When you twist open an Oreo cookie to get to the creamy center, you are mimicking a standard test in rheology — the review of how a non-Newtonian content flows when twisted, pressed, or otherwise stressed. MIT engineers have now subjected the sandwich cookie to arduous resources checks to get to the middle of a tantalizing question: Why does the cookie’s cream stick to just one particular wafer when twisted aside?
“There’s the interesting issue of striving to get the product to distribute evenly amongst the two wafers, which turns out to be genuinely difficult,” states Max Supporter, an undergraduate in MIT’s Department of Mechanical Engineering.
In pursuit of an response, the staff subjected cookies to regular rheology checks in the lab and located that no issue the flavor or amount of money of stuffing, the cream at the heart of an Oreo just about usually sticks to a person wafer when twisted open up. Only for older bins of cookies does the cream occasionally separate a lot more evenly amongst each wafers.
The researchers also measured the torque needed to twist open up an Oreo, and discovered it to be similar to the torque needed to flip a doorknob and about 1/10th what’s essential to twist open a bottlecap. The cream’s failure strain — i.e. the power per region needed to get the product to move, or deform — is two times that of cream cheese and peanut butter, and about the identical magnitude as mozzarella cheese. Judging from the cream’s reaction to tension, the group classifies its texture as “mushy,” alternatively than brittle, difficult, or rubbery.
So, why does the cookie’s cream glom to 1 facet alternatively than splitting evenly amongst both? The production system could be to blame.
“Videos of the manufacturing method exhibit that they set the first wafer down, then dispense a ball of cream onto that wafer ahead of putting the second wafer on leading,” claims Crystal Owens, an MIT mechanical engineering PhD prospect who scientific studies the attributes of elaborate fluids. “Apparently that minimal time hold off may possibly make the cream adhere improved to the first wafer.”
The team’s review isn’t simply just a sweet diversion from bread-and-butter analysis it is also an possibility to make the science of rheology accessible to some others. To that close, the scientists have intended a 3D-printable “Oreometer” — a simple device that firmly grasps an Oreo cookie and makes use of pennies and rubber bands to manage the twisting force that progressively twists the cookie open. Instructions for the tabletop device can be discovered listed here.
The new study, “On Oreology, the fracture and movement of ‘milk’s favored cookie,’” appears these days in Kitchen area Flows, a particular issue of the journal Physics of Fluids. It was conceived of early in the Covid-19 pandemic, when quite a few scientists’ labs had been shut or tough to obtain. In addition to Owens and Enthusiast, co-authors are mechanical engineering professors Gareth McKinley and A. John Hart.
A standard test in rheology places a fluid, slurry, or other flowable substance onto the base of an instrument known as a rheometer. A parallel plate earlier mentioned the foundation can be reduced on to the take a look at product. The plate is then twisted as sensors monitor the applied rotation and torque.
Owens, who consistently employs a laboratory rheometer to take a look at fluid products these as 3D-printable inks, could not help noting a similarity with sandwich cookies. As she writes in the new analyze:
“Scientifically, sandwich cookies present a paradigmatic design of parallel plate rheometry in which a fluid sample, the cream, is held amongst two parallel plates, the wafers. When the wafers are counter-rotated, the product deforms, flows, and ultimately fractures, top to separation of the cookie into two pieces.”
While Oreo cream may perhaps not show up to possess fluid-like properties, it is viewed as a “yield tension fluid” — a smooth stable when unperturbed that can start off to movement less than ample anxiety, the way toothpaste, frosting, specific cosmetics, and concrete do.
Curious as to no matter if many others experienced explored the link concerning Oreos and rheology, Owens found point out of a 2016 Princeton College analyze in which physicists initially described that without a doubt, when twisting Oreos by hand, the product virtually constantly arrived off on one particular wafer.
“We wished to create on this to see what really results in this result and if we could manage it if we mounted the Oreos meticulously onto our rheometer,” she says.
In an experiment that they would repeat for numerous cookies of many fillings and flavors, the researchers glued an Oreo to the two the major and bottom plates of a rheometer and used varying levels of torque and angular rotation, noting the values that properly twisted just about every cookie aside. They plugged the measurements into equations to compute the cream’s viscoelasticity, or flowability. For each experiment, they also famous the cream’s “post-mortem distribution,” or where by the cream ended up after twisting open.
In all, the staff went by way of about 20 boxes of Oreos, together with frequent, Double Stuf, and Mega Stuf concentrations of filling, and typical, dim chocolate, and “golden” wafer flavors. Incredibly, they identified that no issue the amount of product filling or taste, the cream pretty much generally divided on to 1 wafer.
“We experienced expected an impact primarily based on measurement,” Owens suggests. “If there was extra cream involving layers, it must be much easier to deform. But that is not truly the case.”
Curiously, when they mapped every single cookie’s final result to its primary placement in the box, they found the cream tended to stick to the inward-facing wafer: Cookies on the left side of the box twisted these kinds of that the product finished up on the suitable wafer, whereas cookies on the proper side separated with cream generally on the remaining wafer. They suspect this box distribution may perhaps be a consequence of submit-production environmental effects, these types of as heating or jostling that may result in product to peel a little absent from the outer wafers, even right before twisting.
The being familiar with obtained from the qualities of Oreo product could perhaps be applied to the structure of other complicated fluid elements.
“My 3D printing fluids are in the same class of products as Oreo product,” she claims. “So, this new understanding can aid me far better design and style ink when I’m striving to print adaptable electronics from a slurry of carbon nanotubes, because they deform in practically specifically the similar way.”
As for the cookie itself, she indicates that if the inside of Oreo wafers had been extra textured, the cream may grip far better on to equally sides and split additional evenly when twisted.
“As they are now, we found there is no trick to twisting that would split the product evenly,” Owens concludes.
This study was supported, in part, by the MIT UROP software and by the National Defense Science and Engineering Graduate Fellowship Plan.