Pellets are generally formed between 0.3 – 1.5 mm, though other sizes could be prepared. The benefits of pelleting include enhanced handling characteristics of feeds and improved animal performance. Pelleting increases bulk density and flowability and decreases spillage and wind loss.
The process of producing feed pellets can roughly be described as a plastic molding operation of the extrusion type. Feed ingredients are made up of various compounds such as proteins, acids, sugars, fibers, and minerals.
Those ingredients which are of coarse texture, such as whole grains and other fibrous materials, are ground into a fine meal to facilitate the pelleting and mixing process. Rations containing raw protein produced dramatically stronger pellets than those containing denatured protein. Starch (raw or pregelatinized) had a minimal effect on pellet quality when pelleted with raw protein.
Weighted quantities of each ingredient (either as a batch or continuously) are thoroughly mixed (either in a batch mixer of a continuous flow mixing unit) and then conveyed to a bin above the pellet mill.
The pelleting process starts with a bin in which the mixture of mash is stored. The mash was fed through the hopper and is carried through the barrel length by the screw conveyor. Between the screw conveyor and the die is a space which allows for caking of the feed. The feed then passes through the die where the cylindrical shape of the pellets is formed.
The formation of the pellet actually occurs at the “nip” between the rolls and the die. All other activities associated with the operation such as conditioning, cooling, etc., really support and augment the action at that point in the system.
The hot, extruded mash (pellets) is held for three to six minutes while being cooled and dried by a flow of air.
The pelleting die is required to restrict the flow of feed material and provide the cylindrical shape of the pellet. The die plate had a thickness of 5 mm. The effective diameter of the die plate was 80 mm.
From the cooler, the product flows through or around a pair of crumble rolls. If we wish to produce a relatively fine product, about the size of cracked corn, then the pellets are passed between the crumble rolls to be crushed (cracked) to a smaller size.
Food pelleting
