Nitrogen
What it does
Modified-atmosphere packaging; keeps food fresh.
How it's made
Purified from air.
Nitrogen is an inert gas used very widely in food packaging to replace oxygen and protect foods from going stale or rancid — it is the gas that fills bags of crisps and many other packs — and also to pressurise and dispense products and to freeze foods rapidly as a liquid.
It is separated from the air, which is about 78% nitrogen. Air is compressed, cooled until it liquefies, and then fractionally distilled: as the liquid air is gradually warmed, nitrogen (which boils at a lower temperature than oxygen) comes off first and is collected. Nitrogen can also be separated from air by membrane or adsorption technologies.
The purified nitrogen is compressed or liquefied for use. Because it is inert and makes up most of the air we breathe, it is completely harmless in this role; by pushing oxygen out of a package it dramatically slows the oxidation and mould growth that would otherwise spoil the food.
Possible reactions
Inert and safe.