The Physics of Frying Youtiao
Brandon Li
Award: Top 100
School: great neck north high school
Teacher: alan schorn
Category: Contrived
Photo #19359
The Physics of Frying Youtiao
I took this photo when my grandpa was frying "youtiao", or fried dough sticks, a traditional Chinese food. This photo captures three stages of the sticks: a raw, white stick sinking in the oil; a partially cooked, yellowish stick; and a fully cooked, brown stick floating on the surface. These stages reveal interesting physics behind the cooking process, specifically, heat conduction and expansion.
Heat conduction plays a critical role in cooking youtiao. The raw stick is thin and dense, and sinks due to its higher density compared to the oil. When the stick is submerged in hot oil, heat transfers from the oil to the dough and penetrates inside. As heat goes inward, the moisture inside the dough vaporizes and creates steam bubbles. The bubbles escape quickly and cause visible bubbling around the raw stick.
Expansion is also important because it makes the sticks puffy and delicious. The heat causes the dough to swell because the steam and carbon dioxide from baking soda creates pressure internally. The partially cooked stick becomes less dense and begins to rise. The fully cooked stick floats entirely due to its expanded volume and reduced density. The Maillard reaction, in which heat browns and flavors the dough, further transforms its surface into a golden brown, signaling it is ready.
This photo demonstrates how heat conduction causes expansion, which turns a piece of raw dough into a crispy stick. These physical phenomena not only create a delicious treat but also teach me the science in cooking.
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