Gels

Abstract

Cooked egg white, frankfurters, yogurt, jellies, and gelatin desserts are traditional food products that are gels. All start as some liquid mixture of ingredients in water which solidify as a result of processing. Hard-boiled eggs are one of the simplest; by placing whole eggs in boiling water for 5 min, you cause the liquid suspension of proteins in the egg albumen to denature, aggregate, and form a gel network. Changing the cooking time allows some control of the texture of the product. Another interesting egg product is the “thousand-year-old egg.” Strong black tea, salt, lime, and wood ash are combined into a paste and buried in soil. After 100 days in a cool dark place, the egg white forms a translucent gel. Different processing conditions convert the same protein into gels with different properties. Other food ingredients form more complex gels, for example, in making cheddar cheese, the initial process involves forming the liquid milk into a soft-solid curd by starter cultures lowering the pH, and by the enzymatic action of chymosin. The gel is weak and fractures with minimal deformation.