In new research, a team of researchers at the University of Illinois at Urbana-Champaign has documented how pasta — composed of starch granules — swells and softens as a function of the cooking duration, water temperature, and the addition of salt. They’ve combined measurements of different pasta parameters to solve a variety of equations to form a theoretical model for the swelling dynamics of starch materials.
Hwang et al. studied the capillary-induced coalescence of swelling pasta; they observed that, as pasta is cooked (hence, swollen and softened), capillary action more easily deforms the noodle, and two pasta noodles can coalesce with the shorter stick length: (a) picture of spaghetti aglio e olio; capillary adhesion between the noodles is induced by olive oil seasoned with garlic and pepper; (b) pasta radial and axial growth over time at 100 degrees Celsius cooking due to hygroscopic swelling; radial strain grows up to 70% of its original and axial strain up to 40% of its original after 30 min of cooking (at 100 degrees Celsius); pasta cross section shows color-gradient before it is sufficiently cooked. Image credit: Hwang et al., doi: 10.1063/5.0083696.
“Exploring the properties of noodles was a straightforward pivot from the lab’s main work of studying the fluid structure interaction of very flexible and deformable fibers, hairs, and elastic structures,” said Dr. Sameh Tawfick, a researcher in the Department of Mechanical Science and Engineering and the Beckman Institute for Advanced Science and Technology at the University of Illinois at Urbana-Champaign.
“Over the last few years, we joked about how pasta noodle adhesion is very related to our work.”
“We then realized that specifically, the mechanical texture of noodles changes as function of cooking, and our analysis can demonstrate a relation between adhesion, mechanical texture, and doneness.”
In the study, Dr. Tawfick and colleagues observed how the noodles come together when lifted from a plate by a fork.
This provided them with a grounding of how water-driven hygroscopic swelling affects pasta’s texture.
As pasta cooked, the relative rate of the noodle’s increase in girth exceeded the rate of lengthening by a ratio of 3.5 to 1 until it reached the firm texture of al dente, before becoming uniformly soft and overcooked.
As pasta is pulled from liquid, the liquid surface energy creates a meniscus that sticks noodles to one another, balancing the elastic resistance from bending the noodles and aided by adhesion energy from the surface tension of the liquid.
The degree to which a noodle was cooked was directly related to the length of the portion that adhered to its neighbors.
“What surprised us the most is that the addition of salt to the boiling water completely changes the cooking time,” Dr. Tawfick said.
“So, depending on how much salt is added to the boiling water, the time to reach al dente can be very different.”
The team’s results appear this month in the journal Physics of Fluids.
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Jonghyun Hwang et al. 2022. Swelling, softening, and elastocapillary adhesion of cooked pasta featured. Physics of Fluids 34: 042105; doi: 10.1063/5.0083696
Source link: https://www.sci.news/physics/pasta-swelling-elasticity-adhesion-10715.html
