Snag AcademyThe cooker that never whistles
Steam hissing from the edge of the lid, no whistle, and food still hard after half an hour. There is a nice piece of physics behind why this happens.
Half an hour on the stove. Steam keeps escaping from around the edge of the lid. The whistle never goes. The lentils are still hard.
Everything is present. The pot, the lid, the heat, the water, the food. And yet it has stopped being a pressure cooker and become a heavy, noisy, ordinary pot.
What a pressure cooker is actually doing
Not "cooking with steam". Steaming is a different thing.
A pressure cooker works by trapping steam. Trapped steam has nowhere to expand into, so the pressure inside rises. And here is the useful bit: water boils at a higher temperature under higher pressure. Above 100°C, in fact.
That is the whole trick. It is not the steam that cooks fast, it is the extra temperature that the pressure allows. Ordinary boiling water cannot go past 100°C no matter how long you leave it on the flame.
So the seal is the machine
The rubber gasket ring that sits in the lid is what makes the pot airtight. No gasket, no seal. No seal, no trapped steam. No trapped steam, no pressure. No pressure, no temperature rise.
Steam escaping around the rim is not a small leak to live with. It is the symptom that the entire mechanism is not engaged.
The same physics, in reverse
This is why cooking takes longer at altitude. Air pressure is lower up a mountain, so water boils below 100°C, and food that boils at a lower temperature takes longer to cook.
A pressure cooker is that effect deliberately run the other way.
The answer
Show the answer
In the puzzle, what is missing is: the rubber gasket ring.
The tempting wrong answers are a bigger whistle, more water and an extra handle. Each looks like it addresses a symptom, and none of them restores the seal.
Talking about it afterwards
- "Where is the steam going, and why is that a problem?"
- "Why can't plain boiling water get hotter than 100°C?"
- "Which part here is doing the actual work? It is not the part that makes the noise."
Gaskets perish. If a cooker starts leaking round the rim, the ring is a cheap part and a genuinely good first thing to check.
Your child can work this one out for themselves in the app, with the picture running and the wrong answer playing out. It is free, and there is no sign-up. Open this case →
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