Eggs turn from liquid to solid upon heating?

13 viewed last edited 3 years ago
Ramanath Parimi
We know that when you heat a liquid, it turns into gas. However, to the contrast, when the insides of an egg are heated, it turns into a solid. How is a semi-solid gel like substance in an egg becomes a solid when heated?
With just a raw egg in your hand, you're holding onto some really exciting chemistry. One of the main components of what you find underneath that shell is protein. The egg white is about 12 percent protein and the egg yolk itself is about 16 percent protein. This means that any alteration to the structure of these proteins will, in turn, significantly alter the structure of the entire egg. All proteins are made up of chains of amino acids, and those egg proteins are no exception. Right now, the proteins are in their normal, or native, state. When a protein is in its native state, the amino acids are folded in a very specific way that gives the protein its shape, and that shape, among other things, gives the protein its properties. A large part of what determines this native shape is how it interacts with water. Parts of the protein are hydrophilic, meaning they love water, and other parts are hydrophobic, meaning they will always avoid water. The water-loving parts will find themselves with the water on the outside of the molecule while the water-avoiding parts hide on the inside of the protein. This interaction, as well as many others, will keep the protein in its shape until you start boiling your eggs. Now put your eggs in the pot, fill the pot with water, turn on the stove, and we can talk about denaturation. Denaturation is what happens when heat is applied to the eggs. Chemically, this is the process by which the chains of amino acids are changed from their original (or native) state. The heat coming from your stove denatures the protein by disrupting some of its bonds that held the molecule into shape. In the case of hard-boiled eggs, the proteins clump together and solidify, causing the egg white and yolk to harden. Here's what happens to the egg whites as they cook. When they're cold, the chain-like protein (albumen) molecules are folded up into little balls. There's a specific way each folds. That arrangement has relatively low entropy. The little balls can roll past each other, so the whole thing is liquid. On heating, the molecules unfold and start flopping around. As you might guess, this has higher entropy. Once unfolded, the molecules get tangled up with each other and flow less easily than when they were little balls. When they then cool down they stay tangled up and really get stuck in a fairly rigid rubbery cluster.
Aditya Reddy