When you twist open an Oreo cookie to get to the creamy centre, you’re mimicking a conventional test in rheology — the study of how a non-Newtonian material flows when twisted, pressed, or usually pressured. MIT engineers have now subjected the sandwich cookie to rigorous elements assessments to get to the center of a tantalizing issue: Why does the cookie’s product adhere to just a person wafer when twisted aside?
“There’s the fascinating challenge of hoping to get the cream to distribute evenly between the two wafers, which turns out to be truly really hard,” suggests Max Admirer, an undergraduate in MIT’s Section of Mechanical Engineering.
In pursuit of an remedy, the crew subjected cookies to normal rheology assessments in the lab and located that no make a difference the flavor or volume of stuffing, the product at the center of an Oreo almost normally sticks to one particular wafer when twisted open up. Only for more mature boxes of cookies does the cream sometimes different far more evenly amongst the two wafers.
The researchers also measured the torque demanded to twist open up an Oreo, and uncovered it to be comparable to the torque essential to transform a doorknob and about 1/10th what’s necessary to twist open a bottlecap. The cream’s failure tension — i.e. the force per area essential to get the product to move, or deform — is two times that of cream cheese and peanut butter, and about the same magnitude as mozzarella cheese. Judging from the cream’s reaction to anxiety, the team classifies its texture as “mushy,” instead than brittle, challenging, or rubbery.
So, why does the cookie’s cream glom to a single facet rather than splitting evenly between the two? The production approach may be to blame.
“Videos of the production system clearly show that they put the first wafer down, then dispense a ball of product onto that wafer just before placing the 2nd wafer on major,” claims Crystal Owens, an MIT mechanical engineering PhD candidate who scientific studies the attributes of elaborate fluids. “Apparently that little time delay could make the cream stick far better to the to start with wafer.”
The team’s study isn’t just a sweet diversion from bread-and-butter study it’s also an prospect to make the science of rheology obtainable to other people. To that conclusion, the researchers have built a 3D-printable “Oreometer” — a straightforward product that firmly grasps an Oreo cookie and makes use of pennies and rubber bands to regulate the twisting drive that progressively twists the cookie open. Guidelines for the tabletop product can be found below.
The new analyze, “On Oreology, the fracture and stream of ‘milk’s favored cookie,’” seems today in Kitchen area Flows, a unique difficulty of the journal Physics of Fluids. It was conceived of early in the Covid-19 pandemic, when quite a few scientists’ labs have been shut or tough to obtain. In addition to Owens and Fan, co-authors are mechanical engineering professors Gareth McKinley and A. John Hart.
A regular exam in rheology destinations a fluid, slurry, or other flowable materials on to the base of an instrument acknowledged as a rheometer. A parallel plate above the base can be lowered on to the test materials. The plate is then twisted as sensors monitor the utilized rotation and torque.
Owens, who consistently takes advantage of a laboratory rheometer to exam fluid products these kinds of as 3D-printable inks, couldn’t assistance noting a similarity with sandwich cookies. As she writes in the new research:
“Scientifically, sandwich cookies existing a paradigmatic model of parallel plate rheometry in which a fluid sample, the product, is held among two parallel plates, the wafers. When the wafers are counter-rotated, the product deforms, flows, and in the long run fractures, foremost to separation of the cookie into two items.”
Although Oreo cream might not surface to have fluid-like homes, it is regarded a “yield stress fluid” — a tender good when unperturbed that can start out to circulation less than ample tension, the way toothpaste, frosting, specific cosmetics, and concrete do.
Curious as to regardless of whether other folks experienced explored the connection involving Oreos and rheology, Owens uncovered mention of a 2016 Princeton College study in which physicists to start with noted that in fact, when twisting Oreos by hand, the product almost generally came off on one particular wafer.
“We desired to develop on this to see what really leads to this result and if we could regulate it if we mounted the Oreos meticulously on to our rheometer,” she says.
In an experiment that they would repeat for many cookies of a variety of fillings and flavors, the researchers glued an Oreo to both the major and base plates of a rheometer and applied different degrees of torque and angular rotation, noting the values that successfully twisted every cookie apart. They plugged the measurements into equations to work out the cream’s viscoelasticity, or flowability. For each and every experiment, they also pointed out the cream’s “post-mortem distribution,” or where the product ended up right after twisting open up.
In all, the crew went by about 20 containers of Oreos, which includes common, Double Stuf, and Mega Stuf ranges of filling, and frequent, dim chocolate, and “golden” wafer flavors. Amazingly, they uncovered that no subject the amount of cream filling or flavor, the cream just about usually separated onto 1 wafer.
“We had anticipated an impact based mostly on measurement,” Owens claims. “If there was much more product between levels, it really should be easier to deform. But that’s not essentially the case.”
Curiously, when they mapped each and every cookie’s final result to its unique position 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 cream finished up on the correct wafer, whereas cookies on the correct side divided with product typically on the still left wafer. They suspect this box distribution may be a outcome of write-up-manufacturing environmental effects, this kind of as heating or jostling that may perhaps lead to product to peel marginally away from the outer wafers, even right before twisting.
The knowing attained from the properties of Oreo product could possibly be used to the style and design of other intricate fluid supplies.
“My 3D printing fluids are in the exact course of components as Oreo cream,” she says. “So, this new comprehension can assist me much better structure ink when I’m seeking to print versatile electronics from a slurry of carbon nanotubes, for the reason that they deform in virtually just the exact way.”
As for the cookie by itself, she suggests that if the inside of of Oreo wafers have been extra textured, the cream might grip far better onto the two sides and break up additional evenly when twisted.
“As they are now, we discovered there is no trick to twisting that would break up the product evenly,” Owens concludes.
This investigation was supported, in component, by the MIT UROP program and by the National Defense Science and Engineering Graduate Fellowship System.