Rescues · TO PRESSURE COOK
It never came to pressure.
Why it happens
A bad seal, insufficient liquid, or a blocked valve. There must be enough liquid to generate steam in the first place.
Recovering it
Undercooked is easy — reseal and give it a few more minutes. Overcooked is not recoverable and is the characteristic failure of this tool, so err short and check. A watery sauce is fixed by removing the lid and reducing on the hob afterwards, which most pressure cookers allow directly. If it will not come to pressure, check the gasket and the vent before anything else.
The 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.
The full TO PRESSURE COOK lesson — how to tell, where to practise it, what it carries to.