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Brazil nuts are not always sympathetic fruits.

As a supplier of numerous minerals and trace elements such as selenium, they are considered to be quite healthy.

But the large exotic species have a fairly high fat content of 60 to 70 percent and are naturally radioactive.

Their radium content is 1000 times higher than that of other foods.

They are also prone to mold, such as the poisonous aflatoxins.

Therefore, experts advise not to store the nuts for a long time, but to consume them quickly.

Source: Getty Images / © Daniela White Images

And as if that wasn't enough, there is also something else: you are always pushing your way through the bag and wanting to go upstairs.

This so-called Brazil nut effect does not only occur in fruits, but in many mixtures of different materials: In a mixture of large and small particles, under certain conditions, the large ones end up on top, although they are heavier.

Shaken, not stirred

This phenomenon has preoccupied researchers for decades - and not just in the morning when they are sitting in front of their cereal bowl.

Scientists at the University of Manchester wanted to uncover the secret.

For their study - published in the journal "Scientific Reports" - they shook a mixture of para and peanuts.

With the help of a high-performance computer tomograph, they observed and filmed the fruit in three dimensions.

So for the first time we could see how the Brazil nuts move up past the peanuts.

Philip Withers, materials researcher at the University of Manchester

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The video shows the movements of the nuts:

So they wander

Initially, the large Brazil nuts were in the lower third.

The movement made them rise while the smaller peanuts slid down.

The first Brazil nut reached the top tenth of the container after 70 shakers, two more after 150. Some Brazil nuts got stuck on the bottom for the entire experiment.

"We found that the Brazil nuts only begin to rise when they have rotated on their vertical axis, and when they have reached the surface, they finally turn back on their long side," explains the materials researcher and Study leader Parmesh Gajjar.

Brazil nut trees grow in the tropical rainforests of South America.

Here in the picture: the capsule fruit with peeled and unpeeled seeds.

Source: pa / WILDLIFE / D.Harms

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The Brazil nut effect only occurs when the large nuts are not at the bottom at the beginning.

Otherwise they cannot be bumped by the others, which means they can turn and straighten up vertically.

The small peanuts slide into the vacant spaces, pushing the Brazil nuts further upwards.

The knowledge of how mixtures behave not only plays a role for the morning muesli or the nut snack in between.

According to the researchers, it can help many industries to produce uniform mixtures - for example, when distributing the active ingredients in tablets or building materials.