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Presentation on theme: "FOOD PRESERVATION FREEZING © PDST Home Economics."— Presentation transcript:


2 METHODS OF PRESERVATION  Correct storage and cooking of food prevents spoilage in the short-term.  Long-term storage requires one of the following methods: Freezing, Heat Treatments e.g. Canning or Jam, Drying, Chemical Preservation, Fermentation (pickling), Irradiation.

3 WHY PRESERVE FOOD (ADVANTAGES)  Saves money, home preserves cheaper.  Avoids waste.  Food available out of season.  Variety in the diet.  Preserved food can be more convenient.  Preserved foods can be transported long distances.  Creates new flavours, salting, smoking, jam etc.

4 GENERAL PRINCIPLES OF PRESERVATION  To destroy or inactivate enzymes.  To destroy or inactivate micro-organisms.  To prevent the re-entry of new microbes by sealing food.  To maintain the nutritive value, colour, flavour, texture of the food as far as possible.

5 PRESERVATION OF FOOD IN THE HOME Food can be preserved at home by:  (i) freezing,  (ii) jam making,  (iii) making chutney or pickles,  (iv) bottling fruit,  (v) drying.

6 (i) FREEZING PRINCIPLES  Lowering the temperature of food so that microbes and enzymes are inactivated.  Moisture is changed to ice and microbes become inactive without water.  Packaging food maintains the colour, flavour and texture.  Fast freezing (-25ºC) helps maintain nutritive value and texture of food.

7 QUICK & SLOW FREEZING  Quick or fast freezing occurs at –25ºC or less. Ice crystals are small and do not damage food cells.  Slow freezing occurs at -24 ºC or above. Ice crystals are big and damage the food cells causing loss of texture, nutrients, colour & flavour on thawing.

8 FREEZING ADVANTAGES  Simple, safe.  Suitable for lots of different foods.  Best method for maintaining colour, texture, flavour and nutritive value.  Leftovers can be frozen – prevents waste.  Bulk cooking and freezing save time and fuel.  Frozen food is handy for emergencies. DISADVANTAGES  Cost of freezer and running cost.  Space needed for freezer.  Must follow rules for freezing and thawing for food safety.  Defrosting freezer takes time & effort.  Some damage to texture of food.

9 FREEZING SUITABLE FOODS  Fruit & vegetables.  Meat, poultry, fish- both raw & cooked.  Pastry & dough.  Baked foods e.g. bread, cakes.  Soups & sauces.  Cooked meals e.g. lasagne, stew, quiche. UNSUITABLE FOODS  Whole eggs in shells.  Some vegetables e.g. lettuce cucumber, peppers.  Some fruit e.g. bananas, melons, pears.  Mayonnaise, un- whipped cream, milk.

10 RULES FOR FREEZING PREPARATION  Turn on fast - freeze 3 hours before the food goes in.  Only Freeze 1/10 of total freezer capacity at one time.  Fresh food.  Cool food.  Blanch vegetables first to destroy enzymes.  Open - freeze food to prevent sticking then pack e.g. berries.

11 RULES FOR FREEZING PACKAGING  Pack in usable quantities.  Use strong, vapour and moisture proof packaging.  Allow expansion room in liquid foods.  Label food with name, quantity & date.

12 RULES FOR FREEZING FREEZING THE FOOD  Place in fast - freeze compartment, touching base or sides - don’t over pack compartment.  Leave for 24 hours.  Then remove frozen food & place in storage sections.  Turn off fast - freeze button.

13 RULES FOR FREEZING STORAGE  Store similar food together.  Store for recommended time.  Use in rotation.  Keep freezer filled - reduces running cost.  Avoid opening the door unnecessarily.

14 RULES FOR FREEZING THAWING FOOD  Read instructions on commercially frozen food.  Cook vegetables from frozen.  Thaw meats completely, preferably in fridge overnight. This reduces loss of juices/nutrients.  Never refreeze thawed food.  Be careful of drip from thawing food e.g. meat - it can contain live microbes.  Bread and cakes can be thawed at room temperature.  Use fruit partially frozen.

15 SUITABLE PACKAGING MATERIALS PROPERTIES  Strong.  Water proof.  Vapour proof.  Grease proof.  Easy to use.  Sealable. EXAMPLES  Strong, polythene freezer bags.  Aluminium containers.  Aluminium foil.  Freezer paper.  Waxed cartons.  Plastic boxes with tight lids.

16 STORAGE TIMES  Chicken12 months  Vegetables12 months  Beef12 months  White fish6 months  Cooked pastry6 months  Lamb6 months  Oily fish4 months  Soups sauces3 months  Mince meat3 months  Casseroles2 months  Bread1 month

17 BLANCHING VEGETABLES  Equipment: Large saucepan. Wire basket or colander. Large bowl.  Prepare 5 litres of boiling salted water.  Prepare and chop vegetables.  Blanch 500g of vegetables at a time.  Time from when water re-boils e.g. carrots 4 mins.  Plunge into ice-cold water for same time as for blanching.  Drain well and freeze.

18 FREEZER BURN  If protein food is not wrapped properly the cold air will cause the food to toughen, discolour and dry out. This is called freezer burn.

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