Fish products and Byproducts Technology

Unit 9 - Fish meal and fish oil

9.8.1.a. Wet Reduction Process
The processing techniques involved in commercial production of edible fats and oils vary according to the type of raw material. Fish reduction to produce oil and fishmeal, generally employs the same principles, techniques and equipment common to the production of the other edible fats and oils. In general, fish are processed by the wet reduction method in which the principal operations are cooking, pressing, separation of the oil and water with recovery of oil, and drying of the residual protein material. Continuous processing from the time the fish are landed optimizes efficiency and maximizes product quality.
The wet rendering process is used in the majority of the factories that produce fish oil worldwide. This process is universal, i.e. factories all over the world both on land and on ships employ it with slight differences in equipment type, but the major steps of cooking, pressing, separating, and drying are always present. These steps are as follows:
Cooking
Steam cooking ruptures the fat cells, coagulates the protein and releases the oil
Dewatering / Pre-pressing
The cooked fish mass is screened to separate free liquid from the solids
Pressing
Pressing mechanically expresses the free liquid from the solids producing a press liquor (oil and water) and a press cake (semi-moist meat and bones). Some factories have used tri-canters instead of presses to separate solids, oil and water.
Press liquor Separation
This is 3 step process; decanters separate fine solids from the liquid fraction, separators split the liquid fraction into fish oil and water (stick water), and polishing water washes the crude fish oil before it is pumped to storage.
Evaporation
Stick water contains about 8% solids which are concentrated in multiple effect or waste heat evaporators to about 40-50% solids. If the factory uses steam dryers then the waste heat from the dryer can be used to heat and evaporate the stick water.
Drying
The drying process is generally done in 2 stages. The solids from the decanter separation and the press cake are mixed and partially dried. The partially dried fishmeal is then mixed with the concentrated stick water and the drying is completed to about 10% moisture. Factories use steam and indirect hot air dryers but older factories still use the old direct fired hot air dryers.
Grinding
Grinding reduces the particle size of the fishmeal
Cooling and Stabilization
The fishmeal is cooled and antioxidant is added. Generally ethoxyquin is the antioxidant of choice but for certain markets natural antioxidants based on tocopherols are used.
Packaging
The fishmeal is packaged in 50 kg bags or 1000 kg totes. The fishmeal can also be stored in bulk piles or in silos.
Carbon Treatment (Optional for Fish Oil)
If the crude fish oil is destined for the Omega-3, animal feed, aquaculture or pet food market and if analyses indicate the presence of dioxins, furans and or poly-aromatic hydrocarbons (PAH), it can be treated with activated carbon to reduce the levels of these compounds.