What to Use to Pack Food before Freezing
13 September 2009
Freezing is not only an easy way of preserving both raw and cooked food, but it is also completely safe if the rules of hygiene are observed and food is correctly packed. Good food will keep its quality and nutritive value in the freezer, but freezing cannot improve poor quality food.
Basic freezing procedure
- All food for freezing must be processed quickly.
- Food must be thoroughly chilled before being put in the freezer to avoid raising the temperature of food already stored.
- Food must be carefully packed to exclude air, and should be labelled for identification. A simple record of the food in the freezer will aid meal planning and encourage you to maintain a steady turnover.
- Food should be frozen quickly, preferably against the cold surfaces of the cabinet, and at the recommended low temperature.
- Frozen cooked food must never be thawed and then refrozen. Raw materials should not be thawed and refrozen, but may be made into cooked dishes and frozen.
Portions
Food should be prepared and packed in useable portions. Most people find it wise to prepare some large or family-sized packs and also a number of individual packs for use for single meals. Large packs of fruit and vegetables can be re-fastened after portions have been removed. A single portion of food will vary according to whether it is for a small child, a woman or a manual worker. Two people usually eat slightly less than two single portions when together.
Packaging materials
All packaging should be moisture and vapour proof, waterproof and greaseproof; durable and resistant to low temperatures; easily handled, economically stored and free from smell.
Waxed tubs Waxed tubs are available with flush airtight lids and with screw-on tops. Waxed cartons are also made with fitted lids in square and rectangular shapes, and there are tall containers with tuck-in lids, and special ones with polythene liners which are suitable for food subject to leakage.
Rigid plastic containers Most branded plastic boxes are suitable for freezer storage. Those with flexible sides can be lightly pressed to aid removal of contents. Special Swedish freezer boxes are available which can be boiled for sterilization and which stack and save space.
Glass jars Screwtop preserving jars, bottles and honey jars may be used for freezing if tested for resistance to low temperature. Place an empty jar in a plastic bag in the freezer overnight; if it breaks, the bag will hold the pieces. Jars with 'shoulders' should not be' used as this necessitates long thawing before the food can be turned out and used.
If using freezer-to-table ware, remember that it is a bad conductor of heat. This means that dishes are slow in heating but hold their heat for a long time. Allow extra time for water, stock or sauces to reach boiling point, but in all cookery remove from the heat a short while before you would do so in other pans. It is difficult to halt the cooking even after removal from heat; sauces tend, therefore, to solidify or curdle, eggs harden and seared meats burn.
Polythene Polythene bags are useful for almost all freezer food, and are available in a wide variety of sizes; they should be of the special heavy quality designed for low temperatures.
Polythene sheeting is easy to handle for wrapping meat, poultry and pies, and its transparency makes quick identification easy.
Foil and freezer paper Foil dishes are useful for dishes which are cooked before freezing and are later reheated, as one container may be used for all the processes. Heavy duty foil sheeting is useful for overwrapping these dishes, and for packing both raw and cooked foods; it should be used with the dull side towards the food. Freezer paper is strong wrapping which is highly resistant to fat and grease, does not puncture easily, and has an uncoated outer surface on which labelling details may be written. All types of container and sheet wrapping must be firmly sealed. Bags can be closed with fasteners or heat-sealed with a special welding unit, or with a domestic iron used over thick paper. Special deep-freezing tape with gum which is resistant to low temperatures must be used for finishing sheet-wrapped packages and sealing containers with lids.
Headspaceand air exclusion
Containers with lids should be 16 packed so that headspace from 1/2 inch to 1 inch is left above the surface of the food to allow for expansion of contents, according to individual foods.
All sheet wrappings or bags must have the air pressed out so that the wrapping adheres closely to the food When forming a parcel, the air can be pressed out with the hands. Air is most easily removed from bags by the insertion of a drinking straw at the closing, and by sucking the air out just before sealing.
Packaging
To avoid loss of quality, food should be carefully processed, packed, and then thawed or cooked quickly when needed. An enzyme is a type of protein which accelerates the chemical reactions in food. These reactions are slowed down by a freezing process, which is why freezing must be done quickly. Thawing speeds up enzymic reaction. It therefore encourages rapid deterioration, so that food is best thawed in a cold atmosphere such as a refrigerator, and must be eaten or cooked immediately after thawing.
Bad packaging causes a number of problems which does not render the food dangerous to eat, but which may cause an unattractive appearance, toughness and dryness, lack of flavour, or unpleasant mingling of flavours from different foods. Some of these are:
Dehydration and freezer burn Long storage and poor wrapping may result in the removal of moisture and juices, particularly from meat. This sometimes causes greyish-brown areas on food known as 'freezer burn'.
Oxidation and rancidity Oxygen from the air which penetrates wrappings reacts with fat cells in food to form chemicals which give meat and fish a bad taste and smell. Fried foods and fat meat and fish can suffer from this problem in the freezer. Salt accelerates this rancidity.
Broken packages and cross-flavourings Rough handling, sharp edges, brittle wrappings or overfilled containers may cause cracks or breakages which will result in dehydration or oxidation. This can also result in cross-flavouring with strongly-flavoured foods, which may also spread smells and flavours if packages are not very strong or overwrapped.
Flabbiness Limp and flabby fruit and vegetables are caused by slow freezing, and sometimes by the choice of varieties unsuitable for freezing, which must be subject to trial and error.
Ice crystals If too large a headspace is left on liquid foods in containers, a layer of ice crystals may form which will affect storage and flavour. Liquids can be shaken or stirred back into emulsion when heated or thawed. If the problem occurs in meat, fish, vegetables or fruit, it is usually because the food has been slow-frozen so that moisture in the cells has expanded and frozen and broken surrounding tissues. This results in juices and flavour being lost.
Cleaning and defrosting
Defrosting is normally carried out when ice is 1/4 inch thick. Manufacturers' instructions should be followed for occasional defrosting but build-ups of ice may be removed with a plastic scraper. Sharp tools or wire brushes should not be used. For complete defrosting, food should be removed to a refrigerator or wrapped in layers of newspapers and blankets in a cold place. After defrosting, the freezer should be wiped completely dry and run at the coldest setting for 30 minutes before replacing food. The machine should then continue to run at the coldest setting for a further 2 1/2 hours before the switch is returned to normal setting.
The inside of the freezer is best cleaned with a solution of 1 quart water and 1 tablespoon bicarbonate of soda; the water should be lukewarm. Soap, detergent or caustic cleaners must not be used. The outside of the cabinet may be cleaned with warm soapy water and polished with enamel surface polish.
Power failure
When power fails, the freezer is best checked first for local causes. The switch may have been turned off by mistake, or the fuse in the plug may have 'blown'.
The cabinet should be left shut when power has failed, so that the cold temperature is retained. Properly packed food will last about 12 houts safely, although this depends on the load of food and on insulation. A fully-packed freezer will maintain a low temperature for a long period.