Cereal Dust ! 
THE DILEMMA Ever notice when you open a box of granola that the nuts
and raisins are on top while smaller riffraff lingers at the bottom,
making it all but impossible to eat a well-rounded bowl of cereal?
This phenomenon is known as the “Muesli Effect,”
and it describes the tendency of different size particles to separate,
with the largest paradoxically ending up on top and the smallest down below.
It also occurs in bags of mixed nuts, which explains why Brazil nuts are always on top
(thus the alternate nickname, the “Brazil Nut Effect”), and in gardens,
which is why no matter how many rocks you remove from the soil, there are always more next spring,
rising up from the Earth’s depths.
It’s the bane of manufacturers, who (like you) prefer their mixtures to stay mixed, and since the 1930s,
leagues of cereal physicists have struggled to solve this puzzle. It defies logic:
Shouldn’t the bigger, heavier particles sink and the lighter, littler particles rise to the surface?
Some blame a process called “granular convection,” whereby larger particles float on top of the smaller granules,
which act like a liquid. Others point to percolation, in which the small grains trickle downward,
or “fluid drag,” which impacts how much particles move when they’re jostled.
THE SCIENCE SOLUTION While the Muesli Effect is still largely a mystery,
inroads have been made toward some solutions. In 1996, engineers led by Kurt Liffman
at the Advanced Fluid Dynamics Laboratory in Australia announced research showing
that the way containers are shaken during packaging could make a difference.
“By shaking a pile of particles ‘vertically,’ i.e. in the direction parallel to gravity, we obtain the ‘Muesli Effect,’
where the large particles, initially, rise to the top,” they said at a conference.
“Conversely, by shaking the box horizontally, we obtain the ‘reverse Muesli Effect,’ i.e.
where the large particles, initially, fall to the bottom.” Unsatisfied with the temporary cereal harmony,
engineers are still working on a new type of packaging that could keep the dust where it belongs.
THE QUICK FIX So what does this mean for average breakfasters craving both raisins
and crunchy oats in their morning cereal? If you open a box and see mostly large particles,
hold the box upright and shake it side to side to make them sink. Seems counterintuitive,
but it’s far more effective than turning the box upside down. Science proves it!
