> On the cool side, some kind of heat sink will extend into the jug and
> will be in direct contact with the fluid which it will cool. My question
> is: what type of heat sink is safe for this purpose?
>
Aluminum soda cans are coated inside with plastic.
I don't know if it's a safety issue or (more likely) a taste issue.

While copper sounds interesting, Solder does not.
I still use lead solder for my electronics, but we are forbidden
here for using it on potable (drinkable) water lines.
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