A dry-aged ribeye loses water but often feels more tender. What softened it first?

Answer: Postmortem proteolysis

Slow salt-like brining — Not quite. Brining tenderizes by moving salt and water, but dry-aged beef is not being slowly salted from the outside. The early tenderness gain comes from enzymes already inside the muscle cutting key structural proteins after slaughter. The useful twist is that wet-aged beef gets much of this same tenderizing in a sealed bag, so dry aging's special value is more about flavor and yield sacrifice.

Postmortem proteolysis ✓ — Right. Postmortem proteolysis means the meat's own enzymes, especially calpain systems, snip structural proteins that hold muscle fibers in a firm lattice. USDA tenderness work describes this breakdown as the reason aging tenderizes meat, and the dry-aging review notes that the largest tenderness gains arrive in roughly the first 7-14 days. Water loss can intensify flavor, but enzymes do the first softening.

Fat melting through meat — Not quite. Marbling can make cooked steak seem juicier because melted fat lubricates the bite, but fat is not tunneling through the muscle and dissolving toughness. The early softening is biochemical: internal enzymes weaken myofibrillar links. A lean cut can still tenderize during aging, while a fatty cut can still be tough if those structural proteins are not broken down enough.