LO: To understand how to answer exam
questions on Food Preservation and Spoilage
Must: Take part in the group discussions and
contribute to the answers given.
Should: Be able to structure an extended answer,
(be able to complete questions starting with
‘explain’, ‘summarise’ or ‘discuss’).
Could: Motivate and inspire others by taking a
leading role within your group.
Food Preservation
• Food is preserved to extend the shelf life of a product (make it last longer)
and to stop it from spoiling (going off).
Food spoilage can be caused by, natural decay, contamination by microorganisms and action of enzymes.
Micro-organisms come in 3 groups:
•
Yeasts - active in warm, moist conditions. Found in the air, soil & skin of
fruit. Able to break down sugars to produce Alcohol and carbon dioxide.
This is known as fermentation and helps when making bread, alcoholic
drinks and yeast extract spreads (marmite, vegemite).
• Moulds - fungi that grow in food. Black, white or blue in colour. Prefer
moist/humid conditions. Can be harmful but can also be used to produce
special types of cheese.
• Bacteria - most active (reproduce rapidly) in optimum temperature of 37
degrees. It is the pathogenic, (bad), bacteria that will cause food poisoning
or food-borne illnesses, resulting in serious illness or even death. Toxins
are the poison that a bacteria produces that cause illness.
There are 6 things that affect the
growth of micro-organisms:
• Time
• Temperature
• Food
• pH
• Oxygen
• Moisture
MAP – Modified Atmosphere
Packaging
• Most of the oxygen is removed from the packet.
• This works because most bacteria need oxygen to
reproduce
• Sometimes a vacuum is used (vacuum packing)
• Sometimes the oxygen is replaced with another
gas e.g. Nitrogen or Carbon Dioxide. This also
alters the pH of the food.
• Examples are salad, bacon, and smoked fish
Chilling / Refrigerating
• This keeps food fresh for short periods of time.
• Chilled food is stored between 1°C and 8°C.
• The best temperature is below 4°C as this will
stop Listeria reproducing.
• Chilled meals must be re-heated to 72°C and
eaten within 2 hours or thrown away. They must
not be re-heated more than once.
• Chilling foods slows down bacteria growth and
enzyme activity. This speeds up again in warmer
temperatures.
Freezing
• This keeps food fresh for longer periods of time.
• Frozen food is stored between -18°C and -29°C.
• There is a high demand for frozen food because it is very
convenient and can last between 3 and 18 months.
• Freezing food causes bacteria to become dormant ,(go to
sleep). As food is thawed (defrosted) the bacteria start to
reproduce again.
• Some people avoid frozen food because they think it loses
taste and nutritional value.
• Freezer burn can affect frozen food that has been stored for
a very long time or is badly packed. The food becomes very
dry and can have white spots or marks on it.
Canning
• Canning is a way of sterilising food to make it last a
very long time (years).
• Food is either sealed in cans and then sterilised, or
sterilised and packed into sterile (germ free)
containers.
• The time and temperatures used depend on the food.
Baked Beans are heated to 120°C for 33 minutes and
then rapidly cooled.
• Once a can is opened spare food may be saved in the
fridge for a couple of days. However, it should be put in
a clean container or dish and never stored in the can
itself.
What is a high risk food?
Egg Products
Gravies and
Soups
Raw or cooked
meat and
poultry
Raw or cooked
fish
Food poisoning bacteria can
grow and multiply on some
types of food more easily than
others. High risk foods are
moist and rich in protein, they
include:
Shellfish
Cooked Rice
and lentils
Prepared
salads
The Danger Zone
The core (middle) temperature of
high risk foods should be 72 °C for
at least 2 minutes
Most bacteria multiply above 5 °and
below 63 °C. Any temperature in this
range is in the danger zone.
High-risk foods are stored below 5 °C and
cooked above 63 °C and cooked to a core
temperature of 72 °C degrees for at least
two minutes.
Frozen foods should be kept below -18°C
Cross Contamination
This happens when food
handlers transfer bacteria
from one food to another.
It can cause food poisoning
and happens when:
Bacteria are carried on
equipment e.g. hands,
dirty cloths, knives and
chopping boards
Liquid or juices drip from
raw food onto a high risk
food
Raw food touches high
risk food
Coloured Chopping Boards and
Equipment
• Using colour coded equipment for different
food helps to prevent cross contamination.
Some Pathogens (bad micro-organisms)
Pathogen
Where found
Clostridium Botulinum (Botulism) Seafood, Canned food, meat,
sausages.
Listeria
Soft cheese, pate, poorly stored
/re-heated ready meals,
unpasteurised milk
Salmonella
Eggs and Poultry
E-coli
Raw Meat
Staph A
Food handlers noses, mouths,
hands and in septic cuts
Bacillus Cereus
Rice, lentils and beans
HACCP
HAZARD
ANALYSIS
CRITICAL
CONTROL
POINTS
A system to make sure food
is produced and stored
safely. Like the Hazard Chart
you produced in your
coursework.
A CCP is a Critical Control Point for example
specified cooking time and temperature. It is
a check put in place at important processing
points to ensure that food is safe to eat.
Types of Contamination
Physical
Chemical
Microbiological
Hair
Bleach
Yeasts
Metal
Detergent
Moulds
Wood
Washing Up Liquid
Bacteria
Plastic
Any cleaning
material
Rubber
Pesticides
Teeth and Bones
LO Review: To understand how to answer exam
questions on Food Preservation and Spoilage
Must: Take part in the group discussions and
contribute to the answers given.
Should: Be able to structure an extended answer,
(be able to complete questions starting with
‘explain’, ‘summarise’ or ‘discuss’).
Could: Motivate and inspire others by taking a
leading role within your group.