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  • Milk drawn into boiler

    How easy or hard is it to get milk sucked up into the boiler if you forget to purge the steam wand before and after steaming milk? It worries me.

  • #2
    I can't see how this would be possible with positive pressure in the boiler, can a boiler develop a vacuum?

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    • #3
      Wouldn't negative pressure develop as the boiler cools? And, if there happened to be a bit of milk inside the steam wand, isn't it possible it could be drawn into the boiler as it cools after shutdown?

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      • #4
        You've got me worried now. Where are the engineers and physicists when you need them?

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        • #5
          Very unlikely, unless your anti-vac valve is stuck, the machine cools down and you leave the wand sitting in a jug of milk all day, then open the steam valve (yes, I've seen it done).

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          • #6
            Anti-vac valve, is that what is sometimes referred to as a downstream valve? Also, if this valve does stick, wouldn't the boiler implode, since a boiler is only designed to withstand positive internal pressure?

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            • #7
              Originally posted by Bernsbrew View Post
              Anti-vac valve, is that what is sometimes referred to as a downstream valve? Also, if this valve does stick, wouldn't the boiler implode, since a boiler is only designed to withstand positive internal pressure?

              Boilers do implode every once in a while. Rapid cooling without pressure equalization (i.e. opening up the steam valve) has lead to the loss of more than a few boilers over the years. Although, this does not seem to be as much of an issue with newer machines. Superior boiler design perhaps?

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              • #8
                I would imagine not very difficult once the anti-vac valve is stuck. I say this as I bought an old commercial HX which had milk taint in the boiler. I had seen the owner use it and leaving wand in jug of milk etc was not what he did, however purging wasn't done either. Once home and and the machine properly assessed, the anti-vac valve was stuck and the steam coming out of the boiler was foul - very 'off-milk' taint to it which made any steamed milk undrinkable.

                I am confident that this machine became tainted due to anti-vac being stuck for some time and the wand not being purged so all it takes is someone to open the steam valve when cold, or the steam valve not sealing properly and that milk makes its way back to the boiler.

                I not only purge the wand religiously, but I also listen as my machine comes to boil to make sure that anti-vac valve is still working.

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                • #9
                  Would be more related to machine malfunction than user error on a newer machine.

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                  • #10
                    There are fairly regular threads where people have milk taint in their boilers. I always make sure that I clean and purge the steam wand whenever I make a milk drink, it's just good hygiene

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                    • #11
                      Do you guys steam a jug of water after each use? I was told to do this. It only takes about 15 seconds and you see all the milk particles in the water even after purging. If anyone didn't steam the jug of water that would become stuck inside the steam wand and eventually go off..

                      This would also avoid someone leaving the wand in a jug of milk etc. It's just a habbit I now obtain and I guess it just works.

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                      • #12
                        Originally posted by neofelis View Post
                        Do you guys steam a jug of water after each use? I was told to do this. It only takes about 15 seconds and you see all the milk particles in the water even after purging. If anyone didn't steam the jug of water that would become stuck inside the steam wand and eventually go off..

                        This would also avoid someone leaving the wand in a jug of milk etc. It's just a habbit I now obtain and I guess it just works.
                        Steaming a jug of water is more about cleaning the outside of the wand. As for any milk inside the wand, that would have been forced out pretty quickly with the first few blasts of steam.

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