When we cook an egg why does the eggwhite solidify while yolk is liquid?

That's a great question! Here's the breakdown of why egg whites solidify and yolks stay liquid when cooked:

The Science of Egg Proteins:

* Egg White: Egg whites are primarily made up of water and a protein called albumin. Albumin is a long, folded chain of amino acids.

* Egg Yolk: Egg yolks are richer in fat and contain different proteins, including livetin and vitellin.

The Impact of Heat:

* Egg White Solidification: When heated, the albumin molecules in the egg white unravel and unfold. These unfolded proteins then bond to each other, creating a network of interconnected strands. This network traps water, giving the egg white its solid, firm texture.

* Egg Yolk Liquidity: The fat and proteins in the yolk also change when heated, but they don't form the same kind of network as the albumin in the white. The yolk proteins become thicker, but they retain their liquid form. The yolk's high fat content also helps keep it liquid.

Additional Factors:

* Temperature: The temperature at which an egg is cooked significantly affects how it sets. Higher temperatures cause faster protein unfolding and solidification.

* Time: The longer an egg is cooked, the more the proteins solidify.

* Acidity: Adding vinegar or lemon juice to boiling water can make egg whites set more quickly. This is because acid disrupts the protein structure, making them easier to unfold.

In a nutshell: The difference in protein structure and composition between egg whites and yolks, coupled with the effects of heat, explain why one solidifies while the other remains liquid when cooked.