Microorganisms require certain conditions like food, water, temperature, and pH levels to survive and reproduce. Food can be preserved by destroying microorganisms through methods like heating, drying, salting, pickling, fermenting, pasteurizing, canning, and freezing. These techniques either kill the microbes or prevent them from growing and spoiling the food.

2. Microorganisms, like other living organism,
require food, water, oxygen, and suitable
temperature for growth and reproduction.
In addition, microorganisms can only survive in
conditions with optimum pH and solute
concentrations.
Food can be preserved by destroying the
microorganisms present in the food by stopping
the activities of these microrganisms.

3.  Prevent food spoilage.
 Heating food at higher temperatures can kill
microorganisms and denature the enzymes that
can cause the breakdown of food.

4.  Treating food with salt or sugar causes the
microorganisms to lose water due to osmosis.
 Pickling food with vinegar reduces the pH and
prevents microorganisms from growing.

5.  Fruit juices and other food substances can be
fermented by adding yeast.
 Fermentation of fruit juices produces ethanol
which at high concentrations prevents the juices
from becoming spoiled.
 The ethanol produces has great commercial
value.

6.  Fish, meat and fruits can be dried to preserve
them.
 Drying under the hot sun removes the water from
food, and this prevents the microorganisms
from growing.
 The ultraviolet rays of the sun also kill bacteria
and many other microorganisms.

7.  To destroy bacteria which cause diseases such as
those tuberculosis and typhoid.
 This method retains the natural flavour of milk.
 Milk is heated to 63°C for 30 minutes or to 72°C
for 15 seconds followed by rapid cooling to
below 10°C.

8.  Uses heat sterilisation to kill microorganisms and
their spores.
 The food is packed in cans and steamed at high
temperatures and pressure to drive the out air.
 The cans containing food are then sealed while
the food is being cooled.
 The vacuum created within the cans prevents the
growth of microorganisms.

9.  Food stored at temperatures below 0°C can
remain fresh for a long period of time.
 The extremely low temperatures prevent the
growth of microorganisms or germination of
spores.