What’s really happening?

When food sits in the open, tiny living things called bacteria start breaking it down.

Bacteria need three things:

• Water

• Food

• The right conditions

When you bury food in salt, the salt pulls water out of the food.

Without water, bacteria can’t grow properly, so decay slows down.

That’s why the salted sample stayed much better preserved than the control sample.

Ancient Egyptian connection

More than 3,000 years ago, Egyptians used a special salt mixture called natron.

They packed bodies in natron for many weeks to remove water.

After drying, the bodies were wrapped in bandages and placed in tombs.

Many Egyptian mummies have survived thousands of years because they were kept extremely dry.

Where do we still use this today?

People still preserve food by removing water:

• Beef jerky

• Dried fruit

• Salt-cured fish

Different materials, same science.

Big question

If water causes food to spoil, why don’t dried foods last forever?

Try next

• See what happens when bacteria DO have everything they need — warmth, moisture, and food → [The Invisible Colony]

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