|15.1 Definition of "highly perishable"|
|15.1.1 "Plus" goods|
|15.1.2 "Minus" goods|
|Chilled and frozen goods are predominantly foodstuffs which have their origins in the animal or plant kingdom. Foodstuffs may rapidly lose quality at normal temperatures, overripeness, shriveling, mold, rot, loss of aroma and vitamins, rancidity and formation of toxic substances constituting typical changes which within a short time impair the enjoyment of foodstuffs or render them inedible. For this reason, they are known as highly perishable foodstuffs. Their shelf life, quality and freshness may be maintained for an extended period by applying chilling or freezing technology.
Foodstuffs are divided into three groups in accordance with the human body's nutritional requirements:
They include vegetable products, e.g. bananas, pineapple, citrus fruit, pomaceous and stone fruit, berry fruit, vegetables, potatoes and onions, and animal products, e.g. meat, fish, eggs, fats and cheese.
In fruits and plant parts which have been separated from the parent plant, degradation processes predominate, their supply of new nutrients having been cut off.
They are therefore products displaying 2nd order biotic activity (BA).
Respiration processes have to be specifically controlled (e.g. "dormancy temperatures", and particular temperature, humidity/moisture and ventilation conditions (SC VII) are therefore required, as is intensive ventilation. This is known as temperature-controlled transport. For some plants, the provision of a controlled atmosphere (CA), SC VIII is even more favorable.
Refrigerated containers with a fresh air supply require specific cargo care, and these are known as thermally insulated refrigerated containers with a temperature-controlled atmosphere, i.e. which can be cooled or heated, or CA containers. They are wholly cut off from the external air. The shelf life of fruit and vegetables can sometimes be extended by using a controlled atmosphere, relative to normal refrigerated transport.
Meat and fish also belong to this group, but their biotic activity is only 3rd order (BA 3), so meaning that only particular temperature and humidity/moisture conditions (SC VI) are necessary and they are generally transported in refrigerated containers at subzero temperatures. To prevent weight loss, associated with drying-out of surfaces, high relative humidities are favorable.
Newer refrigerated container units have the technical capability to effect controlled moistening of the cooling air in the plus temperature range. According to practical reports, although these do not solve all the technical problems, the possibility of moistening does exist in principle. At subzero temperatures, this possibility does not exist. The humidity/moisture of the cooling air below freezing depends to a considerable extent on the temperature difference between the cooling air (return air) and the evaporators. How cold an evaporator has to be in order to cool the cooling air to a particular temperature depends in turn on its size (the smaller the evaporator surface, the lower the temperature and vice versa). Furthermore, the humidity/moisture is influenced by the quantity of evaporating, frozen water (sublimation). Since meat and fish are generally loaded in virtually water vapor-tight packaging, the amount of sublimated moisture is very slight. Evaporator sizes are predetermined at the time of construction and there is thus no possibility of influencing humidity/moisture at subzero temperatures. Since, for this reason, it is not always possible to achieve optimum humidity/moisture, it is all the more important that the goods are packaged in water vapor-tight films, for example, in order to prevent weight losses and drying-out.
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