out if the sodium aluminate, which I assume is the gray slime I’ve found on the pot surface, is toxic; I’ve rubbed off almost all of it but I’m sure there will be some traces left somewhere.....