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  • Copper / Brass versus Stainless Steel

    Copper has the highest heat conductivity with Brass an alloy of copper and zinc next.

    Stainless Steel has about 1/6 the thermal conductivity but has about 20% greater heat capacity.

    This is why you can have saucepans with SS handles and they don't get hot. If you tried this with brass or copper, it would be friggin' hilarious watching Master Chef play with their new pots and pans.

    Of course, SS is inert chemically and is much harder. This is why most copper or brass in your machine needs lashings of nice Chrome over it to make wear surfaces much harder. It also makes it more chemically inert and hence much less likely to impart flavours to your brew that are unwanted.

    I have an E61 machine. No one is going to ever design a SS E61 head...period. The whole idea is that the whole head heats up quickly and evenly something SS isn't good at.

    Contentious areas are things such as boilers and portafilters. A boiler I can't see any advantage in brass but I can see some downside as it is chemically more reactive. A boiler just holds water. I suppose one advantage is brass is easier to work, drill etc.

    Portafilters made of SS are popular. I was looking at my new one and realizing differences right away. A SS one the handle won't get hot whereas the entire head will get hot on a brass/chrome one. I run water through the portafilter first before a shot which should negate differences there but the brass one will definitely be at more or less a uniform temperature ALWAYS whereas the SS one won't be. The only possible difference would be SS absorbing heat from the shots. The contact time is only of the order of a few seconds in the portafilter and so the reduced heat conductance of SS would mean less heat would be adsorbed although the SS is likely to be cooler than with an all Brass/Copper portafilter.

    My guess is it makes little or no difference but certainly with portafilters it makes it extra important, even essential that you make sure your SS portafilter is properly pre-warmed with water before using it for a shot. The benefit of SS is cosmetic mainly but no doubt high chrome SS will last pretty well forever and no chance of plating wearing off.

  • #2
    I recall reading somewhere about stainless boilers not being ideal as the temp/pressure can lead to pitting?

    I find SS is very easy to wipe clean, even compared to chromed brass (talking PFs).

    Good point about pre warming the PF properly. I guess thats why some appliance machines use a plastic insert inside the PF, reduces the effect if the PF is not fully warmed. I now exclusively use a naked PF so the warming is less of an issue as the basket heats up quick due to very low mass and no water actually touches the PF.

    When I made a naked PF, I was amazed that the plating didnt start to peel off at the cut line.

    Cheers

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    • #3
      Originally posted by artman View Post
      I recall reading somewhere about stainless boilers not being ideal as the temp/pressure can lead to pitting?

      I find SS is very easy to wipe clean, even compared to chromed brass (talking PFs).

      Good point about pre warming the PF properly. I guess thats why some appliance machines use a plastic insert inside the PF, reduces the effect if the PF is not fully warmed. I now exclusively use a naked PF so the warming is less of an issue as the basket heats up quick due to very low mass and no water actually touches the PF.

      When I made a naked PF, I was amazed that the plating didnt start to peel off at the cut line.

      Cheers
      The EU, reportedly is legislating SS for boilers. SS is used in the Dairy industry for a wide range of applications including areas where there is heat. Believe me, provided the correct grade of stainless is used for the application, you shouldn't get corrosion issues except in exceptional situations. Milk products are pretty bad too for production of acids and the like.

      The chrome on portafilters will last for decades, if it is a good coating of chrome although this would depend on manufacturing. The Bezzera portafilters are 20 years old and the chrome hasn't worn off anywhere I can see.

      Edit: The La Marzocco boilers were probably the first to go SS in the seventies, long time ago.

      Comment


      • #4
        Originally posted by wattgn View Post
        Edit: The La Marzocco boilers were probably the first to go SS in the seventies, long time ago.
        True and caused a lot of people a lot of trouble due to trashed boilers after a very short time...
        Very important to make sure your water filtering is specifically identified as suitable for removing all chlorine compounds.

        Mal.

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        • #5
          Chlorine could be an issue if you don't filter especially in a commercial environment with boilers running a long time but it would be careless not to filter. It would take a long time though to cause any real issues and high chlorine in the water.

          If LM have been using SS boilers for nearly half a century, one would presume these issues are sorted and it may be dependent on SS grade used.

          All boilers are going to SS anyway, so maybe a mute point.

          Carbon filters remove reactive products like free chlorine and associated compounds, chloride such as salt isn't reactive but isn't an issue.

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          • #6
            Originally posted by wattgn View Post
            All boilers are going to SS anyway, so maybe a mute point.
            Maybe 'moot'...

            Not for me they won't be....
            If I ever decide to head to a different espresso machine in the future, it will NOT have a s/s boiler. Just don't need the hassle...

            Mal.

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            • #7
              Then avoid La Cimbali, LM, Wega, La Pavoni, ECM others. They obviously have no idea...amateurs...

              In the Dairy and Wine Industry just about anything contacting product is 316 Stainless Steel which is high nickel, high chrome alloy and very chemically resistant.

