Logo: University of Southern California

Engineering the Perfect PB&J

Joseph Greenfield trains future engineers using peanut butter and jelly.
By: Hai Vu
November 07, 2014 —

During one of his lectures, USC Viterbi Senior Lecturer Joseph Greenfield demonstrated the disastrous consequences of unclear instructions. Like a computer, Greenfield followed a student’s instructions to make a peanut butter and jelly sandwich exactly as stated. He flung slices of bread across the classroom because the student failed to explain how to take the slices of bread out of the bag properly. This miscommunication error is common in the computer sciences and engineering field and must be observed carefully.

The famous peanut butter and jelly sandwich, also affectionately known as the PB&J, holds a special place in many of our hearts. The sheer simplicity of the PB&J makes it one of the easiest dishes to be mastered by a six-year-old. This also makes the PB&J the ideal medium to help future engineers hone their engineering skills and get their creative juices flowing.

The peanut butter and jelly challenge. Photo by Michelle Park.

Greenfield teaches one of the Engineering Freshman Academy courses. The course focuses on developing the students’ engineering skills, exposing the students to the National Academy of Engineering 14 Grand Challenges, and deepening the students’ appreciation for the different fields of engineering. This week, Greenfield proposed a challenge for his class: optimize the given materials efficiently and create a strategic plan to engineer the perfect PB&J sandwich. Of course there’s a catch. Not only will the students have to design a game plan to attack and conquer their given task, but they also must take part in this competition in teams of five to mass produce drool-inducing PB&Js.

When asked how he came up with the idea, Greenfield said, “Two other faculty members at the Information Technology Program, Nathan Greenfield--my brother--and Trina Gregory use the example of assembling a peanut butter and jelly sandwich to explain algorithms to their programming students. I realized that the example demonstrates more than just algorithms. The simple concept of putting together a sandwich properly is easy for a human to understand but leaves a lot of room for interpretation.”

Although this may seem like an average culinary feat rather than one of the “14 Grand Challenges for Engineering,” it encompasses several different fields of engineering. Before beginning the challenge, each team must produce written instructions for each position on the assembly line. Students were randomly placed into six groups that consisted of five people. Potentially an industrial and systems engineer-to-be could be placed next to a chemical and biomedical engineer-to-be to replicate real life situations where a diverse group of engineers must work together to solve one of the “14 Grand Challenges for Engineering,” or in this case, mass produce mouth-watering PB&Js.

One team in particular consisted of two mechanical engineers, one biomedical engineer and two electrical engineers. They initially placed two people on the peanut butter station. However after a test run, they realized the jelly was incredibly difficult to spread and rearranged their team so two people were on the jelly station. Half way into the competition, the teams faced another obstacle: scooping out the last few bits jelly lying at the bottom of the jar with a knife that was too short to reach it. Several teams sacrificed one of their plates to scoop out the remaining jelly onto it. Some teams used a knife to scrape out the jelly, some used the help of gravity combined with rapid up and down motions created by erratically jumping around, and others opted to used their hands as a large spoon to scoop out the entire jar in a matter of seconds. This resulted in some sandwiches that were more aesthetically pleasing than others.

This challenge puts emphasis on industrial and systems engineering since the goal of this project is to create an efficient way to mass produce PB&Js with the materials given in a limited amount of time. If the team does not take into consideration the amount of time it takes to spread the dense peanut butter compared to jelly that glides on, it might result in a clump in the assembly line and thereby not fully utilize the workforce effectively. The team must work as a well oiled machine, which can only happen if the industrial and systems engineers optimize resources as well as the work forces proficiently.

It may not seem like it, but there are plenty of things that can go wrong when preparing a PB&J. Civil engineers must build a safe and stable bridge, while these engineers in training must build scrumptiously delectable PB&J sandwiches. Similar to the different floors of a building, the PB&J must be built in layers. The order of these layers plays a huge role in the building’s structural strength. You wouldn’t want your 20-story-high skyscraper to be missing a few steel beams because it will completely compromise the safety of the inhabitants, or in this case, the very epitome of the PB&J. After all, it wouldn’t be much of a PB&J if the peanut butter was missing!

In a real life situation, engineers must account for unexpected obstacles thrown their way. Sophia Spackova, a freshman in Greenfield’s course, said, “The mini challenges like changing the number of people we had per team from five to four, and giving us around five minutes to adapt is what happens in the real world. Situations change and we need to adapt to them to be great engineers.”

One team’s original plan required two people on the peanut butter station, one person on the jelly station, and two people to cut and bag the sandwiches. However, they were short a person on the cutting and bagging station. This was a big issue since one person was not fast enough to cut and bag everything by themselves which resulted in sandwiches piling up. To compensate, they stacked the PB&Js on top of one another and cut through all of them at once, like a layered cake.

In total, each class produced over 200 sandwiches. All of the beautifully crafted PB&Js were then donated to the local food bank so others can enjoy the taste of 21st century engineering at its finest.

PBJ 580
Photo by Michelle Henry and Michelle Park