Why honey never spoils

0:00 Archaeologists have opened Egyptian tombs and

0:02 found honey that was still perfectly edible

0:05 after three thousand years.

0:06 Honey survives because it is a hostile place

0:10 to live.

0:10 It holds very little free water,

0:13 so any bacterium landing in it is drawn dry

0:16 by osmosis.

0:17 It is also acidic, around pH four,

0:20 and bees add an enzyme that slowly releases

0:24 hydrogen peroxide.

0:25 Nothing much can grow in that combination.

0:28 The catch is the water part:

0:30 honey pulls moisture from the air,

0:33 so a jar left open long enough can dilute

0:36 itself at the surface and finally ferment.

0:39 Sealed, though,

0:40 it is less a food than a very slow chemistry

0:43 experiment.