Eggs are without a doubt the most common thickener used in the pastry kitchen. Long, tangly proteins are the source of their thickening power, which can bring the water flow around them to pretty much a complete stop. Though egg proteins naturally occur in small clumps, they can be convinced to un-clump with the application of a little heat or with some agitation. Once they’re unfolded they can be further convinced to bond at which point all manner of textures are possible depending on the degree of protein coagulation: a thick liquid crème Anglaise, a semi-flowing pastry cream, a fully gelled crème brûlée or a crisp baked meringue. All the cook must guard against is over-heating or over-agitating those egg proteins which causes them to completely coagulate, squeeze out the moisture that’s between them and form tough curds.
One of the most fascinating things about egg proteins is how manipulable their coagulation temperature is. An egg white starts to gel at a very low temperature indeed: 145 degrees Fahrenheit. It becomes firm at 150 and solid by 180. However by introducing other ingredients — such as dairy, sugar, fat and flour — we can raise all those coagulation points as high as several hundred degrees. Amazing, really. There’s so much that can be said about eggs. For now I guess I’ll keep it short!