Fish meal, or fishmeal, is a commercial product made from fish and the bones and offal from processed fish. It is a brown powder or cake obtained by drying the fish or fish trimmings, often after cooking, and then grinding it. If it is a fatty fish it is also pressed to extract most of the fish oil.
The use of fish by-products is not a new idea; it has been used in previous times to feed poultry, pigs and other farmed fish.
Fishmeal can be made from almost any type of seafood but is generally manufactured from wild-caught, small marine fish that contain a high percentage of bones and oil, and is usually deemed not suitable for direct human consumption. The fish caught for fishmeal purposes solely are termed “industrial”. Other sources of fishmeal is from by-catch of other fisheries and by-products of trimmings made during processing (fish waste or offal) of various seafood products destined for direct human consumption. Virtually any fish or shellfish in the sea can be used to make fishmeal, although there may be a few rare unexploited species which would produce a poisonous meal.
Fishmeal is made by either cooking, pressing, drying and grinding of fish or fish waste to which no other matter has been added. It is a solid product from which most of the water is removed and some or all of the oil is removed. Four or five tonnes of fish are needed to manufacture one tonne of dry fishmeal.
There are several ways of making fishmeal from raw fish; the simplest way is to let the fish dry out in the sun. This method is still used in some parts of the world where processing plants are not available, nevertheless the end product is poor in comparison with ones made by modern methods. Nowadays all industrial fish meal is made by the following processes:
Cooking A commercial cooker is a long steam jacketed cylinder through which the fish are moved by a screw conveyor. This is a critical stage in preparing the fishmeal, as incomplete cooking means that the liquor from the fish cannot be pressed out satisfactorily and overcooking makes the material too soft for pressing. No drying occurs in the cooking stage.
Pressing A perforated tube with increasing pressure is used for this process. This stage involves removing some of the oil and water from the material and the solid is known as Press cake. The water content in pressing is reduced from 70% to about 50% and oil is reduced to 4%.
Drying It is important to get this stage of the process right. If the meal is under-dried, moulds or bacteria may grow. If it is over-dried, scorching may occur and this reduces the nutritional value of the meal.
Two main types of dryer: Direct and Indirect
Direct Very hot air at a temperature of 500°C is passed over the material as it is tumbled rapidly in a cylindrical drum. This is the quicker method, but heat damage is much more likely if the process is not carefully controlled.
Indirect Cylinder containing steam heated discs which also tumble the meal.
Grinding This is the last step in processing which involves the breakdown of any lumps or particles of bone are involved in this stage.