obviously cooking on very high heat is faster but it wouldn’t mean you could have a huge hunk of meat nice and tender in a couple hours. but why. i don’t even understand enough to know if i chose the right flair.
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Think of when you boil water to make some pasta. The water heats up until it start boiling, but then it stays at that temperature. If you turn the heat up it will start boiling “faster” but the water doesn’t actually get any hotter. In as ELI5 of a way as I can explain: this is because it takes a lot more heat energy to turn liquid water into steam than it takes to heat water up to a boil from room temp. Essentially all the heat you’re pushing into that water leaves with the steam, and the water stays the same.
Now how does this relate to the pressure cooker? The pressure of the air around you is what determines the temperature the water will boil at. If you got rid of the air and exposed your pot of cold water to a vacuum, it would boil. Likewise, increasing the pressure artificially inside the pressure cooker allows the water to boil hotter.
Science time!
Water doesn’t get hotter than 100 Celcius in a standard environment, no matter how hot the flame under the pot is. That’s just a science fact. If you want to cook something at higher temperatures and it’s in water, you have a problem. Adding salt does raise the boiling point a little bit but not that much.
If the air the water is boiling into were at higher pressures, then water will boil hotter than 100 C. This is what a pressure cooker is for.
Pressure cooking is a way of using higher heat than you can get in unpressurized pot.
On the stovetop, you are limited to the 212°F (the boiling point of water at average air pressure)
At the higher pressures, the boiling point of water is higher (you can reach 30 psi inside a pressure cooker, and that pressure, water boils at 250°F, giving you a hotter cooking cycle.
It is literally impossible for water (at sea level pressure) to be above 100°C. If it ‘got hotter’, it would be steam instead. Given that almost every thing we can consume has a bunch of water to it, the highest temperature you can cook something at sort of comes out to that 100°C too (the exceptions involve steam and cooking methods that partially dry out the food and things that end up with less water than you started with). Adding more heat to the burner doesn’t change that, except to dry the food out faster (which is usually an unpleasant texture anyway, as you noted).
But what about *not* at sea level pressure?
With more pressure, water boils at a higher point. Most pressure cookers can safely and conveniently reach 120°C boiling points, which allows the food to cook significantly faster *without* removing the water first. And of course, higher temperatures usually mean faster cook times.
So water boils at 100 degrees C, everyone knows that. What you may not know is that it is impossible for liquid water to ever get *hotter* than 100 degrees C. At that point, applying more heat energy will just make it convert to steam more rapidly, but only in the vapor form can it get hotter than boiling point.
That is, at normal sea-level air pressure that’s all true. If you increase the pressure, you increase the temperature of the boiling point and thus increase what is essentially the maximum temperature you can get your food to, and that’s what makes it cook faster.
Of course, this affect mostly only works when cooking something immersed in water or a mostly-water liquid (which is pretty much anything you would cook with other than fat) like soups, stews, or brazes. There is no physical effect that keeps air or metal from getting hotter than 100C so baking or grilling under pressure wouldn’t really do anything.
All this is the same reason that frying food in oil is so different than boiling it in water. Frying is done at much higher temperatures, usually 200C or more, which is not physically possible with water (unless the air pressure were around 20 bars). If you “fry” something in 100C oil the results will be very different.
If you just heat up the water in an open container at sea level it will not get warmer than 100C. Having a stove that outputs more heat does not result in water it just results in it boiling away faster, it do not get warmer then 100C
Water requires energy to become a gas and it rescues the temperature of the remaining water. The heat of the stove is required to keep the water at 100C. If you remove the heat the water that boils away cool down the rest a bit and it is below 100C and it not longer boiling.
If you boil water a higher altitude where the pressure is lower the building temperature of the water is lower at 1500meter is only 95C. So if you are in Denver Colorado that is at that elevation it takes longer time to boil food because the water do not get at hot.
If you put water in a vacuum chamber it boils at room temperature. It still requires practically the same amount of energy to turn to gas so the liquid water will cool down, and the boiling stops when the remaining water all has turned to ice.
If you on the other hand use a pressure cooker the internal pressure in it can be higher. So water will start to boil at 100C but only a bit before the pressure increase. The water can then heat up a bit more, you get a but more gas and the pressure increase. The pressure cooker has over-pressure valves, it is when it starts to relate steam that water boils normally, the temperature will be higher than 100C, exactly what depends on the pressure cooker.
Another way to make food cook faster is to replace water with a liquid that boils at a higher temperature. Cooking oil does that. So when we deep frying in oil you have a temperature of around 200C. You do not heat the oil so it starts to boil but a bit colder than that, oil do not just boild away but can break down too and start to taste bad.
A frying pan uses oil or other fat for the same reasons, it can get warmer then 100C. The same piece of meat can be done faster if you use a frying pan compared to if you cook it. A drawback is if it is too large the outside can get so warm it is destroyed before the inner is done. If you boild meat it never gets warmer then 100C, or even lower if you usd temperature controll like with Sous vide.
I always just imagined the pressure cooker forces the heat into the food with pressure. Whereas normal cooking just puts the heat around the food until it gets hot.
Steam carries a LOT of heat.
Heat a pot of water on the stove top. Take its temperature and you’ll see it ramp up evenly till it hits 100°C. There it will sit, sucking up heat, for a surprisingly long time, before it starts to boil. The heat it has taken in is sometimes called “latent heat.”
The resulting steam carries this latent heat and delivers it to whatever object it comes into contact with, so long as the object is cooler than 100°C. That’s why steam heating systems work, and that’s why steam cooks stuff fast.
In a pressure cooker, the food is trapped in the vessel with the steam, and new steam is constantly being made. That’s already going to do a great job of cooking many foods. The pressure adds to the effect by allowing the steam to be at a higher temperature. Instead of 100° it’ll get to 125° or so. This is a great temperature to break down connective tissue in many cuts of meat without causing the meat to seize. For veggies or beans the higher temperature speeds the cooking tremendously even though the food is just being boiled or steamed.
So an ELI5 asnwer.
-Water at regular sea level pressure boils at 100°C.
-Now take that same pot to the top of Mount Everest where there is less air pressure the water boils at a lower temp than 100°C. Maybe 90°C (I dont know)
-Now close the pot and increase the pressure and the water boils at a higher temp than 100°C.
-Boiling your pot of water in your kitchen at the maximum temp that your cooktop allows does not boil the water any hotter than 100°C, it only brings the water to a 100°C, faster, then it stays at 100°C.
The only difference is that you are wasting energy.
thank you everyone so much for your answers!! i understand so much better now, i never knew the boiling point of water was affected by pressure before, thank you!
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