Food Technology- Preservation


GCSE and AS level food technology revision
Note by evie.daines, updated more than 1 year ago
Created by evie.daines about 10 years ago

Resource summary

Page 1

ENZYMES:They are chemical catalysts found in all cells.they break animal and plant tissue causing: Fruit to ripen meat to tenderise oxidation However if the enzymes continue to work food is spoiled.

OXIDATION OR ENZYMIC BROWNING:Oxidation is when the flesh of fruit turns brown. It can be prevented by: Adding acid (like lemon juice) blanching (boiling water destroys enzymes) Contact with air prevented (good old clingfilm!)

MICROORGANISMS:Yeasts: Single celled organisms that are found naturally on the skin of fruits and in the air. They're also grown commercially and sold.USEFUL: make a variety of products: bread, beer and wine.NON-USEFUL: Can spoil fruits and jams. The food would have an altered taste.

Bacteria: Single celled organisms which are everywhere, even though they cannot be seen,USEFUL: Needed in the food industry, mainly in the production of yoghurtHARMFUL: bacteria which causes food poisoning.

Moulds: Fungi which grows from 'spores' found in the air. They settle on food products and multiply. When they're visible the food is describe as being 'mouldy'.USEFUL: Deliberately used in the food industry, used in quorn and cheese.HARMFUL: cause food spoilage


FOOD POISONINGStaphylococcus Aureus: Found due to food handlers poor hygieneBacillus Cereus: Found in cooked rice, lentils and beans.E-Coli: Found in raw meat.Listeria Monocytogenes: Found in soft cheeses and incorrectly heated cook-chill meals, also meat which is no cooked through and in unpateurised milkSalmonella: found in poultry and eggs


CROSS CONTAMINATIONIt occurs when: raw food touches high risk foods liquid or juices from raw foods drip onto another. bacteria are carried from one food to another by hands, knifes, chopping boards or dirty cloths.

The symptoms of food poisoning include: diarrhoea Vomiting stomach cramps fever  headaches.


Conditions for Bacteria growth: TIME: bacteria is able to multiply TEMPERATURE: bacteria grows best at 37oc. however they produce quickly at any temperature between 5oc and 62oc MOISTURE: They like these condition and most foods naturally have these conditions PH LEVEL: bacteria grows best in neutral PH OXYGEN: Some bacteria (not all) require oxygen to reproduce.

HIGH RISK FOODS: Raw or cooked meat raw or cooked fish egg products cooked rice and lentils gravies and soups



M.A.P and removal of airremoving air and sealing bacteria means bacteria is not able to grow.

Removal of moistureall micro-organisms need moisture, and without it they can't survive.

AdditivesChemical preservatives destroy bacteria and prevent them reproducing.

Irradiationbacteria is destroyed, but it has limited use in the UK

Reducing Heatbacteria are unable to grow in low temperatures. they reproduce at a slower rate until they become dormant (hibernating) they come back to life after defrosting.

Application of HeatMicro-organisms are destroyed at high temperatures.

Methods of Extending the shelf-life of foods are by lowering the temperature are: Chilling, cook-chill, freezing and AFDCold temperatures slow down the speed that bacteria reproduces but does not destroy it.very low temperature cause bacteria to be formant or inactiveHowever as the food warms up, the bacteria begins to reproduce again.

CHILLINGFood is kept in good condition for a short period of timechilled foods are stored between 1oc and 8oc. the optinum chilling temperature is 4oc as it prevents the growth of listeria monocytogenes chilling causes enzyme activity to be reduced

COOK-CHILLING Prepared dishes are cooked and them cooled between 0oc and 9oc food is stored in a refridgerator at a temperature between 0oc and 3oc they have a shelf life of 5 days, including the day they were made. they have to be heated to at least 72oc before being eaten they should be eaten within two hours and left overs thrown away they shouldnt be re-heated

FREEZING commercially frozen food can be quick frozen. quick freezing reduces cell damage in the food it is then stored in the freezer between -18oc and -29oc there is a high demand for frozen food.

ACCELERATED FREEZE DRYING (AFD) its a combination of freezing and drying food is quick frozen then placed ina vacuum. on heating the food is left dry


HIGH TEMPERATURE METHODS: pasteurisation sterilisation ultra heat resistant canning irradiation

Pasteurisation: Liquid is heated and held at a high temperature for a short time The temperature and time vary on the liquid being heated pasteurisation is a short time preservation it only kills some bacteria

Sterilisation: Food is heated to high temperatures in high temperatures and held for a long time caramelisation occurs this changes the flavour of the product it destroys most bacteria it is used in a wide variety of food

Ultra heat-treatment (UHT) Liquid is heated to high temperatures for a short period of time it is a long term method of preservation it causes no change to the flavour of the product it kills bacteria

Canning it is a form of sterilisation Food can be packed in cans or bottles or pakced into aseptic containers the containers are sealed to prevent re-contaminatiob

Irradiation uses ionising radiation from electron beams or gamma rays the food absorbs energy allowing radicals to develop radicals destroy bacteria this is a new form of processing into the Uk  NOT THE SAME AS RADIATION

ADDITIVESThe ingredients by law must be added in descending weight orderThe 'E' number is a code used instead of chemical names which are long and complicated

Colours (E100s)Give colour to food

Preservatives (E200s)Keep food safe to eat for longer by stopping the growth of bacteria

Emulsifiers and Stablisers (E400s)Prevent emulsions seperating

Antitoxidants (E300s)Prevent fats going rancid through oxidation. they help slow down the browning of fruit.

Commonly used additives: Sweeteners flavourings flavour enhancers thickening/gelling agents




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