Food preservation freezing

not mine
by pdst.ie

1. FOOD PRESERVATION
FREEZING
© PDST Home Economics

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
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

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.