Doneness
The degree to which a steak has been cooked, defined by internal temperature and the resulting protein denaturation.
Doneness describes the degree of cooking in a steak, measured by the internal temperature at the geometric center. Each doneness level corresponds to a specific range of protein denaturation, moisture retention, and color change.
Standard doneness levels: - Blue/Very Rare: 115–120°F — cool, deep red center, very soft - Rare: 120–125°F — cool red center, slight resistance - Medium-Rare: 129–134°F — warm red-pink center, tender and juicy - Medium: 138–145°F — warm pink center, firmer, still juicy - Medium-Well: 148–155°F — slight pink, firm, reduced juice - Well Done: 160°F+ — gray-brown throughout, dry, very firm
What determines doneness at the molecular level: The progressive denaturation of muscle proteins — primarily myosin (starts ~122°F) and actin (starts ~140°F). Myosin denaturation changes texture from raw-soft to tender-firm. Actin denaturation causes significant moisture loss. The transition between these two protein events is what separates "juicy" from "dry."
Important distinction: Doneness is a range, not a single point. "Medium-rare" spans roughly 129–134°F, and there's a meaningful difference between the low and high ends in terms of texture, color, and juiciness. Communicating your preference as a specific temperature rather than a category leads to more consistent results.
The USDA recommendation: The USDA recommends 145°F for whole-muscle beef with a 3-minute rest. This is a food safety guideline with a wide margin — not a quality recommendation. Most restaurants and professional cooks serve medium-rare steak at 130–132°F.