Brief Guide to Freezers

Freezers have been part of domestic life in the Western World since the 1950s. But in fact freezing as a way of food preservation is very old indeed  practised for thousands of years by the Inuit (Eskimo) and other northern peoples wherever the winter was long enough to make use of ice holes or ice caves. We have since learnt that freezing can preserve food because the intense cold inhibits the spoiling activities of bacteria, yeasts, moulds and enzymes. The modern freezer, which keeps food consistently at about 18ºC (0ºF), is simply a way of bringing the benefits of these extreme weather conditions into our homes.

Freezers offer an effective and economic way to preserve food for several months. This is particularly useful for food that would otherwise spoil, even in a refrigerator. It means that you can cook or buy in bulk, and freeze what you don't want to use immediately. This makes sense economically (freezers cost very little to run), and for food planning. Almost all foods can be frozen, although some (such as fresh fruit and vegetables) may need some preparation.

• See an irresistible multi-buy bargain in a food shop? Buy it and freeze it.
• Lots of leftovers from a dinner party? Freeze them for another occasion.
• Want a constant supply of apple purée/cooking stock/soup/chicken tikka masala? Buy or make it in bulk and store it in usable portions in your freezer.
• Going on holiday? Transfer the perishable contents of your fridge to the freezer.
• Too big a crop from your vegetable garden? Freeze the excess.

Freezing causes the water content in the food to turn into ice crystals. It is this process that puts it beyond use of the bacteria, moulds and enzymes. But it also makes the water expand, damaging the cell walls in the food, and thus changing its texture. Freezing also diminishes to a small extent the nutritional value of the food, and its vitamin and mineral content  although the 'Fast Freeze' option (or 'Automatic Fast Freeze'), provided by many of the more expensive freezers, minimises this deterioration. Whatever the case, freezing certainly cannot be said to improve the taste of food.

There are two main types of freezer: chest and upright. Upright freezers are rather like refrigerators, and a small one can easily fit into a kitchen alongside other appliances. Uprights contain a number of shelves or drawer-like wire baskets. One disadvantage is that the cold air tends to spill out when the door is opened, but this problem is reduced in models that have doors to each shelf, or solid-sided drawer-like 'buckets' instead of wire baskets. Chest freezers have a hinged lid on the top; they tend to be bigger than upright freezers, and for this reason are often housed outside the kitchen in a cellar, or utility room, or garage. They are best suited to big households stocking large quantities of food, or to people who produce prodigious quantities of fruit or vegetables from their garden, or who like to freeze the products of their hunting or fishing, or who like buying bulk supplies of a product when available (such as half a sheep from an organic farm). Chest freezers are a little harder to manage than upright freezers, because the containers of food tend to pile up on the bottom, even if the suspended wire baskets do go some way to alleviating the problem. It is hard to recommend what size of freezer to buy: it depends entirely on your own individual habits of shopping and eating  or what you think they might be once you've got a freezer. When measuring up the space where you are going to put your new freezer, remember to allow a gap of 25mm (1 inch) on all sides, as the condenser gives off warm air which needs to disperse.

New freezers are graded by manufacturers on an Energy Rating scale of A (and A++ and A+) to G, with A++ being the most energy-efficient. These assessments are monitored by the Trading Standards Institute. In any case, the running costs of freezers are low, typically about £25 a year, or less. Freezers are more efficient when full, as the bulk of frozen goods helps maintain a low temperature. Nowadays, new freezers do not contain ozone-damaging CFCs (chlorofluorocarbons), and many are free also of HFCs (hydrofluorocarbons), which may contribute to global warming. Instead, they use the natural gas propane, a hydrocarbon that does not harm the ozone layer and makes minimal contribution to global warming. When getting rid of your old freezer, see if the company supplying the new one can dispose of it safely for you; otherwise, contact your local recycling centre for advice.

You can freeze virtually any sort of food, but some types of food stand up to this treatment better than others. Best of all are cooked dishes, such as stews, puréed fruits, sauces, soups and stock. Fresh meat and fish freeze well, but will suffer from some deterioration in texture. Most fresh vegetables have to be blanched (plunged into boiling water for three or so minutes then cooled rapidly in cold water), before freezing. Some vegetables that are eaten raw (such as lettuce, cucumbers, cress and radishes) are unsuitable for freezing at all: they just become limp and soggy. Boiled or baked potatoes turn crumbly and floury. Most fruits have to be cooked, or partially cooked, before freezing; some berries, however, (such as raspberries, blackberries and blueberries) can be frozen raw by first arranging them separately on a tray in the freezer, then packing them loosely in bags or boxes once frozen. Milk sauces and cream may separate or go lumpy with freezing. Bread freezes well; sliced bread separates easily when frozen, so can go straight from the freezer into the toaster  a useful way to keep bread fresh when your consumption is moderate.

Plastic containers with tight-fitting lids work best for foods with a high liquid content. Remember to leave at least half an inch at the top, as water expands when frozen. Use containers of a moderate size (up to 5 litres, or 8 pints): the freezer may not be able to reach the heart of larger containers packed with food, and in any case you will have to thaw the entire contents to use just a part. Plastic freezer bags (available in rolls in supermarkets) are a cheap and effective way of storing both solids and liquids; they can be easily sealed with the wire twist tie that comes with them. Aluminium foil can also be used to wrap items for the freezer. You can freeze cooked dishes in glass or pottery dishes: be aware, though, that the contents won't be easy to remove until thawed. Remember to write on each container or bag (with a permanent felt-tip pen, or a sticky label) both what it contains, and the date of freezing. It is amazing how difficult it is to identify unlabelled frozen food: is this meat stew, or plum compote?

