Why is a block of cheese solid?

A block of cheese is solid because of a process called curdling. Here's a breakdown:

* Milk's Composition: Milk contains proteins (mainly casein), fats, and water. The casein proteins are tiny spheres that are suspended in the water.

* Adding Rennet: Cheesemaking starts with adding rennet (or a similar enzyme) to the milk. Rennet breaks down a part of the casein protein, causing it to change shape and clump together.

* Curds and Whey: This clumping creates a solid mass called "curds" and a watery liquid called "whey".

* Pressing and Aging: The curds are then pressed to remove more whey, resulting in a solid block of cheese. The cheese is then aged, allowing bacteria and enzymes to break down the proteins and fats, giving it its unique texture and flavor.

In essence, the solid structure of cheese comes from the clumping of casein proteins due to the action of rennet, followed by the removal of whey and further transformation during aging.