Herring split along the back, brined, sometimes dyed, and cold smoked to produce a product known as a kipper. The brown colouring used is referred to as kipper dye and is usually brown FK. A kipper fillet may be a cold smoked, single fillet of herring (which may then be canned), or a fillet cut from a so-called boneless kipper which used to be produced from a kipper from which the head, belly wall and backbone was removed. A boneless kipper is now usually regarded as a cold smoked, block fillet of herring.