How does marinating actually change meat before cooking?

Marinating changes meat through a few physical and chemical processes. Acidic ingredients like vinegar, citrus juice, or wine begin to denature surface proteins, which slightly softens the outer texture. Salt draws moisture out initially through osmosis, then pulls it back in along with flavor compounds, seasoning the meat more deeply than surface application alone. This brining effect also helps the meat retain moisture during cooking. However, marinades penetrate only a few millimeters into the flesh even after many hours, so most flavor impact stays near the surface. Enzymes in ingredients like papaya or pineapple can break down muscle fibers more aggressively, genuinely tenderizing the meat, but over-marinating with these causes a mushy texture.