Food AS - Conditions and factors for the growth of bacteria
Raw and cooked foods
Bacteria will grow in both. Raw meat and poultry will contain bacteria. Most meat is COOKED, during the COOKING PROCESS bacteria are DESTROYED, making the FOOD SAFE.
At what temperature does bacteria become dormant?
Below 5C, most bacteria are UNABLE to MULTIPLY RAPIDLY. Dormant = a period of INACTIVITY when bacteria are UNABLE to MULTIPLY. Bacteria CAN SURVIVE the FREEZING PROCESS.
What temperature will bacteria grow very fast?
Between KITCHEN temps (20C) and BODY temp (37).
Why should food be stored at the correct temperature?
CONTAMINATION after cooking is possible.
What conditions does bacteria like?
NEUTRAL conditions a pH value of 7 or slightly alkaline conditions of pH 7.4. Bacteria will not grow in foods with a pH below 4.5.
What is a bacterium?
ONE bacteria. A bacterium DIVIDES into TWO by a process called binary fission. Needs only 12 hours to have produced a colony of 16 million.
What can high qualities of sugar and salt do?
They can ABSORB WATER from PLANT and ANIMAL CELLS. BACTERIA CANNOT SURVIVE in these conditions so JAM MAKING reduce the likelihood of bacterial contamination.
Oxygen - anaerobes
Those that DO NOT NEED OXYGEN are called ANAEROBES such as Clostridium perfringens. Anaerobes can SURVIVE in VACUUM-PACKED food products. Bacteria will GROW or SURVIVE with or without oxygen, e.g. Salmonella.
Oxygen - aerobes
Those that NEED OXYGEN are called AEROBES such as Bacillus cereus.
What temperature will destroy most bacteria?
When COOKING FOOD at temps above 63C. To ensure temp is high enough, check the CORE of the product reaches 70C at for atleast 2 MINS.
Time
When bacteria are left in WARM, MOIST, PROTEIN-RICH conditions for a LENGTH OF TIME, they can REPRODUCE RAPIDLY. Under these conditions, the numbers of bacteria can DOUBLE EVERY 20 MINUTES. Meaning within a FEW HOURS, a few bacteria can increase enough to make the FOOD UNSAFE to EAT.
Reconstituting a dried food
With WATER/MILK will make IDEAL CONDITIONS for BACTERIAL GROWTH.
What can't bacteria do without moisture?
MULTIPLY and cause food poisoning. This is why DRY FOODS aren't usually affected by food poisoning.
What are acid conditions?
pH 0 to 7.
What are alkaline conditions?
pH 7 to 14.
Cold food combining with warm food
TOPS UP the temp and can bring FOOD BACK into the DANGER ZONE and increase the risk of BACTERIA MULTIPLYING.
Spores
Able to be formed by BACTERIA and when CONDITIONS IMPROVE they will become ACTIVE and start the process of MULTIPLICATION.
Food poisoning bacteria have four essential requirements, what are these?
A FOOD SOURCE. WARMTH. MOISTURE. TIME. Some also require oxygen.
What temperature will most bacteria multiply at?
AMBIENT temperatures - NORMAL ROOM TEMP and is within the DANGER ZONE. Danger zone is between 5C and 63C and will allow bacteria to GROW.
Humidity
AMOUNT of WATER in the AIR. DRIED FOODS can be contaminated with with MOISTURE in HUMID CONDITIONS. Kitchen can be a very HUMID PLACE.
What bacteria can produce spores?
Clostridium botulinum, Clostridium perfringens and Bacillus cereus.
What are the types of foods which bacteria can grow easily?
Cooked meat and poultry. Shellfish and seafood. Uncooked or lightly cooked eggs. Gravies, sauces, soups and stocks. Cooked rice and pasta. Prepared salads.
How must dried foods be stored?
DRY, WELL VENTILATED and COOL areas.
Foods that are eaten raw, cooked/ready to eat
GREATER RISK of food poisoning. These foods have been HANDLED more during PREP and PRODUCTION.
Food
Required by BACTERIA. Food in which bacteria grows RAPIDLY is called high-risk food. Bacteria nee foods which are GOOD SOURCES of PROTEINS.
