Q. Can you explain Gels ?

Gels may be formed by the proteins of egg or flour in products like souffles, puddings, custards, batters and doughs. When the protein particles are dispersed in water, the solution like mixture results in the formation of a sol. When a sol assumes a rigid form, it is referred to as a gel.

The change of sol to gel form may be brought about by a change of concentration of the dispersed phase, a change in temperature, or a change in the hydrogen-ion concentration or electrolyte content.

Gel formation takes place when the dispersed phase develops into a network structure that holds the liquid phase in its meshes. In some gels, the framework can be broken by agitation or heat. When this happens, the gel structure reverts back to the sol form. However gels formed as in case of baked custards are of non-reversible types.

When only a part of sol changes to the gel form, the process is known as flocculation. An example of this process can be seen in heated milk when a precipitate coats the bottom of the pan.

Syneresis is the process when the gel on shrinkage results in the loss of liquid. This process was first observed in 1861 by T. Graham, who described the process as an exudation of small amounts of liquid on standing because of a slight contraction of the gel. Although no net volume change occurs in the gel, syneresis cannot be described as a reversible process.