Food Refrigeration and Freezing

14.1 I NTRODUCTION

The present-day food industry is almost totally dependent on refrigeration in one form or another, to manufacture, preserve, store and bring the product to the point of sale. Chapter 16 gives some examples for specific food products, whilst this chapter gives an overview of cooling methods.

The use of low temperatures for food preservation has been known and practised for many thousands of years, but it was not until the mid-nineteenth century that Pasteur and others determined the bacteriological nature of food spoilage and the beneficial effect of cooling which slows chemical reactions and breakdown by bacteria. Mechanical refrigeration made it possible to pro­vide the extra food required by the growing urban populations. A large inter­national trade was built up, starting with the transport of frozen meats to Europe in 1873 and 1876 from Australasia and South America.

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 to a temperature low enough to significantly reduce the amount of free moisture and hence bacterial activity. Until the temperature is reduced below the minimum temperature for growth, some microorganisms can potentially multiply.

A distinction must be drawn between the cooling process and the subse­quent storage. Careful control of temperature and humidity is needed when cooling warm produce since evaporative cooling plays a part in both product temperature and weight loss. 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.

Cooling and freezing cannot improve a fresh vegetable, fruit or meat prod­uct, and the best that can be achieved is to keep it near to the condition in which it entered the cooling process. This means that only the best produce should be used, and this should be as fresh as possible. However sometimes preserva­tion in cold stores is essential to prevent wastage, regardless of the quality of the crop.

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