The Physics of Steak

Why Cooking Is a Science Experiment You Can Eat

There’s a particular kind of disappointment familiar to anyone who’s ever tried to cook a steak: the surface browns beautifully, the sizzle is promising, the aroma is mouth-watering… and then you cut into it — and discover a cold, undercooked centre.

This isn’t just a culinary error. It’s a physics lesson.

Cooking is often treated as a creative art, full of intuition, instinct, and improvisation. But when it comes to understanding why your steak behaves the way it does, the answers are firmly rooted in the physical sciences — particularly heat transfer, diffusion, and phase transitions. In short: your kitchen is a laboratory, and steak is applied physics you can eat.

Heat Transfer: The Slow Journey from Surface to Centre

When a cold steak hits a hot pan, it undergoes a process called thermal conduction.

In this form of heat transfer, energy moves through direct contact — molecule by molecule — from the pan (usually a good conductor, like cast iron or stainless steel) into the meat (a significantly worse conductor).

But meat is complex. It’s made up of water, fat, muscle fibres, connective tissue, and dissolved salts — each of which conducts heat at different rates. Water, in particular, has a high heat capacity and acts like a thermal sponge, absorbing energy slowly. This makes the interior of a steak quite resistant to rapid heating.

So while the surface rapidly reaches the high temperatures needed for that golden-brown crust (via the Maillard reaction, which we’ll get to later), the interior remains stubbornly cool.

The Square Root Rule: Cooking Time vs. Heat Penetration

Here’s where things get mathematically interesting.

Heat penetration into meat follows a principle that can be loosely modelled by the square root of time. This means:

• To double the depth of heat penetration, you need four times the cooking time.
• Triple the depth? Nine times the duration.

In other words, cooking isn’t a linear process. It’s diffusive. The deeper you want heat to go, the more time it takes — quadratically more. This is why thick cuts of meat are so difficult to cook evenly.

Now, you might think the solution is to simply crank up the heat. But that’s like trying to thaw ice cream with a flamethrower: you’ll scorch the outside long before the inside comes around.

The Limits of High Heat: Carbonized Disappointment

Turning up the heat feels productive. After all, things sizzle faster, the aroma intensifies, and the crust forms quickly.

But this is largely an illusion. High external temperatures accelerate surface browning — yes — but do little to increase the rate at which heat penetrates the interior. You’re not speeding up cooking. You’re just burning the outer layers while the centre remains underdone.

In technical terms, the thermal gradient becomes too steep. The outside is overcooked, while the inside is raw. A better approach is to let heat diffuse more evenly before attempting to sear — which leads us to a smarter technique.

Reverse Searing: A Solution Rooted in Physics

Reverse searing has gained popularity among chefs and home cooks alike — and for good reason. It embraces physics instead of fighting it.

Here’s how it works:

1. Low-temperature cooking: You start by slowly bringing the steak up to temperature using gentle heat — in an oven, sous vide bath, or even indirectly on a grill. This allows heat to spread evenly and gradually from the outside to the core.
2. High-temperature searing: Once the steak is uniformly cooked to your desired internal temperature, you sear it quickly at high heat. This produces the flavourful crust without overcooking the interior.

By reversing the traditional order (sear first, then cook), you give the laws of heat diffusion time to do their job properly.

The Maillard Reaction: Chemistry You Can Smell

That crust you crave? It’s not just about browning — it’s chemistry in action.

The Maillard reaction is a complex series of reactions between amino acids and reducing sugars that occurs around 140–165°C (285–330°F). It produces hundreds of aromatic and flavourful compounds that give seared meat its distinctive taste and smell.

But this reaction requires dry, hot surfaces. If the meat is too wet or cold, it will steam rather than sear. That’s why you want the surface dry and the steak already warm from its slow cook before applying high heat.

Salt and Time: Flavour as Molecular Migration

Now let’s talk about flavour — and the widespread myth of last-minute seasoning.

Salt doesn’t magically disappear into the meat when you sprinkle it on the surface. It diffuses in slowly, governed by the same physics that dictate heat movement. This is a process of molecular diffusion, and it moves at — quite literally — a glacial pace.

Typical sodium ions may penetrate only a few millimetres into the meat over the course of an hour. To actually flavour the interior, you need to salt your steak several hours in advance, preferably overnight. This gives salt time to:

• Diffuse inward
• Begin breaking down muscle proteins
• Improve moisture retention and texture

Last-minute salting? That’s seasoning the crust, not the steak.

Marinades: Mostly for Show

Marinades are often assumed to “soak” into meat, but here again, physics disagrees.

Most flavour molecules in marinades — herbs, spices, sugars, acids — are large and hydrophobic. They don’t penetrate meat deeply. Without mechanical assistance (e.g., vacuum tumbling), marinades only flavour the surface.

Acids can denature proteins near the exterior, which changes texture and imparts a slight tang. But beyond a couple of millimetres, the marinade’s influence disappears. So while marinating can still be useful, don’t expect it to transform the interior.

The Resting Period: Let the Physics Finish

After cooking, your steak is not yet ready for the plate — or the knife.

Why? Because it’s still undergoing thermal equalization and fluid redistribution. Cutting too soon allows hot, pressurized juices to escape, leaving the steak dry and unevenly warm.

Letting it rest for 5–10 minutes allows:

• Heat to diffuse inward from hotter outer layers
• Juices to settle and redistribute through capillary action
• Proteins to reabsorb moisture

It’s not just tradition. It’s another step where physics quietly improves flavour and texture.

Conclusion: Food as a Scientific Process

To summarize, cooking a steak is not merely an act of following a recipe. It’s an intricate, multivariable process governed by:

• Heat conduction
• Molecular diffusion
• Chemical reactions
• Phase changes

You don’t need a lab coat to cook well — but you do need respect for the physical principles at play. Whether it’s reverse searing, pre-salting, or just letting your meat rest, every step is rooted in science.

And when you understand that science, you don’t just become a better cook — you become a more thoughtful observer of the physical world.

So next time someone says science is boring, hand them a steak.
Then tell them it took thermodynamics, chemistry, and time to make it taste that good.