(sometimes gelatine) is derived from collagen (present in skin, connective tissue in meat, and in bones, particularly those of young animals) when it is heated. It is extracted commercially with hot water and acids or alkalis. Transparent and almost colourless, gelatin is sold in dehydrated form, as a powder or in thin fragile sheets. These are used as required, mixed with liquids and flavourings, to ‘set’ savoury aspic, desserts such as jelly and mousse, and stabilize commercially made ice cream and other foods.
Gelatin is important in cookery and the food industry because of this ability to transform large amounts of liquid into an apparently solid substance or gel. The molecules of which it is composed have special properties that make this possible. They are hydrophilic (i.e. attractive to water), and have a long, threadlike structure. When liquid is added to gelatin and the mixture heated, the gelatin first swells, as the water is absorbed, and then dissolves. At this stage the mixture is known as a sol, and contains sufficient energy for the molecules to move freely in the mixture. On cooling, the molecules lose energy and form a mesh in which water is held both by chemical bonds on their surface, and physically in the three-dimensional network. In this form the mixture is known as a gel. If the mixture is beaten whilst viscous but before it is fully set, the gelatin is sufficiently elastic to stretch around and hold air bubbles; the result is then a foam (such as a mousse). Frozen, the mixture becomes ice cream, in which the gelatin also interferes with the formation of large ice crystals, allowing a smoother texture.
Laura Mason has written about several aspects of British food in books including Sugar Plums and Sherbet (1998), Farmhouse Cookery (2005), and Traditional Foods of Britain (1999), which she co-authored with Catherine Brown.
