In an effort to figure out why so many apple pies end up as train wrecks, the New York Times called in a biophysicist at UCLA who actually teaches about the subject.
…it turns out that there’s plenty to know, starting with the Maillard reaction, the chemical reaction between amino acid and a reducing sugar that gives the crust that perfect glow (make sure you bake over 375 degrees and brush with egg whites). Some other fascinating info nuggets include: Replacing some of the water with Rum or another alcohol will impede the formation of gluten (which toughens the crust); the tiny droplets of water that make up butter are what create air pockets in the crust; and a bit of flour will fend off runny filling, because its molecules are bigger and slower than water molecules.
Apparently the tiniest detail, from the shape of the apple slices, to the surface-area-to-volume ratio of the crust can affect taste, so nothing less than perfection will do.
Click on the image to enlarge.