[TheForge] Food grade metal

[Bruce .]

Some clarifications upon what James is telling us:

Pure metallic copper will not be dissolved by most common foods.  (Citric
acid may have a chance of doing so.)  But copper will easily air-oxidize
(tarnish), especially when wet, and the resultant copper salts WILL
dissolve even in dilute acid.  That's why a copper bowl should be cleaned
with vinegar and salt before use with anything but pure water.  Copper is a
poison, no ifs, ands, or buts about it.  Trace copper might be necessary in
the diet -- but "trace" means VERY VERY LITTLE.

Aluminum always has a protective oxide layer, but that layer can be broken
down fairly easily by alkali (lye, washing soda, etc.), and somewhat less
easily by acid.  I've seen an aluminum pan perforated by tomato sauce --
but only after it was stored a while in the pan (in the fridge).  I know of
no reliable information implicating aluminum as toxic.

Iron, of course, rusts easily and shouldn't be used to store foods.  Cast
iron is fine for cooking, however, because it is seasoned first.  Be aware
that excess iron in the diet IS toxic, but human tolerance is pretty high.


On Mon, Sep 9, 2013 at 6:03 PM, James Binnion <jbin at well.com> wrote:

> 304 or 18-8 stainless are considered food safe because nothing you are
> going to eat can typically dissolve the chrome oxide surface passivation
> layer. Copper, aluminum, steel or iron all can be dissolved by acids in
> foods like tomatoes or citrus. The truly paranoid don't want to ingest
> those metal compounds. So for storage appropriate grades of stainless are
> the only common alloy that is not going to be easily dissolved by some
> foods. Of course gold and platinum would be food safe as would titanium.
>
> James Binnion
> jbin at well.com
>
>
>
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-- 
Bruce
NJ