Blue water from wort chiller in PBW

[brewshki]

The other week I left my worry chiller soaking in PBW and then got busy and forgot about it. I came back after a few days and emptied the bucket. Well, the PBW solution was completely blue. The wort chiller was not. I washed it and rinsed out the bucket. I know the reaction between the chiller and the PBW caused the discoloration, but is my wort chiller still safe to use. I have also left it in starsan before have learned not to do that as well. Can anyone explain what goes wrong with that? Thanks!

Also, I have since used that chiller in a batch. I haven't had any of the beer yet as it is conditioning, but is it safe to drink?

 

[brewshki]

It was an immersion chiller.

 

[k-moe]

The copper reacted with the PBW and made a verdigris solution (technically it's more like an Egyptian Blue solution since alkali was used). As long as the surface of the copper is not blue/green you can continue using it (basically, rinse any remaining verdigris from the surface of the chiller). In the future you should refrain from soaking your chiller in PBW; eventually it will become too thin to use.

If you have any interest, you are on the cusp of beginning pigment-making as a hobby.

 

[brewshki]

The copper reacted with the PBW and made a verdigris solution. As long as the surface of the copper is not blue/green you can continue using it (basically, rinse any remaining verdigris from the surface of the chiller). In the future you should refrain from soaking your chiller; eventually all that will be left of it is a verdigris solution.

Will do! Thanks very much! I definitely scrubbed any of the few green parts off.

 

[brewshki]

View attachment ImageUploadedByHome Brew1456680273.066455.jpg

 

[Thi_Hund]

Hi, I am a chemical engineer and home brewer, and I have a theory about this.

PBW is safe to use with copper and aluminum, according to the manufacturer sheet.

However, several people reported blue solutions after a long contact time with the cleaning product. I cannot give you a 100% confirmation of what happened since only a laboratory analysis can provide that accuracy level. But my theory is: Copper reacts with the sodium carbonate (Na2CO3) in the PBW and water to produce Basic copper carbonate (CuCO3), more properly called copper (II) carbonate hydroxide [Cu2CO3(OH)2]. This compound is greenish/blue.

Other reactions can occur too. Copper carbonate can also react with water under normal conditions to form azurite [Cu3(CO3)2(OH)2], which has a more intense blue color.

These reactions happen very frequently with copper metals. When they happen, people often get the idea to use vinegar to "neutralize" the alkaline reactions, but this can form copper (II) acetate, which is also blue. That's why using peracetic acid as a sanitiser in copper chillers also renders the same color to the solution. Other posts on Homebrew Talk can provide with some pictures of it.

I would say that PBW is safe to use with copper, but you should keep a short period of time to avoid corrosion and pitting. I like to rinse my chiller with tap water to clean any chemical residue after use.

Additionally, if you use citric acid to passivate your metals, you should know that citric acid will form copper citrate, which is also blue. This happened to me recently, which motivated me to look it up for possible reactions.

Cheers.