Abattoir Practices and Animal Products Technology

MANUFACTURE OF GELATINE AND GLUE

• Principle
  • Gelatine is produced by the action of hot or boiling water on collagen or ossein by the process of hydrolysis
• Procedure
  • Washing
    • Defatted and uniformly crushed bones to a size of 1-2 cm are washed with water.
    • Similarly, the glue stock is washed and soaked with water.
    • It is decreased by prolonged exposure to sun or brined or limed (saturated Ca(OH)₂ solution, 10% by weight) for several weeks to remove the non\collagenous material and fat.
  • Demineralization
    • Then it is washed and is demineralized by soaking in 4-10% HCl for 1-2 days.
    • It is washed with water to yield a clean, soft stock or ossein.
  • Extraction or cooking
    • 60°C (140°F) highest quality glue
    • It is done by controlled hydrolysis to recover different grades of gelatine.
    • Extraction is done in steam-jacketed pans and it takes place in several runs of 3-5 hours at successively higher temperatures.
    • No direct flame is used.
    • The heat treatment yields glue as follows
      • At At 65.5°C (150°F) medium quality glue
      • At 80°C (176°F) low quality glue
      • At boiling point the quality is the lowest.
    • Residue is pressed and dried for use as livestock feed or fertilizer.
  • Filtration
    • The liquor or soup is drawn off from each cooking by pressure filtered to increase clarity.
  • Concentration
    • The liquid extracts are vacuum evaporated to yield gelatine of 30-40% concentration.
  • Drying
    • The concentrated gelatine is spread on a thin sheet of a large drum, which is heated by steam (spray drying).
    • Then the gelatine cut and removed in few minutes with the help of a knife.