Putrefaction

 The proteolytic enzymes which they produce can cause untold damage to the hide or skin. Some typical problems in leather which can be caused by putrefaction are: * Grain damage * Weakness * Looseness * Staining * Chrome soaps * Spue * Uneven dyeing In addition, putrefaction can weaken the delicate grain surface and make it more susceptible to the rigours of normal leather production, leading to chemical damage and physical abrasion. The cause Soon after flaying the hide is moist, warm and full of protein - an ideal breeding ground for bacteria! The longer these conditions prevail, the more putrefactive damage will occur. Some common causes of putrefaction in hides and skins are: 1) A delay between flaying and curing/processing 2) Insufficient salting or brining 3) Poor penetration of the salt or brine due to heavy fat/flesh deposits 4) Insufficient draining of the salted or brined hide or skin allowing liquors to pool and reduce salt concentrations 5) Poor storage conditions of the raw salted hide or skin, eg exposed to the elements allowing salt to be washed off or excessively warm conditions 6) Prolonged storage, particularly under warm conditions 7) Soaking the raw hides or skins without sufficient biocide protection Sometimes, even when hides have been well salted or brined, bacteria can still grow. These are a particular type of bacteria which are halophilic (salt loving) and are commonly coloured red or purple; affected hides are said to have 'red heat'. Under normal storage conditions for raw hides or skins, red and purple heat bacteria take a relatively long time to grow; around two to three months. Therefore, their presence is an indication that the hides or skins have been in storage for some time. However, at higher temperatures (30-40ºC), growth will be more rapid. The warm, humid conditions favoured by red heat bacteria are also favoured by other non coloured spoilage bacteria, so if salt levels are not high enough, putrefactive bacteria may also be present. It was once thought that red heat bacteria caused no harm to the hide, but it is now known that some types of bacteria do produce proteolytic enzymes which are capable of damaging collagen. Although red heat bacteria are aerobic and, therefore, only grow on the surface of the hide or skin, the enzymes that they produce are mobile and can penetrate further into the skin structure. Any proteolytic enzymes which may be produced by purple heat are even more likely to cause damage because they can proliferate within the hide structure. Prevention Rapid and appropriate curing is a key issue in the prevention of putrefaction: the hide should be cooled immediately after flaying in order to dissipate any remaining body heat, and kept cool until the hide is salted. As soon as practicable, the hide should be treated with clean salt, in a quantity equivalent to no less than 35% of the green hide weight. Mechanised agitation will produce a more rapid absorption of salt, while piling will call for a minimum of seven days in salt, and preferably 14 days, to effect the level of saturation required. When salt penetration is adequate, the remaining salt should be 'biffed' off and a sprinkling of fresh salt applied before the hides are prepared for shipment in accordance with market practice. Once at the tannery, the hides should be stored appropriately. Cool dry storage conditions for hides help maintain a good standard of preservation. Storage in the open, where hides are not covered, can cause the hides to heat up if in direct sunlight, encouraging bacterial activity and drying out. Thermal damage may also occur to hides, particularly if stored in direct sunlight under clear polythene. Under humid atmospheric conditions, salt can absorb moisture from the atmosphere which results in a reduced salt content at the surface of the hide. Salt can also be lost from the hides by drainage of this moisture. Leaching out of salt can also occur where hides are left open to rain.