proteins in animals and plants behave in
exactly the opposite way: heat causes them to
unfold from their normally compact shape,
become entangled, and form strong bonds
with each other, so that they coagulate
permanently and irreversibly into a firm solid.
Thus liquid eggs solidify, pliable muscle
tissue becomes stiff meat, and milk curdles.
Of course a solid piece of coagulated protein
can’t be a sauce. But it’s possible to control
protein coagulation so that it can give body to
sauces.
Protein thickening and curdling. Two possible
outcomes of heating egg proteins, which start
out folded in compact shapes (left). If
conditions favor their unfolding, they form a
loose network of long chains (center) and