I am in the process of building a fermentation temperature controller (in the same spirit as the grainfather glycol chiller), the process is mostly done and I am testing the system with water.

The heat exchange is made through a hand-bent copper tubing plunged in the fermentation vessel; the problem is, after a day or two, the water inside the vessel takes a light yellow tint and there is a rust spot at the bottom of the vessel (the chiller touches it).

So my questions are, will this affect the beer? Is there a way to prevent it? I am thinking the yeast will eat the oxygen, preventing oxidation but will it be enough? worst case scenario I'll buy an inox chiller but its a bit against the DIY spirit :)

Thank you for your time!

  • You are not fermenting yet, just using your coil in a vessel with water to test your system? Because you say "the water in the vessel", not "wort in the vessel".
    – chthon
    Aug 23, 2019 at 10:33
  • Yes as I said I'm testing with water first to check the efficiency of the system, that's why I'm wondering if this issue won't go away when I put wort.
    – SeekDaSky
    Aug 23, 2019 at 11:52
  • There must be something else, but maybe your water is has a high pH. When I search for dissolving copper in water, and copper water reactions, I only find that water should not have an effect on copper. For acids (wort is acidic), only oxidising acids dissolve copper, but I can't find any proof that wort is an oxidising acid.
    – chthon
    Aug 23, 2019 at 17:24
  • last time I checked the water I use was around 8pH so it can't be it, maybe the copper just have a thick layer of dirt from being stored in some warehouse, I'll try to clean it more thoroughly, maybe with a light abrasive?
    – SeekDaSky
    Aug 23, 2019 at 17:28

2 Answers 2


First this: How to Brew: Brewing Metallurgy

Apparently, there should be no problem in using a copper chiller in your fermenting beer. Make sure there is no oxidation before you use your cooler.


How clean is your copper coil? If it were me, I'd be going straight for stainless, to be honest. If you want to go the DIY copper route, keep the copper outside the fermenter by wrapping it around the outside, a sort of DIY jacket, if you will.

  • 1
    I cleaned the coil before testing (though not as much as I would with a real batch of beer). Stainless probably is the way to go but I think I'll try a batch with the copper one before, for science. And wrapping the copper around the vessel is not nearly as efficient.
    – SeekDaSky
    Aug 23, 2019 at 6:50
  • Not nearly as efficient, but a damn sight easier to clean. Add some insulation, and you'd be fine.
    – Frazbro
    Aug 26, 2019 at 1:16

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