Food Preservation Flashcards
(35 cards)
Reasons why food preservation is popular
Allows foods to be available throughout the year.
Preserved foods are easy to store until needed.
Introduces new flavours & variety to the menu.
Reduce waste
Principles of preservation
Inhibits enzyme activity.
Prevents microbial activity.
Can maintain original colour, taste, texture & nutritional value of food.
Sealed containers prevent food from being re-contaminated.
Inhibits enzyme activity
Denatures enzymes, stops enzymes working.
EG: Enzymes break down fish in fridge but are slow breaking down fish in freezer or cooked enzymes are killed.
Prevents microbial activity
Stops moulds, bacteria, & yeast from growing.
EG: Freezing food will take away warmth & liquid water.
Maintains colour, flavour, texture & nutritional value
Aims to keep the original qualities of fresh food.
EG: Freezing is best for this.
Underlying principles of freezing food
Freezing removes liquid water from microbes, changing it to solid ice.
Freezing removes warmth from microbes.
Fast freezing
Tiny ice crystals form, causing little damage to cell walls.
Nutrients are not lost/little amount when thawed.
Slow freezing
Large ice crystals form which damage food cell walls.
When thawed, cell collapses & liquid is lost.
Advantages of freezing
Reduces food waste.
Out of season foods available all year.
Saves time.
Disadvantages of freezing
Cost of buying and running a freezer.
Packaging can be expensive.
Rules for freezing
Thaw fruits in the fridge.
Defrost freezer when stocks are low.
Unsuitable foods for freezing
Lettuce turns mushy & limp.
Bananas blacken due to enzymes.
Whole eggs crack & go gluey.
Suitable packaging for a freezer
Tin foil.
Polythene bags.
Freezer papers.
Labeling frozen foods
Should contain contents, weight, and date of freezing.
Freezer burn
Occurs when cold air has a drying effect on exposed food.
Blanching foods
Involves immersing food in boiling water for a short period.
Method of blanching
Vegetables are put into boiling water to kill enzymes & bacteria.
Methods of commercial freezing
Air blast freezing. Plate freezing
Flow freezing, cryogenic freezing
Air blast freezing
Blast of cold air moves around food on a conveyor belt.
Plate freezing
Cartons of food placed between 2 metal shelves.
Flow freezing
Food is blasted with cold air from underneath a conveyor belt.
Cryogenic freezing
Food is sprayed with liquid nitrogen to create thin ice crystals.
Heat Treatment: Jam Making
Fruit boiled with large amounts of sugar.
Underlying principle of Jam making
Use high heat to denature enzymes & kill microbes. High proportion of sugar is used to remove water from microbes.
