Thermal Gradient

A thermal gradient is the rate of temperature change across a distance — in steak terms, it's the difference in temperature between the outer surface and the geometric center. A steep thermal gradient means the outside is much hotter than the inside. A shallow gradient means the temperature is relatively uniform throughout.

The thermal gradient is the single most important concept in steak cooking science. It determines the width of the gray band (the overcooked zone between the crust and the medium-rare center) and is the variable that different cooking methods aim to control.

High-heat grilling creates steep gradients: When a steak hits a 700°F grill, the surface rapidly reaches 300°F+ while the center may still be 40°F (if started from the fridge). That 260°F differential is a steep gradient, and it means the outer layers overcook severely before the center reaches target temperature.

The reverse sear creates shallow gradients: A 250°F oven brings the steak up slowly. By the time the center reaches 115°F, the outer layers might be at 140°F — a 25°F differential. Much shallower. This is why the reverse sear produces edge-to-edge even doneness.

Sous vide eliminates the gradient entirely: The water bath holds an exact temperature. Given enough time, every point in the steak reaches that temperature — zero gradient.

Practical significance: The shallower the thermal gradient at the moment you stop cooking, the less gray band you'll have, the more uniform your doneness will be, and the less carryover cooking you'll experience.