You should label your food with the date because freezing is only a temporary means of preserving food, not a permanent one. Freezing works as a method of food preservation because it severely retards the spoiling activities of micro-organisms, but it does not eliminate it entirely. As rule of thumb, you can keep vegetables and fruits in the freezer for 812 months, whole pieces of meat for 69 months, ground meat for 34 months, and fish for 34 months. Fatty meats (such as bacon) have the shortest freezer shelf-life (up to 2 months), because fats tend to become rancid under freezing conditions. After several months, the food will exceed its shelf life and become hazardous. These guidelines only apply if the food is kept consistently at a temperature of 18ºC (0ºF) or lower (which is the standard temperature for conventional, Four-Star rated freezers); it will last less long if the temperature fluctuates because the freezer door is opened too frequently, or if too much unfrozen food is added to the freezer in one go, causing the freezer temperature to rise.

Freezing does not destroy damaging micro-organisms: they just go dormant. You have to remember this in particular when thawing frozen food. Many foods (vegetables, prepared cooked foods, commercially-prepared frozen dishes) can be cooked straight from the freezer, without thawing. But some  especially fresh meat (and particularly poultry) and fish  must be thoroughly thawed before cooking, to ensure that the cooking process (which will kill any bacteria) is not inhibited by the presence of ice. Micro-organisms start multiplying and become seriously active at any temperature above 4.5ºC (40ºF), which is just above normal refrigerator temperature. It is better therefore to thaw food in a refrigerator  but this takes much longer than thawing at room temperature. If you thaw at room temperature, you run the risk of encouraging bacteria  so due care must be taken (for instance by making sure thawed poultry is very thoroughly cooked.) Another safer alternative is to thaw frozen flood in running cold water. Small items can also be thawed in a microwave, but microwave thawing is a bit hit-and-miss, and by the time the process has penetrated the middle, the outer parts may be cooking. This is fine, however, if you want to cook the food fully immediately after thawing.

For the reasons given above, as a general rule, if the thawed item has reached a temperature of 4.5ºC (40ºF) or more, then you should not refreeze it without first cooking it. If in doubt, do not refreeze. You should never refreeze ice-cream that has melted (instead, put it back in the freezer immediately after serving). An exception can be made for frozen bread: it can be thawed and refrozen without harm, provided that it has not acquired moulds in the meantime.

Freezers generally look after themselves well enough, but over time frost and ice may build up on the freezing elements and shelves. This makes the freezer less efficient, and takes up valuable space. The freezer will then need to be defrosted. ('Frost-free' freezers should not need this treatment, but may need to be defrosted for cleaning.) For defrosting, follow the manufacturer's instructions. Generally the pattern goes as follows. First remove all the items in the freezer, and keep them frozen by wrapping them in newspaper, and sealing them in cardboard boxes; or put then in insulated cooler boxers; or give them temporary lodgings in a neighbour's freezer. Disconnect the freezer from the electricity supply, then wait for the frost to melt. Put trays and cloths at the base of an upright freezer to catch the meltwater. The manufacturer may also suggest that you speed up the process by placing an open bowl of boiling water in the base of the freezer. Once the frost has melted or loosened, you can remove all the debris, and wipe the surfaces clean, leaving them dry. Then you can start up the freezer again. Wait half an hour or so until it is fully cold before putting your frozen food back in.

If you have a power cut, or the freezer breaks down, the items within the freezer should remain frozen and safe for up to 48 hours  provided that you do not open the door. After 24 hours, however, you should work out a strategy for moving the food.

• Do not put a large number of unfrozen items into the freezer all at the same time; this will raise the temperature within the freezer, and of the frozen items already in there.
• When putting unfrozen food into the freezer, allow space around it, to enable cold air to circulate, and to prevent it from raising the temperature of neighbouring frozen items.
• Remember that frozen food is very difficult to cut or break or separate. Before you freeze any large item, break it down into the sizes that you will want to defrost and use at any one time.
• If you have a large freezer, it may be helpful to keep an inventory of the contents on the door, so that you know what is in there, and what is reaching the end of its freezer shelf-life.
• Try to keep your freezer full: wasted space in a freezer is wasted energy.
• If using the freezer to cool wine quickly, set a timer (to half an hour) to remind you: if you forget the wine, the bottle will break.

In the 19th century, industrialists set themselves the challenge of emulating freezing conditions for the year-round warehousing and transport of food on ships and trains. They used all kinds of methods: natural ice, chemicals, air-cooling with mechanical pumps. It was only with the aid of electricity in the early 20th century that freezers became more effective and efficient, and thus more widespread among commercial enterprises. In around 1912, the American Clarence Birdseye (18861956) noticed how the Inuit (Eskimo) people in Labrador, Canada, used a method of freezing fish in the cold air, and he developed his patented method of fast-freezing all kinds of food during the 1920s. His innovation was a breakthrough because only tiny crystals of ice formed, so little damage was done to the cell structure (and hence texture) of the food. He sold his business to the Postum Company, which shortly thereafter became General Foods. The socialite heiress and founder of General Foods, Marjorie Merriweather Post, was married to the US ambassador to Moscow; she installed a commercial freezer in the embassy in the late 1930s, as a means of beating the limitations of Russian food and securing good produce all year round. It was a success, and back in the USA, she developed the idea of frozen food for the domestic market under the Birds Eye brand. Freezers caught on in the USA in the 1940s, initially as luxury novelties, but soon as an almost essential tool for running an efficient and economic household.

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