After pre-treatment of the skin splits or bones ossein, the material is ready for the extraction process.
The physical appearance of the material is virtually unchanged as the skeletal structure is stabilized mainly by hydrogen bonds, which however, are thermolabile.
By treating the material with hot (50°C - 60°C) water, the protein chains, which constitute the collagen molecules, are free to separate from each other and become hydrated.
The hydrated process causes the protein molecules to dissolve in hot water, giving dilute solutions of gelatine.
The extraction treatment is done in 4 or 5 cycles, each resulting in an about 4% gelatine solution. After filtration, concentration and sterilization the liquid will be dried until it contains about 88% gelatine and 12% water.
Gelatine is extracted from the pretreated raw materials continuously or by the repeated addition of warm water in a multistage extraction process. How water is added to the partially extracted material and extraction proceeds anew. This procedure is repeated so many times till the last gelatine residue enters the solution. The result is an approximately 5% solution. The gelatine which has been obtained from the initial extractions at the lowest temperature（approx. 55℃）in the multistage procedure possesses highest gelatinization capacity. In the continuous method, hot water is up to 60 to 85℃ incessantly led into the extractors and gelatine with a constant gel strength is extracted continuously.
