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The Yield Stress Fluid Physics of Oreos


While most folks are familiar with the term “kitchen chemistry,” not many realize you can do fluid physics yield stress tests on ordinary household objects. Oreos, for instance. If you ever wondered why the cream almost always sticks to one side, you’re not alone. MIT researchers took a case of the munchies to whole new levels of exploration.

Twisting Oreos for science

DARPA is probably laying heavy coin out for this study. A group of researchers at MIT landed a grant to study complex fluids. The things they work on at the Massachusetts Institute of Technology often lead to earth-shattering discoveries which can be later be exploited by the Pentagon.

This time, they’re playing with Oreos. That stuff in the middle has interesting physical properties. The thing is, most people don’t even realize how interesting those properties can be.

Many consumers of Oreos habitually twist off the top layer. What they do with the individual halves after that is a matter of preference. Others either dunk and crumble or simply eat them raw.

For the twisters of the world, here are a few things to think about the next time you reach into the cookie jar. MIT even has some nifty 3-D printer plans if you want to get fancy and become a volunteer research assistant on the project.

Experts don’t twist their Oreos by hand. Since they’re legitimately testing the mechanical properties of the “stuff” in the middle, legitimate methodology of research calls for a “rheometer.”

The physicists who play with their food at work are called “rheologists.” What they’re really so fascinated with is the study of complex fluids. The stuff in the cookies is a lot more complex than you might imagine.


Give it a twist

The team never imagined that they would open up a new branch of science called “Oreology” but they did. The term simply means “flow study” of a Nabisco brand Oreo cookie. The “study of the flow and fracture of sandwich cookies” has gained official acceptance by publication in the peer reviewed journal “Physics of Fluids.” Their research was as fun as it was tasty.

That patented cream in Oreos is “a member of the class of flowable soft solids known as ‘yield stress fluids,’ which are fluids that act as soft solids when undisturbed and only flow under a sufficiently large amount of applied stress.

The stuffing inside Oreos is officially classified as “mushy.” That’s a scientific term that means instead of coming apart in the middle of the goop and leaving a coating on both sides, cookie filling sticks to one and releases from the other. The failure stresses and strains led graduate student first author Crystal Owens to conclude “We were able to characterize Oreo creme as quantitatively mushy.” Their standard mechanical twister wasn’t quite up to the job so they designed their own and 3-D printed it. The plans are available for all.

Their “Oreometer” studies “the influences of rotation rate, flavor, amount of creme, and environment” on stress characteristics. “One of the main things we can do with the Oreometer is develop an at-home education and self-discovery plan, where you teach people about basic fluid properties like shear strain and stress,” points out co-author Max Fan.

The results were surprising. “I had in my mind that if you twist the Oreos perfectly, you should split the creme perfectly in the middle. But what actually happens is the creme almost always comes off of one side.” Actually, it’s 95%.

Not only that, “within the boxes tested, 80% of cookies had creme–heavy sides oriented uniformly in one direction, rather than 50% as would be expected from random chance.” What happens depends mostly on rotation speed. “If you try to twist the Oreos faster, it will actually take more strain and more stress to break them. It’ll be easier if you do it a little bit slower.

What do you think?

Written by Mark Megahan

Mark Megahan is a resident of Morristown, Arizona and aficionado of the finer things in life.

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