Freezing Technology

6.2.1 Refrigerated Containers

In a refrigerated transport container or insulated vehicle it is difficult to maintain a low and stable produce temperature. Added to this, the effect of fans, the opening of the door and the presence of workmen is proportionately greater in refrigerated transport than in a large, well-designed storage chamber. Under operating conditions the best temperature obtainable is approximately -18⁰C to -15⁰C.

It follows that produce should be kept in transport vehicles and containers for as short a time as possible. Very often parked containers are used for cold storage to avoid the expense of constructing a cold store. However one has to keep in mind that parked transport containers and vehicles are not suitable for use as stores for frozen produce except for very short periods and in emergencies. There is such greater risk of loss of quality through temperature fluctuation and desiccation in refrigerated containers than in large, well-designed and well-operated cold store. Storage in transport containers is also very expensive when compared with properly designed cold stores.

The Cold Chain

Temperature is the single most important factor influencing fish spoilage. The cold chain is a temperature chain. It means 0⁰C for fresh fish and -20⁰C for frozen fish from the producer to the consumer. Temperature rise and temperature fluctuation will accelerate quality deterioration and it should to be avoided. Especially sensitive to temperature abuse are fresh, live and lightly cured (e.g. smoked fish) products. These should be kept at 0-1⁰C, and their temperature should never rise above 3⁰C.

Temperature fluctuations accelerate the reformation of small ice crystals into larger crystals damaging the cells. Also, desiccation will increase because of temperature fluctuations.

The insulated transport vehicles and containers shall be provided with  adequate quantities of coolant or good mechanical refrigeration. Refrigeration requirements vary considerably depending on the duration of transportation, the temperature at which a product has to be maintained, the quality of insulation material, the dimensions of a container and the temperature of the environment.