The wet refiner function is to remove the impurities such as skin, pin bones, scales and connective tissues from a slurry of fish meat and water by filtration through a screen. The slurry is pumped into the receiving side of wet refiner and thrown onto the cylindrical screen by rotating blades. The meat is carried with the water through the screen usually with 0.8 to 1.2 mm holes while the impurities are retained by the screen. The blades have a helix shape that carries the impurities to the discharge at the exit side of the refiner.
One advantage of the wet refiner is to separate cleaned impurities and allow recovery of nearly 100% of the meat which is carried by the water phase working as a lubricant and protecting the protein from physical denaturation.
The slurry feeding the wet refiner may contain up to 40% solids mixed with water and the dehydration is usually done by decanter. This combination of wet refiner and decanter is used to process surimi from pelagic fish like sardine or horse mackerel which contain too much fat and cannot be dewatered by screw press.
Wet refiners are also used to recover the meat that remains in the waste material of Japanese refiners and may represent 30 to 70% of the waste. A combination of nylon mesh screen and small screw press can also be used for filtration and dewatering of this recovery meat from Japanese refiner waste to minimize the investment cost but the yield is usually lower than using a decanter.
The wet refiner is equipped with a spray system that can be used to help the blades push the impurities through the wet refiner and prevent vibrations of the machine that occur when impurities are not properly carried out to the discharge.