Scientists found themselves working from home with everyone else when universities closed their doors in the face of the COVID-19 pandemic — including labs, which posed a unique challenge to the experiment in particular. That’s how physicists from the University of Illinois at Urbana-Champaign found themselves looking for experiments that could be done at home in the kitchen. Physicists ended up investigating the physics of cooking pasta — first doing home experiments, then repeating the experiments more precisely in the lab once the university reopens.
The cooking instructions on most packaged dried pasta usually recommend a cooking time of 8 to 10 minutes, but it’s an inaccurate method that can make a great deal of difference in the consistency of cooked pasta. Among other findings, UIUC physicists have come up with a simple technique, using only a ruler, to determine when spaghetti is perfect. the dent, with no need for the time-honored tradition of throwing a cooked strand against the wall—although the latter requires less preparation. (And yes, you terrified Italians, the tasting method works well too. But where’s the fun in that?)
A research paper on their findings has been accepted for publication in the Journal of Fluid Physics, and two authors presented the work at this week’s meeting of the American Physical Society in Chicago. [UPDATE: the published article is now available.]
There have been a surprisingly large number of scientific papers seeking to understand the various properties of spaghetti, both in cooking and in eating – for example, the mechanics of smearing pasta in one’s mouth, or spitting it out (also known as the “reverse spaghetti problem”). Most famous is the question of how to make dry spaghetti strands neatly break into two pieces, rather than three or more scattered pieces.
French physicists succeeded in explaining the dynamics in a 2006 Ig Nobel Prize-winning paper. They found, contrary to what was expected, that dry spaghetti strands produce a “bounce” traveling wave when it breaks. This wave is temporary Increases Bending in other sections, which leads to more interruptions.
In 2018, Ars reported work by two MIT mathematicians who came up with a useful trick: rolling spaghetti at 270 degrees before slowly bringing the two ends together to snap the spaghetti into two. Twisting weakens the bouncing effect, and when the skein is twisted backwards and fades back to its original straightness, it will release the pent-up energy in the skein so there are no additional breaks.
In 2020, physicists at the University of California, Berkeley, provided a comprehensive explanation of why a strand of spaghetti in a pot of boiling water begins to sag as it softens. It then slowly sinks to the bottom of the pot, where it will curl back on itself to form a U-shape.
As mentioned at the time, spaghetti, like most pasta, is made with semolina flour, which is mixed with water to form a paste and then extruded to create the desired shape (in this case, a thin, straight rod). The commercial products are then dried – another active research area, as the threads are easy to crack during the process.
So what happens to dried spaghetti when submerged in boiling water? Only a few seconds are needed for the strands to reach the same temperature as the water, but it takes a little longer for the water to make its way through the pasta’s starch matrix. When this happens, the spaghetti swells, and small amounts of a starch called amylose seep into the water. Finally, starch gelatinization occurs, a chemical process that controls compositional changes, so well-prepared spaghetti is the dent.
Sameh Tawfik of UIUC, the first researcher on this latest work, naturally read the 2020 paper with great interest, given how it relates to his lab’s study. However, he noted, his team focused more on the surface adhesion and fusion of pasta strands, as well as coming up with a simple ruler measurement for determining when the pasta is perfectly cooked.
The pasta has proven to be well suited for at-home experiments during the COVID period, since Tawfik’s lab is researching soft materials, especially long fibres. Think threads, monofilaments, muscle, artificial muscle, and the like. “Pasta is long threads from our point of view,” Tawfiq said during a press conference at the meeting. “We study deformation, tangling, sticking and all of those things are in pasta.”
Sticking was the primary focus of the experiments at home – specifically, how the strands of spaghetti move sideways and stick together when one pulls the cooked pasta off the plate. Tawfik resembles this phenomenon with the so-called ‘chirio effect’, in which the last that delicious little “O” clumps together in the bowl: either drifts to the center, or to the outer edges.
The culprit is a combination of buoyancy, surface tension, and the so-called “meniscus effect,” which adds to a type of capillary activity. Cheerios mass is insufficient to break the surface tension of milk. But it is enough to put a small dent in the surface of the milk in the bowl, so that if two Cheerios are close enough, they will naturally drift towards each other. The ‘scratches’ fuse and the ‘O’ fuse together.
“If you have any particles floating on the surface of a partially submerged liquid, so part of the structure is in the liquid and part of the structure is outside the liquid, you will always have gravity if the particles are the same,” Tawfik said. Similarly, “if you have pasta of the same type, it will always come together.” This wouldn’t happen if some of the noodles were hydrophilic and some were hydrophobic; then there would be repulsion between them. “Instead of the surface tension that holds the noodles together, the surface tension will cause the two different types of noodles to repel,” he said. Fortunately for pasta lovers, he said. There is no such brutality.