Now it can be told: Why the cookie crumbles:
Scientists in Britain have discovered why biscuits seem to break so easily.
Using sophisticated laser techniques, physicists at the University of Loughborough, in the north of England, found that a biscuit develops “fault lines” a few hours after it comes out of the oven.
As it cools down, it picks up moisture around the rim, causing it to expand — while at the same time, moisture at the centre makes it contract.
The result is a build-up of strain forces which pulls the biscuit apart, making them vulnerable when handled, moved or packaged.