This document provides information on freezing as a method for food preservation. It discusses the principles and advantages of freezing, suitable and unsuitable foods for freezing, packaging and storage guidelines, and specific instructions for freezing and thawing. Freezing works by lowering the temperature of food to inactive microbes and enzymes. It maintains quality if food is quickly frozen and properly packaged and stored. Common foods frozen at home include meats, fruits, vegetables and baked goods.
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.
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.
