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close this bookSmall-Scale Processing of Fish (ILO - WEP, 1982, 140 p.)
close this folderIII. DRYING
View the documentIII.1. Basic principles
View the documentIII.2. Natural drying
View the documentIII.3. Artificial drying
View the documentIII.4. Solar drying

III.2. Natural drying

Natural or air drying uses the combined action of the sun and wind without the help of equipment. It is important to dry the fish quickly before they spoil, and that all surfaces of the fish be open to the drying action of the wind. Where only a few large fish are to be dried, this may be done by hanging the fish up. Split fish may be hung on hooks, by tying them up with string, or by tying the fish in pairs by the tail and hanging them across a pole or line.

Large quantities of fish should be dried on racks. Suitable materials for drying racks include chicken wire, old fishing nets, and thin rods or poles such as reeds or sections of bamboo. The surface of the racks should be at a height of about 1 m from the ground and should slop if split large fish are to be dried. A flat surface is preferred for drying small intact fish. Designs for fixed drying racks are shown in Figure II.2. These racks can be easily covered with plastic sheets to protect the drying fish from the rain. Where large quantities of very small fish are to be dried, a netting rack may be impractical. Suitable drying surfaces may be made instead, with raised floors of wood, concrete, bamboo strip or, where none of these materials are available, well compacted clay.

In the tropics, the air is relatively dry during the day (unless it rains) and relatively wet during the night. From sunrise until about midday, the air becomes gradually drier and, becoming wet again from midday to nightfall. The drying rate - especially in the case of salted fish - is therefore the highest from about 8 or 9 o’clock in the morning to 4 or 5 o’clock in the afternoon. Fish which have been set to dry during the day should be collected, and stored overnight to avoid them becoming wet by dew or rain. The fish in storage should be piled in a similar manner as for dry salting although no further salt should be added. Wooden boards, weighted with clean rocks or other suitable material, should be placed on the pile of fish in order to flatten them and give them a better appearance. This use of pressure will also speed up the process by which water moves from the inside of the fish to the outside so that they will dry more rapidly when set out the following morning.

Figure II.2. Fixed drying racks with flat and slanding tops