You do come up with some interesting off-the-vanderwaals questions, don't you?GlytchMeister wrote:Flour is also mainly cellulose, and flour is a big part of dough.
I don't know if Oreos use real flour or even real cellulose, but I bet the same action is happening.
Also, the sugar and fat dissolving probably contributes a lot, seeing as it's a freakin oreo.*
Flour is largely starch, and starch has a similar process taking place. When dried its molecules take a crystalline form; when wet, its molecules link to those of water (hydrogen bonds again, I suspect) and take the form of a gel.
Sugar, of course, is crystalline when dry, and syrupy-to-liquid when dissolved in water.
Oreo cookies contain sugar, wheat flour, high-fructose corn syrup, and cornstarch. So, when baked, when the water is forced out, the starch and sugar become crystalline and lock together to form a rigid mass. Reintroduce water, and the sugars will at least partially dissolve, and the starches will at least partially revert to a gel, and the structure loses its strength and falls apart.
Breads are made with high-protein flour; the protein molecules link together and create a network which doesn't dissolve readily after it's been baked. I'd guess that Oreos are made from pastry flour, which is a high-starch/low-protein type that doesn't create a stiff crust.