FOOD PRESERVATION

FREEZING

© PDST Home Economics

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.

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.

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.

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.

(i) FREEZINGPRINCIPLES

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.

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.

                            

                                                                          

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.

FREEZINGSUITABLE 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.

RULES FOR FREEZINGPREPARATION

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.

RULES FOR FREEZINGPACKAGING

Pack in usable quantities. Use strong, vapour and moisture proof

packaging. Allow expansion room in liquid foods. Label food with name, quantity & date.

RULES FOR FREEZINGFREEZING 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.

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.

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.

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.

STORAGE TIMES

Chicken 12 months Vegetables 12 months Beef 12 months White fish 6 months Cooked pastry 6 months Lamb 6 months Oily fish 4 months Soups sauces 3 months Mince meat 3 months Casseroles 2 months Bread 1 month

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.

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.