Paper Number
PO19
Session
Poster Session
Title
Oreology: Fracture and flow of “milk’s favorite cookie”
Presentation Date and Time
October 13, 2021 (Wednesday) 6:30
Track / Room
Poster Session / Ballroom 1-2-3-4
Authors
- Owens, Crystal E. (MIT)
- Fan, Max R. (MIT)
- Hart, A. John (MIT, Mechanical Engineering)
- McKinley, Gareth H. (Massachusetts Institute of Technology, Mechanical Engineering)
Author and Affiliation Lines
Crystal E. Owens, Max R. Fan, A. John Hart and Gareth H. McKinley
Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA
Speaker / Presenter
Owens, Crystal E.
Keywords
experimental methods; additive manufacturing; applied rheology; non-Newtonian fluids; rheology methods
Text of Abstract
Understanding the flow behavior of food ingredients and products has widespread impact on economies of production, public health, and individual diets. Though unstudied compared to starches, doughs and condiments, sandwich cookies present an ideal model of parallel plate rheometry, in which a fluid sample (the cream) is held tenaciously but temporarily between two parallel plates (the wafers). When the wafers are counter-rotated, the cream deforms, flows and fractures, leading to separation of cookie halves. To address this gap, we introduce Oreology (/?ri?'?l?d?i/), from the Nabisco oreo<\i> for “cookie” and the Greek rheo logia<\i> for “flow study,” as the study of the flow and fracture of sandwich cookies. We measure linear and nonlinear mechanics of the eponymous oreo and probe the dependence of post-mortem cream distribution on the kinematic protocol used to separate wafers. A bespoke 3D-printed fixture (PLA; Ender 3) holds wafers on a DHR3 rheometer with a rubber band-powered clamp to transfer torsion without cracking brittle wafers.
Results show adhesive failure in which nearly all (95%) cream remains on one wafer after failure. We ascribe this to the production process, as we find that the cream-heavy side is uniformly oriented within most boxes of oreos. The full failure event has elasto-visco-plastic nature, with a linear elastic modulus of 110kPa, yield stress of 10kPa and yield strain of 10%, followed by cream rupture at 30% failure strain. Mechanics are independent of rate and direction, and consistent for Original, Double and MEGA Stuf cookies and for Golden and Dark Chocolate varieties. However, failure can be altered when the cream is reflowed to promote adhesion/soften cream, such as by moderate heating (>30°C or ~12s in a microwave), after which cream splits more evenly by cohesive failure. Future studies may examine other sandwich-variety cookies, such as custard creams, macarons, and ice cream sandwiches. At-home tests are encouraged to contribute to this incipient field of study.