Refrigerator

A major use of refrigeration is in the preservation, storage and distribution of perishable foods.

A very large variety of self-contained refrigeration and air-conditioning packages are made, mainly for the consumer durable market and small domestic applications. They include:

1. The domestic refrigerator and freezer.

2. Ice-cream conservators.

3. Retail display cold and freezer cabinets and counters.

4. Cooling trays for bottles (beer, soft drinks, wines).

5. Instantaneous draught beer coolers. These usually comprise a tank of constantly chilled water, through which the beverage flows in stainless steel piping.

6. Ice makers – cubes and flakes.

7. Cooled vending machines.

8. Soft ice-cream freezers.

9. Dehumidifiers, in which air is passed first over the evaporator to remove moisture, and then over the condenser to re-heat and lower the humidity.

10. Drinking water chillers.

The edibility of foodstuffs is prolonged by lowering the temperature, since this slows chemical reactions and breakdown by bacteria. Some products can be frozen, and when they are in the solid state all movement in the individual cells will cease, inhibiting further reactions.

The decision whether to just chill or to freeze solid depends on the type of product and the length of time it must be stored. Freezing results in some structural change, since ice crystals are formed inside the cells, and the final foodstuff may be of different texture when thawed out.

As a general rule, foods which are not to be frozen are handled and stored at a temperature just above their freezing point, providing this does no damage (exceptions are fruits such as bananas and lemons). Produce which is to be frozen must be taken down below the freezing point of the constituents. Since foodstuffs contain salts and sugars, the freezing process will continue down to –18°C and lower.

A distinction must be drawn between the cooling process and subsequent storage. Careful control of temperature and humidity is needed when cooling warm produce, or there may be serious losses in weight and quality. Considerable research has been carried out to find optimum methods for different foodstuffs, especially meats, for cooling and for short-term and long-term storage.

All foods must be clean on entry. Some, such as fish, leaf vegetables and some fruits, may be washed and left wet. Fish will tend to dry out and lose its fresh appearance, so it is packed wet or given a sprinkling of ice chips to keep the surface moist. Other products, especially the meats, must be dry, or bacteria will live on the moisture and make the skin slimy. Potatoes will start to sprout after a long period in storage. This can be checked by spraying the freshly lifted tubers with a chemical sprout depressant.

Certain fruits, notably grapes and dates, may have some surface contamination or infestation when first picked, and they are fumigated with sulphur dioxide or some other gas. They must, of course, then be thoroughly ventilated before going into storage.

Handling conditions must be hygienic. Some types of food, such as milk, can be kept sealed within the processing system. If the food will be exposed to the air during handling, the conditions of the surrounding air – in terms of temperature, humidity and cleanliness – must be the best that can be maintained. This is especially the case with fresh meats.

Most products will keep longer and fresher in the frozen condition, and this process is used for those whose sale value will support the extra process cost. The cells of animal and vegetable products contain a watery solution of salts and sugars. If this solution starts to freeze, surplus water will freeze out until the eutectic mixture is reached.

If freezing is not carried out quickly, these ice crystals will grow and pierce the cell walls; then when the product thaws out, the cells will leak and the texture will be spoiled. This is of no great consequence with the meats, whose texture is changed by cooking, but will not be suitable for fresh fruits or vegetables. As a general rule, any product which will be eaten without cooking, or only very brief cooking (such as green peas), should be quickfrozen in a blast-freezing tunnel or similar device. Other foodstuffs need not be frozen so quickly, and may be left in a coldroom at a suitable temperature until frozen. Frozen confections (ice-cream and ice-lollies) rely on speed of freezing to obtain a certain consistency and texture, and they require special treatment.

Once a product has been frozen, it must never be allowed to warm and then be re-cooled, or partial thawing may take place with slow re-freezing.

Cold storage packing must contain and protect the product, while allowing the passage of cooling air to keep an even temperature. Packages generally will be small enough to be lifted by hand if required, and of a suitable shape to be stacked on pallets for mechanical handling by fork-lift trucks. Stacking on a pallet should allow the passage of air between the individual packs. Fruits and vegetables which give off heat of respiration need to have perforated cases so that air may pass through the product.

Top-freezer and bottom freezer refrigerators generally give you more usable space for your money than comparable side by sides. And they costs less to run. Frigidaire, GE, Kenmore(Sears) and Whirlpool account for almost 60 percent of top freezer refrigerator sales. For side by side models, these brands and Amana account for more than 80 percent of sales. Brands offering bottom freezer models include Amana, GE, Kenmore and kitchen aid. Mainstream manufacturers have launched high end sub brands such as GE profile and Kenmore Elite.