Mathematical Model Shows Why Spaghetti Curls When Cooked – Popular Mechanics

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  • Scientists have made a mathematical model to explain why spaghetti curls as it cooks.
  • Dry pasta is pretty widely studied, maybe because it’s a nearly universal product.
  • The researchers found that the changes between the saturated outside and dry interior largely explains the curling.

    Scientists, as they are wont to do, have analyzed the way spaghetti curls as it cooks. Researchers Nathaniel Goldberg and Oliver O’Reilly, of U.C. Berkeley’s Department of Mechanical Engineering, used their noodles—we’re so sorry—to put together a mathematical model that accounts for gravity, density, elasticity, and rigidity in cooking “rod-shaped” noodles like spaghetti.

    Anyone who has ever well-meaningly dropped an entire pound of pasta into a too-small pot knows how much dry pasta swells and grows as it cooks. Dry pasta is rigid, but it absorbs water uniformly as it grows and becomes elastic. The researchers began with an observation that spaghetti standing in a pot of boiling water always ends up sagging the same way, which makes intuitive sense because of gravity and the growing bend-ability of the portion that’s in the boiling water.


    Images of the deformed rod at each of the three stages of the simulated process: (a) sagging, (b) settling, and (c) curling. The points s=0,s=γ1,s=γ2, and s=L are highlighted.

    U.C. Berkeley

    But a finished spaghetti noodle wants to curl, more than you’d expect for something that starts out mechanically straight and even. Why is that?

    It’s funny to think of spaghetti as a “rod,” but the idea of rod theory is kind of a novelty within mathematics. A rod is three-dimensional, but it’s also kind of not. It’s a line in real life! “Our approach has parallels to the use of rod theories for the mechanics of slender bodies undergoing growth and is inspired by a wealth of experimental data from the food science literature,” the researchers wrote in their abstract.

    To learn more, the scientists carried out several experiments “that [included] soaking noodles in room-temperature water for several hours to see if they would bend the same way,” per the press release. Soaking is a novel way to reduce cooking time later or better prepare pasta to be baked without getting overcooked and squishy. The mathematical model could help explain in even more detail why pasta can’t just be soaked instead of boiled, based on the chemistry of when starch is activated and how it behaves at different temperatures.

    So why is spaghetti so different from another similar rod that’s not boiled?

    “An initially straight elastic rod that is bent by gravity will return to its initial shape when placed on a flat surface, an outcome not seen for spaghetti that has been cooked for even a few tens of seconds,” according to a summary of the research in Physics. “[I]t’s the change from rigid to viscoelastic behavior—and the strand’s resulting ability to develop curvature and permanently deform without breaking—that drives the shape change,” the authors explain.


    The effect of hydration on a typical spaghetti strand’s cross section.

    U.C. Berkeley

    In other words, spaghetti curls because it can, dammit, and because the entire length of dry spaghetti has potential to grow elastic and curl. Boiling water penetrates in stages while the core is the last part to grow soft and elastic, so the outside is rapidly growing in volume while being constricted somewhat by the stubborn interior. This is a natural ratio for bending and, in spaghetti’s case, curling. But what about bucatini, which is a thicker spaghetti shape with a hollow center? Maybe the researchers will follow up.

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