Calling all metallugists/chemists

[Matplat]

Morning all,

I recently built myself an immersion chiller from some left over A/C copper coil. Having read about how clean they come up the first time you use them (and subsequent contamination of wort), I was keen to avoid that mishap.

I decided to simply boil the coil in acidic water, to simulate an acidic wort, by adding some hydrochloric acid to 35l of water. As I wasn't aiming for a specific acidity I just poured in the acid 'willy nilly', my guess would be 10-20ml perhaps of 32% HCl, with my town water starting at 8.4ph.

Well my plan worked a treat, copper clean as clean, and my silver soldered joints also look the ducks nuts.

On draining my brewpot I noticed discolouration on my heating element which I initially ignored thinking the sheath had been etched by the acid, and I wasnt too fussed.

After it had dried I realised that there was actually a powdery coating on the element that came off dark on my fingers and that the discoloration looked distinctly copper coloured. I went at it with a scourer which gradually removed all the coppery coloured bits and took the element sheath back to it's original colour, which I'm pretty sure is a nickel alloy of some description.

Considering it is all earthed and there was absolutely no charge on the chiller, Im guessing this was some sort of galvanic corrosion mechanism?

Just wondering if anyone can shed any light on what was occuring, if it was exacerbated by my (likely) overly acidic solution, and if this reaction would be likely to occur at a slower rate during normal use....?

Cheers, Matt

 

[malt and barley blues]

What acid did you use, when I cleaned mine in a similar way I just used the juice of a grapefruit and some vinegar.

 

[MHB]

What you have done is plated out fine copper dust, its a pretty basic galvanic reaction. iron Fe in the element material is probably going into solution and Cu is coming out of solution.
Doing it once probably wont do any harm, make a habit of it and you wont have an element sheath.

If you want to pink the copper before putting it into the kettle, a bit of el-cheapo white vinegar in a bucket of water will do the job, just rinse it off before you put it in the kettle.
Mark

 

[billygoat]

Starsan makes copper nice and shiney as well.

 

[Matplat]

Yeah pretty sure I over did it, but whatever... it worked.

For the record I did try and clean it up with a vinegar soaker scourer first, however the effort:result ratio was not favourable!

The only annoying this is I now need to disassemble the element to make sure it's fully clean. Don't want no metallic flavours in the next brew....

 

[Fraser's BRB]

Based on what I'm reading here, should I have run some water and vinegar through my home made counterflow chiller with copper inner prior to use?

The copper was new and I initially just ran some sanitizer and boiling water through it.

It's had a few brews through it now, so has the damage been done?

 

[manticle]

Copper oxidises. When it oxidises, it goes from bright pink to mottled brown and eventually to green.

Acidic solutions remove that oxidation product, taking it back to shiny pink.

If the chiller (presumably exterior only - interior is just water, yes?)* is oxidised and sits in acidic wort, that corrosion product is removed from the chiller and remains in that acidic solution.

Thus, when brand new, it probably has little corrosion but as it ages, it will be a good idea to clean with a weak acid between brews.

Starsan works, vinegar works, food grade brewing acids work.
Home brand white vinegar is probably cheapest.

*Just reread counterflow as opposed to immersion. Same applies though. Clean between each brew.

 

[Fraser's BRB]

Copper oxidises. When it oxidises, it goes from bright pink to mottled brown and eventually to green.

Acidic solutions remove that oxidation product, taking it back to shiny pink.

If the chiller (presumably exterior only - interior is just water, yes?)* is oxidised and sits in acidic wort, that corrosion product is temoved from the chiller and remains in that acidic solution.

Thus, when brand new, it probably has little corrosion but as it ages, it will be a good idea to clean with a weak acid between brews.

Starsan works, vinegar works, food grade brewing acids work.
Home brand white vinegar is probably cheapest.

*Just reread counterflow as opposed to immersion. Same applies though. Clean between each brew.

 

[Fraser's BRB]

Makes sense, thanks.

 

[Matplat]

FYI, after cleaning it as per my first post, it sat for a day or two, over which time the surface seemed to become tarnished even though it was just sitting in air. Don't know what thats about but whatever....

I decided to clean it again before use, however this time I followed MHBs method of using vinegar and water. That worked just as well with no tarnish!

Stoked as well with the performance of the chiller.... down to 25deg in 20 mins.

 

[GalBrew]

FYI, after cleaning it as per my first post, it sat for a day or two, over which time the surface seemed to become tarnished even though it was just sitting in air. Don't know what thats about but whatever....

That is the copper oxidising. Every time you clean it, it will happen. Leave it long enough and it will turn green. There isn't anything you can do about it, that's the joy of copper I guess.