Fishmeal and fish oil are produced by a continuous and carefully controlled process which involves cooking, pressing, drying and milling of fresh, raw fish. Yields of fishmeal and fish oil can vary between fish species and even from season to season, but typically around 17 – 22% fishmeal and 5 –15% fish oil will be obtained by processing. The following summary provides a step by step guide to the production process.
1. Intake – Raw fish is sampled and analysed on intake to check for freshness and expected yield of meal and oil.
2. Cooking - The raw fish is conveyed through a steam heated continuous cooker, where it is heated to 90°C-95°C. This sterilizes the fish, coagulates the proteins and disrupts the cell membranes to facilitate the separation of the solubles and the oil from the dry matter.
3. Press - The cooked raw material is fed to a screw press where much of the liquid is squeezed out to form a presscake which is conveyed to the drier.
4. Separator – The press liquid contains water and most of the oil from the fish, as well as dissolved proteins, salts and fine particles. These particles, sometimes called sludge, are removed in a decanter and transported to the drier to be mixed in with the presscake. The liquid from the decanter is fed to separators where the oil is removed and can subsequently be stored in large tanks for export.
5. Evaporator - The water phase from the separators is fed to the evaporators where it is gently concentrated before being blended with the presscake during the drying stage.
6. Drier - The water in the press cake, sludge and concentrate is removed by rapid air drying after which the fishmeal is cooled, milled and stored for export.
This method of processing is necessary to obtain marketable products which can be easily stored, transported and utilized.
Click here for a diagram showing the production process (100kb)
Click here for a diagram showing the drying process (47 kb)