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Avoiding limescale in espresso machines-remove Calcium or add phosphates?

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  • Avoiding limescale in espresso machines-remove Calcium or add phosphates?

    I am trying to do the best for my espresso machines. Last week I had a machine that kept heating after the pressurstat was needed to shut power to the element. Luckily I was there to see it and shut the machine down.
    The fault was traced to limescale between the pressurstat and its joining pipe...the one that connects into the base of the sightglass. This was causing a blockage, not allowing the pressurstat to do its job properly.

    I run a twin undercounter filter setup (for drinking water) that feeds into a separate filter that is filled with resin that pulls Calcium ions out of the water as it passes through. I have used this type of system for many years. My town water is around 60ppm total hardness and is less than or equal to 10ppm of total hardness after it passes through the softening filter (which goes into an espresso machine). This resin can be regenerated with a salt soak and flush.

    Today I have sent and received a few emails and spoken to a few people in the water filtration industry and am now in a bit of a dilemma. I can either-
    *replace the resin in the softening cartridge with new or perhaps a different type of resin.or
    *use a totally different type of filter in the cartridge. I was told that this newer type of filter is being used in cafes around Newcastle that have town water less than 150ppm total hardness.

    From the seller's website-
    Description

    1025Phos/GAC Triple Action Food Service Water Filter for 10″ Filter Housings.


    The 1025Phos/GAC is an Activated Carbon / Polyphosphate Food Service Cartridge Designed for the food service industry.

    Protects coffee machines, ice machines, steam ovens, boilers, refrigerators and other water-consuming appliances from scale build-up. Can be used in both residential and busy commercial operating environments.


    Also improves the taste and odour of beverages significantly, which makes it ideal for appliances which generate drinking water, ice, coffee, slushees, and other drinks.


    This is an Australian-made High Performance Filter manufactured by 3M™. Produced using high-quality components and manufacturing techniques, for which 3M™ is renowned.
    This type of filter allows Calcium to pass through but stops the Calcium particles from sticking to internal parts of the espresso machine.



    Does anyone in the know have any thoughts on which filter would be best suited to an espresso machine application?



  • #2
    The polyphosphate cartridge doesn't really* allow the calcium ions through. They will react with the phosphate to form calcium phosphate which is fabulously insoluble (this is a good thing since your teeth are made of a different form of calcium phosphate).

    Just like your teeth, if you expose the calcium phosphate to something very acidic it will pull some of the calcium out. That won't happen in a coffee machine so this should work very well.

    Since it doesn't replace the calcium with sodium the way the standard exchange resins do you may notice a change in flavour: low levels of sodium ions generally act as a flavour enhancer.

    Interestingly (to me, anyway) the same reaction is partly why beer is so sensitive to the water from which it is made. Barley, like most seeds, has a very high level of phosphates. The calcium in the mash water reacts with the phosphates and drops them out allowing the counter ions of the calcium to reduce the pH.


    *Techically the calcium ions are still present but they are unavailable because they are tightly bound to the phosphate.
    Last edited by Lyrebird; 15 August 2022, 08:25 PM.

    Comment


    • #3
      Thanks for this information, Lyrebird!
      One of the water filter guys told me that this polyphosphate filter would (over time) deplete Calcium deposits out of a scaled machine. This sounds too good to be true. What are your thoughts on this?

      Comment


      • Lyrebird
        Lyrebird commented
        Editing a comment
        I can see two scenarios;

        Firstly, pulling the calcium out of the water could drop its pH : as an example if the calcium ions are present with chloride ions* and you take out the calcium ions with polyphosphate which is balanced with hydrogen ions you end up with the chloride ions and the hydrogen ions so you have hydrochloric acid solution.

        The lower pH should indeed remove scale, albeit slowly.

        The other case is where the polyphosphate is present as a salt such as sodium polyphosphate (I hadn't considered this in my frst reply). In that case you would end up with sodium chloride solution. If you soak scale in a sodium chloride solution for long enough some of the divalent cations in the scale will exchange with sodium. Since the chlorides of alkaline earths and almost all salts of sodium are soluble, this is a net increase in solubility.



        * the total sum of ions in solution has to add up to zero net charge, since the reason they are ions is that they stole electrons off each other. This means that cations like calcium, which have lost electrons and are thus positively* charged must have countervaling anions like chloride, which gain electrons and are thus negatively charged.

        In this case you need twice as many chloride ions as calcium ions since chloride has a single electron added while a calcium ion has two electrons missing.

        FWIW polyphosphate is effectively condensed phosphoric acid so the hydrogen ions come from there rather than appearing by magic.



        * Damn you Ben Franklin.
        Last edited by Lyrebird; 15 August 2022, 09:41 PM.

      • Lyrebird
        Lyrebird commented
        Editing a comment
        The above is slightly inaccurate as I forgot to account for the fact that phosphoric acid will only partially dissociate at water pH (it's technically a weak acid). This biases towards the first answer.

    • #4
      I will contact 3M tomorrow and ask in what form the polyphosphate content is present in the cartridge that they manufacture. It is apparently made in good ol' Oz.
      It would be interesting to know what the pH change will be of the water that comes through this filter.

      Comment


      • tompoland
        tompoland commented
        Editing a comment
        And interesting to see if there is a change in flavor with the new water.

        Following with interest because the new home needs a water filter system installed. Currently using a Brita Walter filter jug with cartridges as a short term way of minimising scale build up.

      • Lyrebird
        Lyrebird commented
        Editing a comment
        I thought of a third scenario, there are probably others. The third is a little complex to explain (it involves the way that exhange resin beds work) but it should also act to remove scale.

    • #5
      I didn't have much luck with finding anything out from 3M.
      Another water filter company mentions that their Polyphosphate crystals (that they sell as raw crystals) degrade and the housing that contains them should be 'topped up' each month. Not sure if this concept bothers me...I have enough foreign thingies in my body already.

      Does anyone know what type of resin Brita uses in their 'finest' cartridges?
      I might just go with a mixed bed resin and change it annually.

      Comment


      • Lyrebird
        Lyrebird commented
        Editing a comment
        Sodium phosphate is the main ingredient in many toothpastes so this doesn't represent anything to which you aren't already exposed.

    • #6
      Thanks for your reply, Lyrebird.
      The person who fielded my call at 3M and another water filter guy were unable to supply me with a technical data sheet on their polyphosphate filters and couldn't tell me what the form of phosphates are used, so I don't know that it is sodium phosphate or some other form.

      I am leaning to fill my 10" cartridge with the "most suitable for espresso machines" resin that I can find.

      The existing resin in my softening filter is advertised as- "Calcium Targeting Limescale Resin Hard Water Softening Car Wash Filter T-Resin".It is the type that can be regenerated with a salt and water soak and then rinse.

      Do you know of a more suitable resin that would be suitable for both copper and stainless boilers?

      Comment


      • Lyrebird
        Lyrebird commented
        Editing a comment
        No, sorry, I don't. It's a long time since I worked in this area but you are describing a typical mixed bed resin which is what is used in single stage cartridges.
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