[suezo]

Hi, this is my first post here and sorry for my bad english. So, my dad was made a cooling tub for sweet coconut pop ice production. We have a cooling machine with copper pipe to cooling the cooling agent (water+salt). And we use aluminium ice molds and stainless steel made ice mold holder. But after 2 weeks experiment, we decide to disassemble the tub and found the stainless steel holder turn bluish, the copper pipe turn purplish, and rusts on aluminium ice molds. My dad conclude if copper and aluminium in salt water will make a chemical reaction that brings rust to other metal. My question is, is that true? and we got an advice to change the salt water to Ethylene glycol, is that will solve the problem? Thank you in advance.

[Arkcon]

Yes, what you've encountered is galvanic corrosion, and the Wikipedia page (in English) has a photo for you to compare:  http://en.wikipedia.org/wiki/Galvanic_corrosion  See how the explanation works in your language, you may understand terms better.  If the corrosion isn't so bad, you might want to leave things as they are, and simply claen more often, to avoid damage. 

Using ethylene glycol might help, but a better choice would be antifreeze, which has other additives to further prevent corrosion.  But be careful, if there's a chance that you could contaminate product with the coolant, you run the risk of seriously injuring people, and end up another statistic -- a company that didn't think ahead, hurt people, and needed a serious government smack down after the fact.

You could use food grade proplyene glycol, but it is likely expensive.

[billnotgatez]

I am not quite sure of your set up but
Could you use something that is not as corrosive as salt water and not have the issues that antifreeze which have been suggested in previous posts.
For instance
sugar water (sugar concentration greater than pops)
or
Glycerol /glycerine
either could also have sufficient ethanol (Vodka) added to prevent microbe activity