Gelatin (from French gÃ©latine) is a translucent, colorless, odorless, brittle, nearly tasteless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar way are called gelatinous. Gelatin is an irreversibly hydrolyzed form of collagen, and is classified as a foodstuff, with E number E441. It is found in some "gummy" candies as well as other products such as marshmallows, Jell-O, and some low-fat yogurt. Some dietary or religious customs forbid the use of gelatin from certain animal sources, and medical issues may limit or prevent its consumption by certain people. Gelatin is a protein produced by partial hydrolysis of collagen extracted from the bones, connective tissues, organs and some intestines of animals such as domesticated cattle, pigs, and horses. The natural molecular bonds between individual collagen strands are broken down into a form that rearranges more easily. Gelatin melts to a liquid when heated and solidifies when cooled again. Together with water, it forms a semi-solid colloid gel. Gelatin forms a solution of high viscosity in water, which sets to a gel on cooling, and its chemical composition is, in many respects, closely similar to that of its parent collagen.  Gelatin solutions show viscoelastic flow and streaming birefringence. If gelatin is put into contact with cold water, some of the material dissolves. The solubility of the gelatin is determined by the method of manufacture. Typically, gelatin can be dispersed in a relatively concentrated acid. Such dispersions are stable for 10â€“15 days with little or no chemical changes and are suitable for coating purposes or for extrusion into a precipitating bath. Gelatin is also soluble in most polar solvents. Gelatin gels exist over only a small temperature range, the upper limit being the melting point of the gel, which depends on gelatin grade and concentration and the lower limit, the ice point at which ice crystallizes. The mechanical properties are very sensitive to temperature variations, previous thermal history of the gel, and time. The viscosity of the gelatin/water mixture increases with concentration and when kept cool (Ëœ 4 Â°C). The worldwide production amount of gelatin is about 300,000 tons per year (roughly 600 million lb) . On a commercial scale, gelatin is made from by-products of the meat and leather industry. Recently, fish by-products have also been considered because they eliminate some of the religious obstacles surrounding gelatin consumption . Gelatin is derived mainly from pork skins, pork and cattle bones, or split cattle hides; contrary to popular belief, horns and hooves are not used. The raw materials are prepared by different curing, acid, and alkali processes which are employied to extract the dried collagen hydrolysate. These processes  may take up to several weeks, and differences in such processes have great effects on the properties of the final gelatin products . Gelatin can also be prepared at home. Boiling certain cartilaginous cuts of meat or bones will result in gelatin being dissolved into the water. Depending on the concentration, the resulting broth, when cooled, will naturally form a jelly or gel. This process, for instance, may be used for the pot-au-feu dish. While there are many processes whereby collagen can be converted to gelatin, they all have several factors in common. The intermolecular and intramolecular bonds which stabilize insoluble collagen rendering it insoluble must be broken, and the hydrogen bonds which stabilize the collagen helix must also be broken . The manufacturing processes of gelatin consists of three main stages: Pretreatments to make the raw materials ready for the main extraction step and to remove impurities which may have negative effects on physicochemical properties of the final gelatin product, The main extraction step, which is usually done with hot water or dilute acid solutions as a multistage extraction to hydrolyze collagen into gelatin, and finally, The refining and recovering treatments including filtration, clarification, evaporation, sterilization, drying, rutting, grinding, and sifting to remove the water from the gelatin solution, to blend the gelatin extracted, and to obtain dried, blended and ground final gelatin.