Raw hides and skins through the preparatory stages of liming, unhairing and deliming have been transformed into pelts with much of their earlier undesirable components declared enroute. However, they still contain non-leather-making constituents such as degraded proteins, colour pigments grease and lime soap and for further refinements, are subjected to a process called "BATING". The main object of bating is to make the grain surface clean, smooth and fine and give the finished leather its soft, pliable and stretchy feel.

By a trial and error experience of the leather pioneering days, a tanner realised that pelts treated with fermented dung liqour of dog, hen or pigeon gave him relatively cleasn, smooth and fine-grained leather compared to the rough and coarse grain he managed to obtain from non-bated pelts.Although the tanner didnot quite fully understand or grasp the action of the dung, this process remained in use as the only known bate. After persistent efforts at unravelling, J.T.Wood in 1895 found that ammonium salts and enzymes produced by bacteria in the fermented dog dung liqour was actually responsible for the above desired result.

This method continued to be popular with the tanners despite the foul smell of fermented dung bate till 1908, when Dr. OTTO Rohm in Germany researched and patented a preparation containing ammonium chloride and a controlled amount of enzyme extracted from animal pancreas. This synthetic bate he designeted OROPON and introduced it to the tanning world with trmendous success and that too, without the popular prop of commercial jingles or spot ads. OROPON quickly, effectively and completely abolished the old obnoxious bating methods, putting the poor poachers and poultry farmers practically out of business. Tanners gave a respectful burial to their old friend, the dung bate, and their wives gave a sigh of relief. Compared to it , OROPON was a clean product, capable of storage for a long time without deterioration, safe to use, easy to control and above all, free of foul smell.

The following results are obtained from the bating operaation:

1. Further removal of lime and reduction of surface swelling.
2. Loosening of dirt, short hair, grease and lime soap, coloured pigments, etc.
3. Dfissolution of some protein substances principally the interfibrillary matter, leaving the fibers of the leather-making substances in a conducive condition to receive readily the tanning agents and produce the desired fproperties in the finished leather.

 

Starch, proteins and fats taken from an animal's digestive system are complex organic compounds which need to be broken down to simpler materials and made soluble in water by a specific enyme. Enzymes are 'Biological Catalysts' which speed up solubilizing reaction without themselves being used up in the process or becoming a part of the end product.

Protein hydrolysing enzymes-proteolytic enzymes have been evaluated from bacterial, fungal, plant and animal origin for possible use in the leather industry. These enzymes have about the same effect when used as bating materials although they may show minor differences in resistance to temperature changes, activity at different levels of acidity or alkalinity and activation or inactivation by different chemicals. Proteclytic enzymes are specific in their action. Pepsin can hjydrolyes protein only in acid medium(pH 2.0). Trypsin can hydrolyse protein in an alkaline medium(pH 8.5). Delimed pelts are in an alkaline state and therefore, an excellent condition for enzyme action foTrypsin.

For commercial manufacture of bating agents, preserved pancreas is very finely pulped and mixed in required proportion with finely powdered sawdust(wood flour). Sawdust acts as a supporter and distributor of the enzymes between the aqueous medium and the pelt. It also helfps in keeping the fproduct dry and prevents it fron decomposing. This mixture is then combinedwith dry ammonium sulphate or ammonium chloride in various proportions to prepare the different grades of synthetic bates, each having a distinctive enzyme activity. Each grade is recommended for the manufacturre of a specific type of leather.

The best examples are lamb skins for glove leather and hides for sole leather. Glove leather fmainly requires a soft touch with a pleasing grain look and utmost stretch. To accomplish this, the selected grade of enzyme should have a strong activity factor. Sole leather oin the other hand has to be solid and requires very little flexibility. Here the function of a bate is to merely clean the grain. For this purpose the enzyme grade should have a mild activity. Between these two extremes there is a whole spectrum of grades, each selective grade for a specific type of finished leather.

The first synthetic bate of 1908 introduced by Dr.Otto Rohm has through the years grown into a large andsuccessful family of sophisticated, selective and specialised bating agents manufactured by Rohm and Haas Company,under its original tradename of 'ORPON" OroPon bates have through the years of their usage, proved sufficient to cover all types of leather produced in volume in the world.

In practical bating operation the efficiency of the process dependsupon:

1. Temperature of bate liqour
2. Duration of bating
3. Strength of bate liqour
4. pH value of bate liqour