Pretreatment of Raw Materials In Gelatine Process
Acid Treatment
Normally the skins and hide splits are pretreated by acid pulping. Unlike cattle, skins are relatively young when they are slaughtered. As the tissues of the skin are not yet cross-linked to a great extent, no intensive and time-consuming pretreatment with alkali is required. An acid treatment over one day is all it takes to make the collagen it contains soluble in hot water; this is conditional for the extraction process. Subsequent to acid treatment the excessive acid is partially neutralized and the salts are washed out by exchanging the water several times.
Gelatine can also be obtained from ossein by acid treatment – the concentration of the acid and the exposure time must be adjusted accordingly. Gelatine produced this way is referred to as Type A gelatine (A = acid).
Alkaline Treatment
In this method, ossein or hide split are treated with calcium hydroxide, which is substituted a number of times, for a period of up to three months. In this treatment step, collagen bonds are partially destroyed while non-collagenous proteins and adhering matter are also removed. When producing gelatine from hide split, the raw material can be alternatively treated with diluted sodium hydroxide instead of calcium hydroxide as it produces the same results. After this processing step, called
“liming”, the pretreated raw material is washed once again, neutralized by the addition of acid, and freed from the arising salts by another intensive washing step.
The gelatine thus pretreated with alkali is referred to as Type B gelatine (B = basic).