The rollers continuously press layers of mash inside the die hole, by which the pellet is actually built up. The application of mechanical energy by rollers on a die results in
pressure and friction in the die. The extent of compression depends on the height of the layer and the gap distance betweenthe die and the roller. Die holes can differ in their length to diameter ratio, influencing the amount of shear which thefeed mash receives. After leaving the die, pellets are usually cooled by air flow or using a conveyer belt (Thomas et al.,1997).