why does raw meat turn brown when cooked?

Answer 1

Heat makes meat brown by setting in motion chemical changes that develop color and flavor compounds not present when the meat is raw. Meat is composed of protein and fat, with 75 percent water interspersed among the protein fibers. Heated protein starts to coagulate (firm) and shrink, squeezing out the liquid and melting some of the intramuscular fat.

Heat also evaporates meat juices, and their residue undergoes color and flavor changes much like meat does. If cooked enough, the residue turns a very dark brown and develops a mellow, sweet flavor as it caramelizes. If you're overly cautious about scorching or burning, the sauce won't get the full, rich color the residue can give

Answer 2

I believe they're called Maillard reactions but its been a while since I picked up my book on food chemistry. Try searching for that.

Answer 3

All the tissues in the meat get denatured.

Answer 4

Due to CO2