Food preservation lengthens the life of foods.

Freezing: vegetables e.g. peas

Dehydrating: milk e.g. powdered milk

Freezing preserves the vegetables as bacteria cannot survive at such low temperatures (their enzymes aren’t able to function). Also all the water in peas is turned to solid ice and bacteria need water in order to survive.

Dehydrating preserves powdered milk as the bacteria have no water. All living things need water as a medium for their reactions.

The main cause of famine is crop failure in third world countries caused by droughts and pests.