To make a preservation pickle, sheep or goat skins will be given a salt treatment at a concentration of 15° - 20° Baumé to achieve an equilibrium Baumé of approx. 15° after water has been drawn out of the pelts. The pH may be taken down as low as 1.0 - 1.5 with sulphuric acid. This treatment will preserve the pelts for many months or even years but over long periods of time a gradual acid hydrolysis takes place and the fibre will be progressively weakened and there may be problems of fat splitting and fatty acid deposits in the pelts.
The acid hydrolysis of the protein may cause a buffering effect which can raise the pH and encourage mould to take hold and grow resulting in staining and fatty spew problems. As the mould growth increases the pH can rise enough for the stock to putrefy if the salt concentration is not enough.
Stock should be regularly inspected for such problems and if necessary re-pickled, this will also help if any creasing or drying out has occurred. Dried in pickle creases can leave permanent marks in the finished leathers.
To help remove this danger stock which is creased may be re-worked with acid pH range bates such as OROPON DVP or WB and a good antimould / biocide must be used if the pelts are to be stored safely.
So despite the extremes of salt and acid mould can still effect pickled goods. Pickling preserves by the fact that bacterial growth is restricted when the moisture content is reduced and the pH is low. Moulds are not so inhibited by these conditions and even when the pH conditions are very low they can develop on pickled stock.