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The Mechanics of Oreo Twisting

December 5, 2023

Oreo cookies, beloved for their delicious combination of creamy filling and wafer layers, have become the subject of a scientific study exploring the mechanical mysteries behind their unique properties. Researchers at MIT have delved into the science of Oreo cookies, investigating the distribution of their creamy center, the torque required to twist them open, and the fascinating behavior of the cream under stress.

Torque Measurements and Cream Texture

The researchers measured the torque needed to twist open an Oreo, revealing similarities to turning a doorknob and only a fraction of the force required to open a bottle cap. The cream’s failure stress, the force per area needed to deform it, was found to be twice that of cream cheese and peanut butter, resembling the stress magnitude of mozzarella cheese. The cream’s texture was classified as “mushy.” Adding milk into the equation revealed another layer of scientific wonder. Dunking Oreos in milk resulted in a decline in the elastic modulus of the wafer due to swelling. 

Cream Distribution Mystery

Despite variations in filling levels and flavors, the study found that the cream tends to separate onto one wafer rather than evenly between both. The researchers mapped this distribution and observed a tendency for the cream to stick to the inward-facing wafer, suggesting a post-manufacturing environmental effect.

FIG. 7. (a) While most creme layers failed adhesively in boxes of new cookies, (b) cookies exposed to adverse conditions may cause creme to spread from its initial manufactured state, and then cohesive failure was typical for most cookies in the box. These visual signs of changing creme fill levels (indicated by the black arrows in (a) and (b) are typical but not deterministic predictors of failure mode. (c) Failure tests also distinguished between cases in the computed stress–strain curves resulting from the measured torque as a function of imposed rotation angle. There was a single peak stress for adhesive failure, which occurs as a single delamination step, and two or more maxima in stress for cohesively failing creme layers due to the more complex dynamics of cohesive failure propagation along nonplanar surfaces. Cohesive failure was also typically observed to result in a higher failure strain and lower failure stress, as shown here.

Manufacturing Process Influence

Videos of the manufacturing process revealed that a slight time delay in placing the cream between wafers may contribute to better adhesion to the first wafer, influencing the subsequent distribution during twisting.

FIG. 1. (a) What happens when you twist an Oreo? (b) Eventually it splits into two parts, exposing the creme. (c) and (d) We observed that in a typical failure profile for Oreos from newly opened boxes, the creme most often tends to remain on one side, “wafer 1,” with a consistent orientation per box. In this case, wafer 1 faces to the left side of the upright box for a standard size package of regular Oreos. The creme occasionally splits between sides, often due to defects or small fractures in one or both wafers. (e) This is consistent for cookies with different creme levels, with a strong bias toward wafers facing one side of the box rather than the other, facing left for regular, right for double, and up for mega (where rows are oriented vertically rather than horizontally) in standard size packages.

The Oreometer

To make the study accessible and interactive, the researchers even designed a 3D-printable device called the “Oreometer,” allowing precise control over the twisting force applied to an Oreo. This device can be used for tabletop experiments and provides an opportunity for hands-on exploration of Oreo mechanics.

A 3D printed Oreometer is used to perturb cookies with scientific precision by applying a known and controlled torque. (a) In this device, (1) the cookie is mounted first into one half and then (2) the second half of the rubber band-powered clamps, which are then (3) placed into the vertical assembly mount. (4) “Penny castles” are mounted on the wings, and coins are successively loaded to one side to apply controlled torque until (5) the creme yields. (b) Results replicate values measured by the laboratory rheometer. (c) Photographs demonstrate the same tool, also including the rubber bands in two different arrangements designed to apply different levels of gripping strength in the clamps.

Confectionary Insights

The study not only provides a scientific investigation into the mechanics of Oreos but also opens possibilities for further exploration into the design of food materials. The researchers suggest that adding texture to Oreo wafers might enhance cream adhesion, leading to a more even split when twisted open.

In conclusion, Oreos offer more than just a delightful treat—they serve as a fascinating canvas for exploring the intricate science behind food materials and rheology.

References

Massachusetts Institute of Technology. (2022, April 19). Engineers introduce the Oreometer. ScienceDaily. https://www.sciencedaily.com/releases/2022/04/220419124037.htm

Owens, C. E., Fan, M. R., Hart, A. J., & McKinley, G. H. (2022). On Oreology, the fracture and flow of “milk’s favorite Cookie®.” Physics of Fluids, 34(4). https://doi.org/10.1063/5.0085362

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About Author

Hi everyone. My name is Julia, and I am a second year CS major. I joined StemComm and the Charged team to share my interests in food science, psychology, and computing!

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.