London ? Why does a cookie crumble? Using a laser beam to closely monitor the fault lines of cookies emerging from an oven, a doctoral student appears to have figured out how bakers can stop disappointing their customers by shipping crumbled ones.

In fact, the discovery could result in the perfect cookie, or “biscuit,” as it is called in Britain. For generations, the “biccy” has been a key ingredient at afternoon tea, that middle-of-the-day tradition practiced by everyone from the queen to her servants.

Customers who find crumbled cookies in their packages often blame mishandling by the manufacturer, the shipping company or workers who load supermarket shelves.

But that’s not what Qasim Saleem, a doctoral student in mechanical engineering at Loughborough University in Leicestershire, and his colleagues discovered when they applied the complex and exalted field of physics to the mundane matter of cookies.

The discovery was published Thursday in Measurement Science and Technology, a journal of the Institute of Physics in London. It reads more like a technical treatise on fault lines in California than a report about fragile Oreos and Rich Tea biscuits.

Saleem and his colleagues closely monitored the surface of cookies as they cooled to room temperature.

Using a laser beam, the students followed the tiny deformations that evolve as the cookie picks up moisture around the rim, which causes it to expand, while losing moisture at the center, which causes it to contract. The resulting strains can pull the cookie apart, or leave it vulnerable to breakage before purchase.

The report said manufacturers often handled this problem by removing the offending cookies before they reached customers. However, no quality control system is perfect, so cookies with minor cracks often end up in packages.

A crumbly conundrum has been solved by scientists investigating why cookies such as this one crack up so often. Contrary to what most shoppers think, it has little to do with the way they are packaged and transported.

Saleem said the discovery should help cookie manufacturers adjust the humidity and temperature of their production lines to minimize cracking.

Richard Wildman, Saleem’s supervisor at Loughborough University, said the study was far from trivial.

Wildman said cookies were an incredibly complicated product of fats, solids and air, whose movements were hard to predict.

“You do need high technology from the aerospace industry and the power of modern physics and engineering to understand the complicated biscuit,” he said.