What’s really happening?

When food is left in the open, microorganisms such as bacteria and fungi can begin breaking it down.

These microorganisms grow best when they have enough water, nutrients and suitable conditions.

Salt helps preserve food because it draws water out of the food and makes less water available for microorganisms to use.

With less available water, bacteria and fungi struggle to grow and reproduce, so decay slows down.

That’s why your natron-treated sample may have become drier and changed more slowly than the control.

Ancient Egyptian connection

More than 3,000 years ago, ancient Egyptian embalmers used a naturally occurring mineral mixture called natron.

They packed bodies in natron for many days to draw out moisture and dry the tissues.

Once dried, the body could be wrapped and prepared for burial.

Removing water was one of the key reasons mummified bodies could resist decay for such extraordinary lengths of time.

Where do we still use this today?

Humans still preserve foods by reducing the amount of water available to microorganisms.

You can see the same idea in:

• beef jerky

• dried fruit

• salt-cured fish

• dried herbs

Different materials — same preservation principle.

Big question

If removing water slows down decay…

why don’t dried foods last forever?

Try next

• Find out what happens when microorganisms have plenty of moisture and food → The Invisible Colony

• Explore another chemical change that permanently alters a material → [Hidden Messages]