The green patina is pretty typical for any type of copper alloy so you can't really tell much by that. Somewhere in the literature that came with the unit it should mention whether or not it is food grade... beyond that you might just want to drop the mfg and email to ask. I'm not sure if there is any type of treatment you could use to "pickle" the unit... maybe there is a better metallurgist than I out there who could add more info.