Flay cuts are knife marks on the flesh side of hides and skins that are caused by careless use of the knife during the removal of the skin from the carcase. Usually, the cuts penetrate well into the corium structure where they result in weak areas.
In severe cases the cuts may extend right through the full thickness of the skin. Even where they do not cut right through the skin, they can invariably be seen from the grain side since the loss of substance means less pressure during certain leather making processes, eg vacuum drying.  For this same reason, flay cuts are also often highlighted by roller coating finishing operations.
Flay cuts are a major, yet unnecessary, contributor to the down-grading of large quantities of leather worldwide.
Flaying
After slaughter the hide needs to be removed from the carcase. This can be done entirely by hand, or with the assistance of mechanical devices. Whichever method is employed, the skin has to be ‘opened’ by a few strategic cuts from the throat, along the chest and belly down to the tail. Radiating cuts are then made from this line along the inside of the legs. If this procedure is not carried out correctly, a devalued misshapen skin can result. In the case of some unusually shaped skins, eg camel or certain reptiles, these opening cuts may be made differently.
Hand flaying
Where mechanised assistance is not available, the rest of the removal process may continue by hand. A sharp bow shaped knife is used to separate the skin from the flesh making sure that as little meat as possible is removed.  In some areas of the skin, pushing the fist between the skin and flesh can assist this separation of skin from meat.
In more primitive conditions, hand flaying may take place with the carcase lying on the ground. But from a hygiene and ease of flaying point of view, it is much better to suspend the carcase, usually by the hind legs. This also encourages proper bleeding. Smaller carcases such as sheep or calf may be raised from the ground in a cradle making it easier for the operative to remove the skin.
Hand flaying is a highly skilled operation and if not performed well results in a significant amount of damage to the hide. To do the job well takes time; up to 15 minutes to flay a cattle hide by hand compared to just a couple of minutes with mechanical flaying. Clearly, in abattoirs that are processing more than a handful of animals per day, this is not effective.
Mechanised flaying
The mechanisation of the flaying process not only speeds up the processing time considerably, but it also significantly improves hide and skin quality. Providing the preparatory cuts are made properly, further use of the knife is kept to a minimum. There are also hygiene benefits since the flaying knife is a major source of infection of the meat as dirt from the hair side is transmitted to the flesh.
After the skin has been opened up, it is clamped to a pulley that pulls the skin off. Usually, this is done from tail to head, but can be performed in the inverted position, pulling from head to tail.  It is thought that there is less contamination of the carcase by using the inverted method as there are more bacteria at the tail end that could fall onto the carcase when the skin is pulled from tail to head.1
Mechanical pulling is, however, not without its own problems; if the skin is not properly opened up or the machine operated too fast, Butcher’s strain (strained grain) may ensue.
Prevention
Like everything else in this world, prevention is better than cure. In fact, in the case of flay cuts, there is no cure; unlike blemishes to the grain surface, they cannot be filled or covered by finish.
If confined to the edges of the hide, they may be trimmed off. But by doing this, there are serious implications with regards to area loss. This major problem can only be overcome by better practices in slaughterhouses. Ideally, this should be in the form of installing mechanical hide pullers or in better training in the art of hand flaying.
But in many parts of the world there are difficulties with power supply and suitably qualified engineers to install and maintain sophisticated hide-pulling machines, not to mention the lack of financial resources to purchase such technology. But the mechanisation of the flaying process need not necessarily be a complicated affair. Pulleys do not necessarily have to be electrically operated. Our own Sam Setter (author of the Limeblast) has designed the Static Flaying Frame that can be used anywhere and claims to reduce flay cuts and holes by up to 60%2. The design is simple enough to be constructed from local materials so it is the ideal solution in many areas where hides and skins are a major source of income and improving quality could bring significant benefits to the local economy.
References
1. Meat Technology Update, CSRIO, December 2000
2. Static Flaying Frame Improves Quality, Leather International 08 October, 2003