              In some ways, brass is anomalous with espresso machines but it is there for reasons of conduction.

              A boiler with a bridge to the group head such as the Bezzera BZ40P I have, requires a brass boiler for conduction. It won't work otherwise.

              Most E61 machines will have Stainless Steel boilers as they don't need the brass conductivity as the head is warmed by thermosiphon.

              I know there is some concern about drinking water kept in contact with brass at temperature which is influencing the EU to possibly move on this but I'm not really sure how far it all goes. Brass is certainly not as inert as Stainless and depending on pH you could get thinning of boilers and this goes into the steam and some into the espresso also.

              I had my next door neighbour out today (a plumber). I nicked a copper water pipe with pruning shears while investigating the reticulation. I commented it was really soft and he said, 'well depending on the water acidity, it can result in thinning of the Copper and it looks like your pipe maybe has thinned out a bit". He welded the piper for me. On a Sunday...wow.

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              • #8
                Boilers (non SS) in espresso machines are generally close on pure copper.

                Comment


                • #9
                  Originally posted by Talk_Coffee View Post
                  Boilers (non SS) in espresso machines are generally close on pure copper.
                  Brass or Copper, the chemistry would be similar. Copper is softer and heavier and more conductive.

                  Comment


                  • #10
                    In the presence of high temps, higher than desired TDH and chloramines, copper every day. It is an issue in many parts of Australia.

                    Wine and milk is not espresso machine boiler.

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                    • #11
                      Originally posted by Talk_Coffee View Post
                      In the presence of high temps, higher than desired TDH and chloramines, copper every day. It is an issue in many parts of Australia.

                      Wine and milk is not espresso machine boiler.
                      Many leading companies use both Copper and Stainless boilers so I doubt either will cause issues except in unusual circumstances. Both stainless and copper have been used for decades in espresso machine boilers and will last for decades.

                      Stainless steel is used for food processing as there is ZERO risk of imparting flavours to foods and it allows the use of powerful alkaline and acidic chemicals for cleaning equipment and machinery. Copper does definitely leach into water over time though depending on pH and other factors and it is this chemical reactivity that means it isn't favoured even in equipment such as heat exchangers. Copper can also cause other issues such as visual defects due to the coloured copper salts finding it's way into foods as coloured particles.

                      Coffee is different though as there is no scrubbing or cleaning involved internally unlike food contact surfaces, so Copper and brass is an option.

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                      • #12
                        Copper and brass with high silver brazing alloy welds are extremely resilient. Fabricated and welded stainless boilers can degrade over time due to repeated heating and cooling cycles, which embrittles the material, particularly in big boilers.

                        That's why I don't recommend people turn off their commercial machines with SS boilers over night, even if it is the right thing to do to conserve energy.

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                        • #13
                          Originally posted by coffee_machinist View Post
                          Copper and brass with high silver brazing alloy welds are extremely resilient. Fabricated and welded stainless boilers can degrade over time due to repeated heating and cooling cycles, which embrittles the material, particularly in big boilers.

                          That's why I don't recommend people turn off their commercial machines with SS boilers over night, even if it is the right thing to do to conserve energy.
                          Well, we should be seeing quite a few boiler failures then with SS boilers is all I can say but call me skeptical about that....

                          I'd also be pissed off if I paid 8k for a LM machine see the boiler fail prematurely.

                          This is why I am skeptical. If companies with massive investment and respect were getting a lot of issues with a component in their system they would simply change back. Even Rocket Express are using Copper boilers but with nickel plating to avoid copper corrosion issues.

                          I see it as even money either way in that no one is going to be disadvantaged whatever material they use.

                          It doesn't pass the logic test with me.

                          Mind you it makes it an interesting thread with lots of potential...

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                          • #14
                            You're really preaching to people who, either by virtue of their professional qualifications or significant research from long ago, already understand the pros and cons of opting for one metal or another in an espresso machine boiler. I choose copper over s/s because that's what my research, over some considerable time, tells me has fewer cons than s/s.

                            Everyone can choose what best suits them after doing their due diligence research from reputable sources. You're never going to sell me on s/s boilers over pure copper...

                            Don't forget the marketing push by various companies claiming the so-called benefits of s/s over copper too - Has nothing to do with absolute benefits. Believe what you will...

                            Mal.

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                            • #15
                              Believe whatever you want sir. I'm just the guy that swaps out the boilers when they fail. Note I should have said long periods, usually 10+ years of heat cycling. All materials have issues, nothing is perfect and espresso machine design is a continual compromise.

                              Kees van der Westen is my go to when I want to follow an example of best practise - copper steam boilers and heat exchangers (big temperature cycles), copper plumbing, brass fittings and brew boilers/groups fabricated in 316L stainless.

                              I have replaced the brew boiler in my original Mistral (90's Marzocco boilers, these were built on Linea parts) as the S/S tube was flogged from heat cycling, it sweated. Quite common for this era now at this age.

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