It's Brown, Not Browned
Why does a pot roast brown in a crockpot? It seems to be steaming in the pot, which one would think would create a blanched and pale cut of meat, but it comes out as browned as if we had seared it on the stovetop (not that I'm complaining).
As many people do, you're confusing two kinds of browning.
All red meat will turn brown when cooked by any method. As its temperature rises above 170 degrees, its red pigment, myoglobin, changes into metmyoglobin, which is brown. And that's all there is to that.
But the browning obtained by searing meat is created by a different high-temperature process called the Maillard reaction. And thanks for giving me the opportunity to shoot down a widespread misunderstanding about that.
When we sear a steak, for example, certain parts of the protein molecules (the so-called amino parts) interact with so-called carbonyl groups, which are parts of sugar molecules. When that happens, dozens of complex chemical reactions take place, producing a hodgepodge of dark brown, very flavorful compounds. That's why it's always good to sear meat before braising or slow-cooking it.
Now, did I say the Maillard browning reaction involves parts of sugar molecules?
Yes, I did.
Does that mean there are sugars in the meat?
Then what the. . . .
Easy, now. Let me explain.
A carbonyl group is indeed a certain grouping of atoms found in sugar molecules. But it also is found in many other kinds of molecules, including the meat's very own fats and proteins. The Maillard browning process can use the carbonyl groups that are inherent in the meat; it does not require sugars. And that's fortunate, because there are no sugars in meat, beyond perhaps traces of glycogen, a source of glucose that fades away following the animal's death.