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I noticed today that the water warmed up in pressure cooker (1.5 ATM) dissolves sugar much faster and much more than water cooked in 1 ATM.

I am interested in how long can water hold the high pressure after opening the lid. I noticed also that the sugar crystallized much more in the 1 ATM-cooked water than in 1.5-ATM-water.

How long can boiled water at 1.5 ATM hold its pressure and energy after opening the lid of the pressure cooker? I think the water can hold the water rather long time so keeping the temperature longer. However, I am interested in how much this could be, for instance if the volume of the pressure cooker is 2.5 liters.

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I noticed today that the water warmed up in pressure cooker (1.5 ATM) dissolves sugar much faster and much more than water cooked in 1 ATM.

The effect you observe is one of temperature, not pressure. Water soluble substances dissolve quicker when the temperature is higher because the water molecules of hotter water have a higher average kinetic energy than those of colder water.

Water does boil at higher temperature when held at higher pressure, that's the principle of a pressure cooker: decrease cooking times by increasing boiling temperature by increasing pressure.

How long can boiled water at 1.5 ATM hold its pressure and energy after opening the lid of the pressure cooker?

The water loses its pressure almost instantaneously after opening the pressure cooker and water temperature also drops back to about $100 \text{ centigrade}$ very, very quickly, the boiling point at atmospheric pressure.

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  • $\begingroup$ Can you estimate how quick is the drop of water from 1.5 ATM to 1.0 ATM? I managed to much more sugar to such water than boiled water at 1.0 ATM. $\endgroup$
    – Léo Léopold Hertz 준영
    Commented Oct 2, 2015 at 13:04
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    $\begingroup$ @Masi: make sure you degas the coke completely! $\endgroup$
    – Gert
    Commented Oct 2, 2015 at 13:57
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    $\begingroup$ All pressure cookers I know of have a pressure relief valve (actually more of a pressure setting valve, but...). The carbon dioxide will come out well before boiling starts. $\endgroup$
    – Jon Custer
    Commented Oct 2, 2015 at 14:23
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    $\begingroup$ @JonCuster: it's just a calibrated weight that sits on top of an outlet. It acts both as safety and pressure setting valve. $\endgroup$
    – Gert
    Commented Oct 2, 2015 at 14:40
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    $\begingroup$ I've more seen spring loaded ones, but both designs are used in more official pressure relief valves as well... $\endgroup$
    – Jon Custer
    Commented Oct 2, 2015 at 14:43

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