Conditions for bacterial growth
There are five main conditions for bacterial
growth
• Temperature
• Moisture
• Time
• Ph level
• Oxygen
Temperature
• Bacteria grow best at 37C
which is body temperature.
They reproduce quickly
between 3C and 63C which
is the danger zone. Cook
chilled food should be
stored at 0C to 3C.
• To control temperature food
should be
• Cooled to below 3C
• Heated to above 63C
Key temperatures
• Above 121C all bacteria and
spores are killed
• 72C temperature of
reheated food
• 63C Food should be heated
above this temperature
• 3-63C danger zone for
bacterial growth
• -18C temperature of freezer
• -22 temperature to freeze
food.
Moisture
• Bacteria like moist conditions.
Many foods contain liquid
• Controls for moisture
• Dehydration-removing the
water like in dried milk
• High sugar content- makes less
water available like in jam
• Salt removes water by
osmosis like in bacon.
• Freezing turns water into
solids
Time
• Bacteria multiply rapidly.
One bacterium can
become one million in
less than seven hours.
• To control bacteria
multiplying you should
• Eat food as soon after it is
made
• Cool quickly and store in a
fridge or freezer.
PH Level
• Bacteria grow best in a
neutral PH between 6.6
and 7.5. They cannot
survive below ph 4.5.
• Ph levels can be
controlled by acidity
regulators which keep
food below ph4.5.
• Vinegar has a ph 3.5
and is used to preserve
foods like onions
Oxygen
• Some bacteria but not
all need oxygen to
reproduce.
• To prevent bacteria
getting oxygen
manufacturers use
vacuum pack foods of a
system known as MAP
where the oxygen is
removed and replaced
with a less active gas.
Cross contamination
• Food handlers need to be very
careful to prevent cross
contamination. This can
happen when
• Raw food touches cooked
• Raw juices drip onto cooked
food
• Hands, knives or chopping
boards not cleaned in
between use.
• Dirty cloths being used to wipe
with
• Dirty towels being used to dry
hands.