Reduction Plant

At the dock, whole menhaden are unloaded by pumps from the hold of the steamer vessel and conveyed to a continuous-process, steam cooker. Cooking coagulates the protein and releases bound oil and water from the flesh. The mass of solids and liquids is firm enough to withstand high pressurization as it is conveyed through a continuous press. This operation squeezes oil and water containing dissolved and suspended solids from the mass leaving a damp  intermediate known as "press cake," which is conveyed to continuous-process driers. The resulting product (fish scrap) is then milled into meal and treated with an antioxidant that helps the meal maintain its protein and energy qualities during storage and shipment.

The oil and water phase, "press liquor," is pumped through screens and decanters to remove suspended solids that are later returned to the "press cake." The semi-clarified liquor is then separated into the oil and water components by continuous-process centrifuges. The oil undergoes a final centrifuging to remove practically all water and impurities before shipment.

The combination of water and dissolved solids separated from the oil by centrifugation is called "stickwater." At most processing plants, the "stickwater" is partially concentrated in a multi-effect evaporator, and a percentage is returned to the "press cake." When these solids are added to the "press cake" and to the resultant meal, it is then termed "whole" or "full" meal. Some "stickwater" is concentrated to a 50% solids content and brought to a pH of 4.5 to preserve nutritional qualities. This product is called condensed fish solubles.