A world of gels
When we talk about gels, we tend to think about the ones for hair styling :) However, gels are widely abundant in the kitchen! Let's just think about puddings, fruit jelly, but also savory preparations as quiches, all examples of gels.
From the physical-chemistry point of view, gels are colloids (toh! :)). More precisely, gels are solids with water trapped within. In the recipes, the solid net is usually made of proteins, as collagen. However, also egg proteins can form gels, to do not mention pectin (complex sugars contained in fruits) that are widely used to prepare jelly fruits.
Let's know see how a gel forms. For example, let's take gelatin that is basically collagen, a protein whose polypeptides are associated into a triple helix. Collagen is very abundant in animal tissues from which it is extracted. Gelatin can be purchased as foils or powder. Both must be re-hydrated before use. Then, gelatin must be dissolved in hot water before adding it to the mixture to jellify. The heat denatures the triple helix and the polypeptide chains are now free to move.
Graphical representation of the collagen triple helix.
During the cooling down, the chains associate in a net that traps water within. Et voila', your gel is ready :)
Gelatin based gels are relatively easy to make. On the other hands, pectin gels are quite sensitive to pH that makes their preparation very delicate. We will see different types of gels in the next posts. But this Thursday, I will provide you with the usual recipe :)
Graphical representation of the gel net. The blue balls are water molecules trapped into the net.
References
S. L. Kittsley, Phisical Chemistry, 222-223, Barnes & Noble