Cooking in a sealed vessel where trapped steam raises the pressure, and with it the temperature at which water boils.
Technique at a glance
A compact visual model of the lesson. Use the full mechanism and success criteria below when you practice.
Concept
Cooking in a sealed vessel where trapped steam raises the pressure, and with it the temperature at which water boils.
What changes
Water boils at 100°C because that is where its vapour pressure matches the air above it.
What good looks like
Timing starts when full pressure is reached, not when the lid goes on — the come-up can be ten minutes on a full pot.
Practice counts when you cook
Reading this brief does not change your School state. Finish a real practice dish in Cook mode and log the cook; that cook is the evidence that advances the skill.
What to focus on
Mechanism
Water boils at 100°C because that is where its vapour pressure matches the air above it. Seal the vessel and the escaping steam raises that pressure — at roughly one atmosphere above ambient, water boils at about 121°C instead. That twenty-one degree difference is large in chemical terms: reaction rates roughly double for every ten degrees, so collagen conversion and starch gelatinisation run several times faster, and dried beans that would take two hours take twenty-five minutes. The trade is that browning is impossible inside — the environment is saturated with water, so no surface can exceed 100°C and Maillard reactions cannot proceed. Everything that needs browning has to be seared before sealing. Nothing reduces either, since no steam escapes, so recipes use markedly less liquid than their conventional equivalents.
Success criteria
Timing starts when full pressure is reached, not when the lid goes on — the come-up can be ten minutes on a full pot.
A steady quiet hiss or a gently rocking weight means it is holding pressure; loud continuous jetting means the heat is too high.
Natural release takes ten to twenty minutes and continues cooking; quick release stops it immediately, and the choice is part of the recipe.
The lid should not open at all until the pressure has genuinely dropped.
Failure guards
Food is overcooked to mush.
Conventional timings used, or natural release on something already done. Cooking continues through the release, and at these temperatures a few minutes is a lot.
Watery, thin sauce.
Conventional liquid quantities. Nothing evaporates in a sealed vessel, so a recipe adapted from a stovetop stew ends up flooded.
It never came to pressure.
A bad seal, insufficient liquid, or a blocked valve. There must be enough liquid to generate steam in the first place.
Choose a practice dish
This lesson has no authored practice dish yet. Study the success criteria, then choose a recipe that uses the technique from the main skill page.