Gelatin is widely used in the food industry, pharmaceutical industry, and other fields, and is an indispensable product in our daily lives. In this article, I will introduce one of the most common gelatin production methods—the alkaline method. This method is widely used both domestically and internationally, and has the advantages of simple processing and low cost. This process consists of nine steps: preparation, pre-soaking, degreasing, re-soaking, washing, boiling, concentration, bleaching, and drying.
I. Sorting
Different types of animal hides are sorted, washed, and placed in a container. Water is added to cover the raw materials. While continuously stirring, 6N hydrochloric acid is added to the water to adjust the pH to 2.5-3.5. Initially, acid is added every half hour for adjustment; after 3 hours, acid is added once an hour for adjustment; after 8 hours, no further acid adjustment is needed. This process takes 12-16 hours to complete. Finally, the waste acid water is drained, and the material is rinsed with clean water and thoroughly stirred. The water should be changed at least 8 times, and this process should be completed within 8-12 hours.
II. Pre-soaking
The sorted raw materials are soaked in 1% lime water for 1-2 days to loosen and open the collagen fibers, making them easier to cut. Then, they are removed and cut into small pieces for later use.
III. Degreasing
The block-shaped raw materials are continuously fed into a hydraulic degreasing machine with water. The machine’s mechanical action and water pressure remove fat and impurities.
IV. Soaking
The degreased raw materials are soaked in 2%-4% lime water with a specific gravity of 1.015-1.035 in a cement tank, wooden barrel, or vat. The concentration of the lime water can be adjusted flexibly according to the temperature; a lower concentration is used at higher temperatures, and a higher concentration at lower temperatures. The ratio of raw materials to water should be 1:3, the pH should be 12-12.5, and the temperature should ideally be 15℃. Soaking takes 15 days.
V. Washing
The soaked raw materials are thoroughly washed with clean water while continuously stirring. For the first 5 hours, change the water every half hour, and then change the water every hour. The ratio of raw materials to water should be no less than 1:5. The entire cleaning process takes approximately 12-16 hours.
VI. Gelatin Extraction
Add hot water to the gelatin extraction pot, and then add the cleaned raw materials, ensuring they do not clump together. Then, slowly raise the temperature to 50-65℃, ensuring the water completely covers the raw materials. After 3-8 hours, remove the gelatin solution, add more hot water to the pot, increasing the temperature by 5-10℃, and continue the extraction process. Repeat this process several times, gradually increasing the temperature, and the last extraction can be done at the boiling point. After the gelatin extraction is complete, filter the resulting dilute gelatin solution at 60℃ using filter cotton, activated carbon, or diatomaceous earth as filter aids, and a plate and frame filter press. Once the gelatin solution is clarified, use a centrifuge to separate and remove oils and other impurities. If there is oil floating on the surface of the dilute gelatin solution from pigskin gelatin extraction, it should be removed.
VII. Concentration
The dilute gelatin solution separated by the centrifuge is concentrated under reduced pressure. The initial temperature is controlled at 65-70℃, and later the temperature should be lowered to 60-65℃. The degree of concentration should be controlled according to the quality of the gelatin solution and the conditions of the drying equipment. Using hot and cold air drying, the gelatin solution at 50℃ can be concentrated to a specific gravity of 1.050-1.080, with a gelatin content of 23%-33%.
VIII. Bleaching
Hydrogen peroxide or sulfurous acid has bleaching and antiseptic effects. After obtaining the concentrated gelatin solution, add hydrogen peroxide or sulfurous acid and other preservatives while the solution is still hot. Then, pour it into a metal basin or mold to cool until it completely gels and forms a gelatinous mass.
IX. Drying
Cut the gelatinous mass into appropriately sized thin slices or pieces, and dry until the moisture content is 10%-12%, then pulverize it to make the finished product. The drying process can be divided into two stages: in the first stage, water evaporates quickly, so the air volume should be larger and the temperature lower to prevent it from turning into a liquid; in the second stage, a film has formed on the surface of the gelatinous mass, and water evaporates slowly, so the air volume can be smaller and the temperature should be higher. The dried and crushed product is then ready for use or sale.