Fun with Food Physics

Food is a fundamental need for every one of us. It is one of the things that first brought early humans together, and it continues to bring us together today. For some of us, food is sustenance, but if you are lucky enough, food is warmth, it’s art, it's culture, and it's love. From cooking meat on sticks over an open fire to mastering the delicate art of crafting the fluffiest soufflé, our understanding of food has come a long way.

"Food is dynamic and ever-changing," said Ezgi Pulatsu, postdoctoral fellow at the University of Ottawa and guest editor of the Special Issue on Food Physics in the Physics of Fluids publication. Have you ever wondered why the cream on Oreos sticks to one side? Or what the perfect beer pour is? Or how long to cook your pasta so it is neither uncooked nor a pile of mush? If so, food physicists probably have the answer for you.

Flowing chocolate inspired Pulatsu to pursue her interest in food physics. As a child in Turkey, Pulatsu would visit the local bakery on her way home from school. "They would give us a cup and fill it with Nutella," she said. "I always liked how it would flow through, its spreadability, and how it tasted." She later found that she could study these properties as a food engineer. Today, Pulatsu uses 3D printers to print out chocolate in various shapes, among many other things. "You could say my dream came true," she said, laughing. "I hope everyone working on something for this food physics issue is having as much fun as I am."

When San To Chan successfully finished his Ph.D. at the Okinawa Institute of Technology, some of his friends from the Massachusetts Institute of Technology sent them saltwater taffy, an American confection usually found at stores on beach fronts, to celebrate. Despite the candy's name, it contains no saltwater and is made from ingredients such as table sugar, water, oil, corn syrup, flavorings, and food coloring. "When I saw these colorful sticky sweets, my first instinct was to understand their rheology," said Chan. Rheology is a branch of physics that deals with how matter flows. Chan and the team from MIT together found that the taffy wasn't a solid or a liquid but was instead something in between. The air bubbles and oil droplets that are formed by pulling taffy are what give it this property. They found that adding emulsifiers like lecithin would enhance the chewiness and longevity of the taffy.

A second group of researchers from Ozyegin University wanted to increase the shelf life of gummy candy. "Biting into a hard treat is disappointing, even if it's still sweet," said researcher Suzan Tireki. "For gummies, texture is just as important as taste, if not more." The team found a direct relationship between the lengths of the bonds between the molecules of the gummy and their shelf-life. By adjusting critical factors such as starch, gelatin concentrations, and the ratio of glucose syrup to sucrose in the recipe, they assessed the sweets over 12 and 52 weeks at varying temperatures to find the optimal recipes for extended shelf life in different temperature environments. They found that the perfect gummy candy is made by balancing the glucose syrup to sucrose ratio and increasing the amount of gelatin and that it is best to store them at room temperature.

"If you are anything like me, you twist your Oreos open before dunking them in milk and eating them," said Crystal Owens, a physicist at the Massachusetts Institute of Technology. If you do what Owens does, you will realize that the cream sticks to one side of the Oreo almost every time. Owens hypothesized that the cream should split evenly between the two wafers if she twisted an Oreo perfectly. To test this, Owens and her team 3D printed what they call an Oreometer, powered by coins and rubber bands, to twist open an Oreo perfectly. "We found that no matter the flavor or amount of cream in an Oreo, the cream always sticks to one side." They suspect that the reason for this is due to the way the cookies are manufactured and then oriented during packaging.

Moving away from confections, new research at the University of Illinois, Urbana Champagne, shows how measurements with a ruler can confirm when spaghetti is fully cooked. The researchers’ primary work is studying the fluid-structure interaction of very flexible and deformable fibers. They found that as pasta absorbs water, its girth increases faster than its length until it reaches the desired texture. When lifted from water, the surface tension, the force that makes water molecules stick to each other, makes the noodles stick together, and the degree of cooking directly relates to the length that sticks together. If the length of pasta that sticks together is around half the total length of the pasta, then your pasta is cooked al dente, or firm to the bite.

If you like bread to complement your pasta, Ernesto Di Maio, a researcher with a yeast allergy at the University of Naples, found a way to make yeast-free bread. The team, including its professional baker/graduate student, prepared the dough by mixing water, flour, and salt and placing it in a hot autoclave, an industrial device designed to raise temperature and pressure. They evaluated their dough rheology and fine-tuned the pressure release to gently inflate bubbles to the desired extent inside the dough. They used air pressure to make the bubbles that are usually made by the yeast. "We had a lot of fun applying things we know well to delicious polymers instead of our typical and sometimes boring smelly plastics," said Maio. "The idea of approaching food samples with the same technologies and knowledge used for thermoplastic polymers was surprisingly successful!"

No meal is complete without a good drink. Beer foam plays a significant role in creating visually enticing drinks and delivering those delightful aromas for connoisseurs. Wenjing Lyu and his team partnered with Einstein 1, a startup developing a new bottom-up beer tapping system that uses a special glass with a magnet at the bottom to fill it from bottom to top. The team used numerical simulations to predict various features of beer foam. Their model can determine foam patterns, heights, stability, beer/foam ratio, and foam volume fractions. They used a computational approach called a multiphase solver to accurately simulate the bottom-up pouring process. The study also highlighted that higher temperatures and pressures lead to more foam. The researchers plan to optimize their computational methods further and study the effects of nozzle shapes to improve foam control and efficiency.

Most of these fun food experiments took place during the COVID-19 pandemic. Although some began as a fun project for bored physicists, they have all contributed towards understanding the physical properties of food, such as density, viscosity, and rheology. Food is complicated; it changes with time, decays, and reacts to its environment. Understanding these physical properties is essential to determining the best way to sustainably produce, distribute, and store foods. "When physicists around the world focus on these issues, we can make better decisions that will reflect both in industrial applications and every day in people's homes," said Pulatsu.