The processing of raw material for fishmeal and fish oil production essentially follows a cooking, pressing, extraction and drying cycle that separates out the fishmeal and fish oil, producing only steam as a byproduct. In effect, a product that incorporates all of the raw material other than a major fraction of the water it contained is produced. Processing follows strict quality management procedures to ensure that product parameters are within recognized ranges for nutrients and contaminants. The process is highly technical in order to retain the nutrient qualities that are found in the raw material as far as possible, and ensure that these are transferred to the end products of fishmeal and fish oil.
Fish is first typically cooked to coagulate protein and allow some oil to be released, using a temperature of 85°C to 90°C. In addition, micro-organisms are killed by this process (see diagram). Clean conveyors, holds and storage pits, short storage time and reduced temperatures minimize micro-organisms and the spoilage they may cause. The lower temperatures also reduce fish enzyme activity (autolysis), another form of spoilage. Cooked fish then passes into a screw press where liquor is pressed out and the solids (press-cake) go to the drier.
The liquor is decanted to remove further solids. It is then centrifuged to spin off oil and separate out an aqueous phase (stickwater). The stickwater passes through evaporators to reduce its volume (concentrate). This concentrated liquor (called stickwater because it tends to be viscous and sticky) is returned to the press cake entering the drier. A typical drier contains coils through which super-heated steam passes. These coils raise the temperature to 90°C (controlled by flow rate etc.) for drying to around 10% moisture after cooling. Low temperature driers such as indirect hot-air or vacuum driers, operate at lower temperatures.
Fish oil may go on to be purified to remove solid impurities; special filters can be used where appropriate to remove some fat-soluble impurities. More sophisticated refining is used to produce a clear odorless liquid for pharmaceutical/nutraceutical uses e.g. capsules.