Chemical Engineering in Everyday Life – Question 75: Do you know the principle behind popping popcorn?
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Today is the autumn equinox, and the corn is about to mature. I remember that when I was three or four years old, I had seen and eaten popcorn. After that came the Cultural Revolution; popcorn was considered part of the remnants of capitalism, so it disappeared completely. The next time it appeared was in the winter of 1977. I had a childhood without popping popcorn. Netizens who are five years older or younger than me, your attachment to popcorn shouldn’t lie in eating it, but rather in arguing with your mother over how much money to spend and getting a small container of corn, then going to queue up to hear that popping sound, right? When I was 5 to 13 years old, the only thing I could eat was fried popcorn – corn was placed in an iron pot and stirred continuously, with some kernels exploding with a pop. But the vast majority just get overcooked, or even mushy. It’s because I remember things early on; every time, I recall popcorn while eating it. Why does using a pot meant for popping popcorn yield popcorn that is so fluffy and evokes memories of childhood?
Not all corn can be turned into popcorn. This is why popcorn usually contains some dead kernels; only corn with a sufficient thickness to its outer shell and a high water content in its endosperm can meet this requirement. When corn is heated, the water in the endosperm turns into steam, causing its volume to expand rapidly and thereby causing the corn to \"explode\" instantly.
Genius! It provides knowledge for netizens, but this does not yet constitute a complete standard answer. Please continue to consider it from a chemical engineering perspective.
It’s the moment the lid of the popcorn maker is opened; the pressure inside the pot drops, while the pressure inside the corn kernels decreases more slowly. This pressure difference causes the corn kernels to expand and burst open. The reason why only some of the popped corn kernels explode is that the container remains open throughout the process; those kernels that do explode have intact husks that can effectively seal off the steam inside them, until the pressure exceeds the strength of the husk and it ruptures.
The original poster has come up with so many questions; it’s time to release the standard answers.
Got it! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !
I think of the movie Black 731: when the air pressure inside a room is lower than that outside, then the people inside… . . .
I must have wasted years eating popcorn without wondering why. Popcorn made from rice and corn is different – what’s the reason?
I think it’s like a hydrogen balloon: once it reaches a certain height and the external pressure decreases, it bursts – it’s a physical process. When it comes to things related to chemical engineering, one should use the knowledge regarding work and heat in chemical thermodynamics.
You’ve been fighting over this problem for decades! Genius
The container for making popped popcorn is a small furnace that is placed over a flame. There is a pressure gauge at the opening of the container, and experienced workers use time and pressure to determine when it’s time to start the process, that is, when the \"pop\" sound occurs； When I was young, I often watched this process; I can’t remember exactly what the pressure level was... The principle behind it is pressure difference. During the heating process, the corn kernels become cooked. There are also \"cavities\" inside the corn kernels, in the area of the germ. Under high temperature and pressure, the corn kernels change from raw to cooked, and the pressure inside those cavities increases as well. When this pressure is suddenly released, the corn kernels explode from the inside out. Thanks to the presence of endosperm and the seed coat (which are tough when cooked), they end up as round popcorn kernels.