eli5 how does an oxygen absorber inside a food packet or any other packet work? Does it have any expiration date like it will stop absorbing after certain saturation?

Question

What do the small crystals inside it exactly do?

In: Chemistry

Answer 1

The easiest way to consume oxygen is to burn something which consumes both the oxygen and the fuel you’re burning. But that gives us three problems to solve:

1) Burning stuffy creates messy debris we wouldn’t want in our food, so let’s put it in a packet.

2) The next problem is that burning something usually releases not only heat, but enough heat to create fire: so let’s use something that burns insanely slowly, so slowly it barely gets warm at all and makes no fire.

3) Even in a packet, most things we burn (or the ashes they make) wouldn’t past food safety standards, so we need something that’s “law-suit safe” level harmless, something that wouldn’t make people sick.

What’s the answer? Iron Filings! (that’s a tad bit oversimplified).

But basically just iron dust. Iron is both a generally harmless mineral for people AND it likes to burn with oxygen to create rust, in other words rusting Iron is the “watching paint dry” version of a bonfire.

So that’s what’s in those little packets, a special form of iron dust that left alone is just.. iron dust. But expose it to oxygen and the iron will slowly absorb the oxygen, becoming an “iron oxide”, i.e. rust.

They pretty much only expire because of lawsuit and warranty stuff. You can imagine if they didn’t have an expiration and a there were a class action lawsuit against “Lardo Brand” meat-chips or whatever, Lardo could try blaming the packet manufacturer, et. etc.