Heat never touches the middle of anything you cook. It only ever reaches a food's outer surface — by contact, by moving air or liquid, or by radiant energy — and from there it has to crawl inward on its own, one layer at a time. Which is why thickness costs far more than it looks like it should: double a cut and you roughly quadruple the time, because the heat is crossing twice the distance while warming twice the mass on the way. A two-inch pork chop is not a one-inch chop with minutes added. It is a harder problem.
Why heat only ever arrives at the surface
Cooking heat gets to food in exactly three ways, and every stove, oven, grill, and fryer is really just a different arrangement of them. Conduction hands off heat through direct contact — a skillet's metal touching a steak, molecule handing energy to molecule with nothing in between. Convection carries heat inside a moving fluid, whether that's air circulating in an oven or water churning in a stockpot; the fluid has to keep sweeping fresh, still-hot material against the food to keep the transfer going. Radiation skips a carrier entirely and reaches food as infrared energy, the way a broiler element or a bed of charcoal warms a steak sitting a few inches away without anything solid or liquid touching it at all.
All three do the same job: they get energy onto a food's outer surface. None of them, by itself, gets energy any deeper than that.
Why the inside is always running behind
Once heat lands on the surface, it has exactly one way left to travel — conduction, moving molecule to molecule through the food itself, regardless of how that surface got hot in the first place. A broiler delivers its energy by radiation, but the center of whatever sits under it still only warms up by conduction, same as if it were sitting in a pan. There is no shortcut past the outer layers.
That produces a temperature gradient inside every piece of food that's cooking: hottest at the surface, a little cooler with each layer in, coolest at the center, for as long as heat keeps arriving faster than it can spread. Cut a roast open right after it comes off the heat and that gradient is exactly what the color bands show — browned crust, then pink, then a core that has barely warmed.
Why a thick steak and a thin one are different problems
Conduction through food is slow, and it gets slower — not just longer, but disproportionately longer — the farther heat has to travel. Doubling a cut's thickness roughly quadruples how long it takes that gradient to reach the center, because the heat is crossing twice the distance while also warming twice the mass along the way. A 1-inch pork chop and a 2-inch one aren't the same recipe with extra minutes tacked on. The thick one is a genuinely harder heat-transfer problem, which is why so many thick cuts get seared first and finished lower and slower — it buys the center time to catch up before the surface goes from browned to burnt.
Why the medium touching the food sets a ceiling
Every one of the three delivery methods is limited by how hot its carrier can actually get, and that limit becomes the highest temperature the food's surface can ever reach. Air in an open oven can be pushed past 500°F (260°C). Oil in a fryer commonly runs 350°F to 375°F (175–190°C). An open pot of water, no matter how hard it boils, cannot get past 212°F (100°C) at sea level — adding more heat just makes it boil harder, not hotter.
That ceiling decides whether browning is even possible. The Maillard reaction, the one responsible for a seared crust, needs a surface somewhere north of 300°F (150°C) to run at a useful pace. Air and oil clear that easily. Water never does, no matter how long something simmers in it — which is the real reason a boiled potato stays pale and a fried one doesn't.