MIT scientists uncover why the cream in Oreo cookies sticks to one wafer after separation. (Image Credit: Mooss/pixabay)
Every Oreo fanatic wants to know the answer --- why does the cream filling always stick to one wafer after twisting and pulling both sides apart? Thankfully, MIT engineers have already dug into this famous cookie mystery with their 3D-printable Oreometer, a device that uses pennies and rubber bands to twist and separate the cookie wafers. With this newly-developed torque measurement device, the researchers investigated an Oreo cookie’s rheology, which involved intensive experiments.
“Videos of the manufacturing process show that they put the first wafer down, then dispense a ball of cream onto that wafer before putting the second wafer on top,” says Crystal Owens, an MIT mechanical engineering Ph.D. candidate studying the properties of complex fluids. “Apparently, that little time delay may make the cream stick better to the first wafer.”
In their experiments, the team glued an Oreo on a rheometer’s top and bottom plates and applied varying degrees of torque and angular rotation. They then noted each value that successfully twisted the cookie apart. Afterward, they fed these measurements into equations to calculate the cream’s viscoelasticity. After each experiment, the team also noted how much cream remained on each wafer.
The team used the 3D-printable Oreometer to apply varying degrees of torque to the Oreo cookie. (Image Credit: Crystal Owens/MIT)
In total, they used up twenty Oreo boxes, including Double Stuf, regular, and Mga Stuf levels of filling along with regular, dark chocolate, and golden wafer flavors. They discovered that the cream always ended up on one wafer regardless of the cookie’s filling amount or flavor. “We had expected an effect based on size,” Owens says. “If there was more cream between layers, it should be easier to deform. But that’s not actually the case.”
After mapping each cookie’s result to the original position in the box, they noticed the cream would usually stick to the inward-facing wafer. Cookies on the box’s left side twisted in a way where the cream stayed on the right wafer. Meanwhile, twisting the right-side cookies resulted in the cream sticking on the left wafer after separation. Post-manufacturing environmental effects, such as heat or jostling, could cause some cream to peel away from the other wafer before twisting.
This cream-filled experiment could be applied to complex fluid material designs. “My 3D printing fluids are in the same class of materials as Oreo cream,” she says. “So, this new understanding can help me better design ink when I’m trying to print flexible electronics from a slurry of carbon nanotubes, because they deform in almost exactly the same way.”
She also suggests that if the Oreo wafers had a better internal texture, then the cream could stay on both sides and separate more evenly when twisted. “As they are now, we found there’s no trick to twisting that would split the cream evenly,” Owens concludes.
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