Frozen broccoli thermodynamics

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Discussion Overview

The discussion revolves around the thermodynamics involved in cooking frozen broccoli in a microwave, specifically focusing on the phenomenon of a cover being sucked into a bowl due to differential air pressure. Participants explore the mechanisms behind this occurrence, including the effects of boiling water and steam condensation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that the cover was sucked into the bowl after heating, suggesting that air was expelled during heating and then cooled, creating a vacuum.
  • Another participant speculates that intermittent boiling of water due to the microwave's hot spots led to steam condensing, which could have caused the cover to be sucked down.
  • A different viewpoint suggests that rapid evaporation of water created a significant amount of water vapor, which condensed upon cooling, contributing to the pressure change.
  • Some participants share personal experiences with plastic wrap being sucked down onto food, indicating a similar phenomenon occurs with other cooking methods.
  • Concerns are raised about the safety of using plastic wrap in microwaves, including potential melting and the release of volatiles that could affect food taste.
  • A participant humorously comments on the taste of broccoli cooked for six minutes, suggesting an alternative cooking method involving olive oil and roasting.

Areas of Agreement / Disagreement

Participants express various hypotheses regarding the mechanism of the cover being sucked into the bowl, with no consensus reached on a single explanation. There are also differing opinions on the safety and taste implications of using plastic wrap in microwaves.

Contextual Notes

Participants discuss the effects of temperature changes and steam dynamics without resolving the specific mechanisms involved. The discussion includes anecdotal evidence and personal cooking experiences, which may not provide a comprehensive scientific analysis.

Who May Find This Useful

Individuals interested in cooking techniques, thermodynamics in food preparation, and safety considerations when using plastic in microwaves may find this discussion relevant.

Frabjous
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I was cooking frozen broccoli in a microwave with a couple of tablespoons of water in a plastic bowl. I left the cover loose to prevent steam pressurization. When I opened the microwave, the cover had been sucked into the bowl due to differential air pressure.

What is the mechanism?
 
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Frabjous said:
I was cooking frozen broccoli in a microwave with a couple of tablespoons of water in a plastic bowl. I left the cover loose to prevent steam pressurization. When I opened the microwave, the cover had been sucked into the bowl due to differential air pressure.

What is the mechanism?
First it heated up (air out), then it cooled down (tried to suck air back in).
 
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Frabjous said:
What is the mechanism?
I would speculate that the water in the plastic bowl was intermittently boiling due to rotation of the bowl in to and out of the "hot spot" in the microwave. Meanwhile, the ambient temperature within the microwave was below the boiling point. This led to the steam in the bowl condensing and sucking the top on.

This is similar to home canning except for the time scale.
 
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Frabjous said:
I was cooking frozen broccoli in a microwave with a couple of tablespoons of water in a plastic bowl. I left the cover loose to prevent steam pressurization. When I opened the microwave, the cover had been sucked into the bowl due to differential air pressure.

What is the mechanism?
I suspect that enough water evaporated quickly enough so that a significant fraction of the atmosphere in the bowl was water vapor. Upon cooling much of the water vapor condensed - perhaps relatively quickly.

(jbriggs44 beat me to it. )

How well was the broccoli cooked?
 
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SammyS said:
How well was the broccoli cooked?
About right. It was in for six minutes.
 
Sometimes I stretch plastic wrap over the dish/bowl to prevent spatter. Even if I open the door immediately when the timer ends, the wrap will be sucked down onto the contents. It doesn't take long!
 
gmax137 said:
Sometimes I stretch plastic wrap over the dish/bowl to prevent spatter.
Often a deprecated approach.

The plastic has been known to melt and/or even catch fire.

Many people dislike the taste and/or smell of the outgassing of volatiles from the plastic -- and don't care to ingest those volatiles as they drip back down to the food.

Safer to put a plate over the bowl.

Stay safe,
Tom
 
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Tom.G said:
Many people dislike the tast and/or smell of the outgassing of volatiles from the plastic
It can't hurt broccoli. Just kidding.
 
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Frabjous said:
What is the mechanism?
1. Boiling
2. Flushigf most of the air out
3. Remaining water vapor condensed
 
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Tom.G said:
Often a deprecated approach.

The plastic has been known to melt and/or even catch fire.

Many people dislike the taste and/or smell of the outgassing of volatiles from the plastic -- and don't care to ingest those volatiles as they drip back down to the food.

Safer to put a plate over the bowl.

Stay safe,
Tom
He cooked it for six minutes. It's already awful.

Top tip - add olive oil and salt and roast for 20 minutes at 180.
 
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BigInit said:
He cooked it for six minutes. It's already awful.

Top tip - add olive oil and salt and roast for 20 minutes at 180.
This↑
 
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