The brown crust on grilled, roasted, or seared meat is not simply the meat drying out.
Much of that color and flavor comes from a group of reactions known as the Maillard reaction.
Heat brings amino acids and sugars together
Meat contains proteins.
Those proteins provide amino acids.
The surface also contains small amounts of sugars.
When the surface becomes hot enough, amino acids and certain sugars react.
The result is a large family of new molecules.
Those reactions create flavor and aroma
The Maillard reaction produces many of the roasted, savory aromas associated with cooked meat.
It also produces brown pigments.
That is why a browned steak tastes and smells very different from meat that was only gently warmed.
The same broad chemistry helps explain why toast turns brown.
Why does wet meat brown poorly?
Water limits the surface temperature while it is evaporating.
A wet surface spends time losing that water instead of climbing rapidly to the temperatures that favor strong Maillard browning.
That is why patting the surface dry can help.
Dryer surface.
Faster browning.
Does searing seal in the juices?
No.
That popular explanation does not hold up.
Browning changes surface chemistry.
It does not create a waterproof shell around the meat.
Juiciness depends on several factors, including how much the meat is cooked and how its proteins and water change.
How is this different from cooking an egg?
Why eggs turn solid when cooked is mostly about proteins unfolding and forming a network.
Meat experiences protein changes too, but the brown crust specifically depends heavily on high-temperature surface reactions.
Same kitchen.
Different chemistry.
Can browning go too far?
Absolutely.
Continue heating and desirable browning eventually becomes burning.
At that point, more material breaks down and bitter, charred flavors begin taking over.
There is a reason “beautifully browned” and “forgot it on the stove” are different recipe categories.
So the crust is not sealing in the juices.
It is creating a whole new set of flavor compounds on the surface.
And that’s the short explanation.
Related explanations: Why does toast turn brown?, Why do eggs turn solid when cooked?, and Why does salt make food taste better?