I have been hesitating whether to write or not an introductory post about eggs. The reason? It's a well-discussed topic: there are countless books, articles and posts about that! Do we really need one more post about eggs? Well, given what I am going to discuss in the next few posts, yes...you have to swallow another article about that, it's propeadeutical :)
Eggs are an intriguing food. Besides the possibility to eat them tout court, they possess an unique versatility. Eggs are part of countless preparations: mayo, custards, basic pastry dough as sponge cake, shortcrust and so on. Can we imagine all these recipes without eggs? Not really, right? It is not a case that eggs are the most studied food by scientists and chef, and we can find a wide literature about that. Below, you can see a graphical representation of an egg sectioned:
This is a simplified drawing, the structure of an egg is actually much more complex. When I was in High School, I was surprised to learn that bird eggs are single cells, better known as oocytes. Is that obvious? Well, maybe I never made 2+2...More precisely, only the yolk represents the oocyte, while the rest (egg white and shell) forms in the oviduct of the hen and function as supportive and protective material.
The biology of eggs is rather complex and it is beyond the scope of this post. What I would like to discuss is the function of eggs in the kitchen. I heard my grandma commenting: "How can you make a cake without eggs?? Is it not going to fall apart?" Now, my grandma worked in a pastry shop for most of her life, as it was the family business, so she knew about that. But why do we need eggs in our recipes? Was my grandma right about that?
Eggs have emulsifying properties, therefore, as explained in the former post, they act as a bridge between fatty (hydrophobic=repelling water) and watery stuff (hydrophilic=affine to water). So, my grandma was right: eggs act as a glue in your dough. But there is more: eggs keep together mayo and custards for the same reason.
What are the emulsifying compounds in eggs and where you can find them? In the figure below, you can observe that all the fats and most of the proteins are in the yolk, while the egg white contains mostly water, proteins and a small percentage of salts:
Lecithin, contained in the yolk, and proteins are the main emulsifiers. Both class of molecules contain hydrophobic and hydrophilic portions that allow bridging fat and water. In the former post, I have already shown how lecithin (a mix of phospholipids, actually) works. And proteins? How they can act as emulsifiers? We will see that in the next post, where we will also go through the first scientific recipe :)
Leonardo di Carlo, “Tradizione in evoluzione”, 422-423, Chirotti Editori