The pressure cooker occupies a place in Indian kitchens that no single appliance holds in most other cuisines. Its dominance follows from what Indian staples require rather than from convenience alone.
What sealing the pot actually changes
Water boils when its vapour pressure matches the pressure above it, so trapping steam raises the pressure and with it the temperature at which boiling occurs. The contents then cook above the temperature an open pot can reach.
A modest rise in temperature produces a disproportionate speed increase, because the chemical reactions that soften food accelerate sharply with heat. Cooking times for dense ingredients fall to a fraction of what they were.
The weight or spring valve is what maintains that pressure, venting excess steam so the interior settles at a stable operating point rather than climbing indefinitely.
Why Indian staples benefit most
Whole pulses, chickpeas and dried beans all take hours in an open pot, because water must penetrate a dense seed and starch must fully hydrate before the texture changes. Higher temperature drives both processes much faster.
Tough cuts of meat cooked on the bone follow the same pattern, since collagen conversion into gelatin is strongly temperature dependent and dominates the time required.
A cuisine built on these ingredients therefore gains far more from pressure cooking than one built on quick-cooking proteins and vegetables.
The fuel argument that made it spread
Cutting cooking time cuts fuel use, which mattered a great deal in kitchens running on bottled gas or on solid fuel bought by weight.
The saving compounds because the pot needs full heat only until pressure is reached, after which the flame can drop to whatever maintains it. Most of the cooking happens on a low burner.
That economics is a large part of why the appliance moved from a novelty to a fixture within a generation across households of very different means.
What the cook gives up
A sealed pot cannot be tasted, stirred or adjusted, so the cook commits to a judgement made before cooking starts and finds out whether it was right afterwards.
The margin between properly cooked and collapsed is also narrow at high temperature, and a pulse taken two whistles too far will not come back.
Volatile aromatics are lost through the vent as well, which is why many recipes add the tempering after pressure cooking rather than before.
Why the whistle became the unit of measure
Indian recipes count whistles rather than minutes, which works because each whistle marks a release of pressure at a known operating point.
It is a rough measure, since burner strength and the quantity of liquid both change how often the valve lifts, but it is consistent within one kitchen using one cooker.
Electric multi-cookers replace it with timed programmes, which is more transferable between kitchens but removes the audible feedback cooks had learned to read.