Among nuts in a pile, or in a bag, Brazil nuts tend to end up at the top over time — and researchers have finally figured out that their shape is what helps them climb the pile. Photo courtesy of Max Pixel

April 19 (UPI) — If you’re not a fan of Brazil nuts, the initial handful from a bag of mixed nuts can be frustrating. While it may not be a consolation to frustrated snackers, scientists have finally figured out why Brazil nuts and other large nuts rise to the top.

The phenomenon known as the ‘Brazil-nut effect’ can be observed in freshly opened boxes of cereal, too, with the largest components rising to the top.

Scientists described their breakthrough in a new paper, published Monday in the journal Scientific Reports.

To better understand how the Brazil-nut effect works, physicists at the University of Manchester, in Britain, used time-resolved 3D imaging to observe the de-mixing process — noting how the size and shapes of different components influence their movements and interactions with other particles.

The challenge of studying conglomerate dynamics is tracking the movement components through the interior of a pile, where they’re out of view.

Researchers were able to solve this problem with the help of advanced imaging technologies at the National Research Facility for Lab-based X-ray Computed Tomography, located at Manchester’s Henry Royce Institute.

“In this work, we followed the motion of the Brazil nuts and peanuts through time-lapse X-ray Computed Tomography as the pack was repeatedly agitated,” co-author Philip Withers said in a press release.

“This allowed us to see for the first time the process by which the Brazil nuts move past the peanuts to rise to the top,” said Withers, a professor of materials at Manchester.

The novel 3D imagines captured by the NXCT instruments showed peanuts filtering downward as three large Brazil nuts rose to the top as the mixtures were shaken slightly.

After 70 shear cycles, or subtle vibrations, one of the Brazil nuts had reached the upper layer of the mixture. After 150 cycles, the other two nuts joined the first at the top. The other Brazil nuts remained trapped at the bottom.

“Critically, the orientation of the Brazil nut is key to its upward movement,” said lead author Parmesh Gajjar, material scientist at the Henry Royce Institute.

“We have found that the Brazil nuts initially start horizontal but do not start to rise until they have first rotated sufficiently towards the vertical axis. Upon reaching the surface, they then return to a flat orientation,” Gaijar said.

The study’s authors suggest their paper is one of the first to highlight the importance of particle shape and orientation in dictating the segregation process.

Moving forward, scientists hope to use the advanced imaging capabilities at NXCT to measure de-mixing dynamics in other types of conglomerates.

“This will allow us to better design industrial equipment to minimise size segregation thus leading to more uniform mixtures,” Gajjar said. “This is critical to many industries, for instance ensuring an even distribution of active ingredients in medicinal tablets, but also in food processing, mining and construction.”