The Rajma That Defeated My Grandmother

My grandmother had cooked rajma for fifty-one years and had never once been defeated by it, so when the pot in the guesthouse kitchen in Leh was still full of hard, pale beans after two hours, she took it personally.

“The gas is weak,” she said. The gas was not weak. The flame was a steady blue and the water had been rolling at a full boil since lunch. My father suggested the beans were old. My mother suggested we eat the rice by itself. My grandmother suggested, without saying anything at all, that none of us should speak again.

I put my hand near the side of the pot, which you are not supposed to do, and then over the steam, which you are definitely not supposed to do, and snatched it back at once. It was still hot enough to hurt, but it didn’t feel quite like the furious, skin-stripping hot of the steam that comes off the pot at home in Mumbai. I had a cheap thermometer in my bag from a school project I’d forgotten to hand in, so I clipped it to the side of the pot and waited. It climbed, slowed, and stopped at eighty-eight.

“It’s broken,” my father said. I put it in a mug of tea that had been sitting out, and it read sixty-something, which seemed right. I put it back in the boiling water. Eighty-eight. The water was boiling, properly boiling, at twelve degrees below the temperature every textbook I owned had told me water boiled at.

That night I lay awake in a room that smelled of kerosene and read about it on a phone with one bar of signal. Water doesn’t boil at a hundred degrees. At any temperature, the fastest molecules at the surface of hot water are escaping into the air as vapour, and that escaping vapour pushes outwards, a push called vapour pressure. The hotter the water, the more molecules have the energy to break free, and the harder the push. Boiling is the moment that push becomes strong enough to match the weight of the air pressing down on the water. Then bubbles of vapour can form inside the water itself, not just at the surface, and hold their shape against the air above.

At sea level that balance comes at a hundred degrees. Leh sits about three and a half kilometres up, where there is roughly a third less air above you, so the air presses down less hard and the water reaches the balance sooner, at around eighty-eight. After that, extra heat just makes it boil harder. Every bit of energy the flame adds goes into tearing more molecules loose as steam, and none is left over to raise the temperature. A bigger flame makes more bubbles, not hotter water.

And rajma doesn’t care how hard the water is bubbling. It cares about the temperature. The starches inside each bean need to soak up water and swell, and the pectin cementing its cells together needs to break down, and those are chemical changes that speed up or slow down with heat. A rough rule for reactions like these is that every ten degrees cooler makes them about half as fast. Twelve degrees cooler, and the same beans could easily need more than twice as long, which is exactly what we were watching. The beans weren’t old and the gas wasn’t weak. We were cooking in water that was, by the standards of a kidney bean, lukewarm.

In the morning I explained all of this to my grandmother, at length, with a diagram on the back of a bus ticket. She listened to every word. Then she went to the guesthouse owner, borrowed his pressure cooker, and had the rajma done in forty minutes.

I had always thought of the pressure cooker as a machine for impatient people. It isn’t. It’s a machine for changing the weather inside a pot. When you seal the lid, the steam has nowhere to go, the pressure inside rises, and the water has to get much hotter before it can boil. The whistle is the moment the pressure gets high enough to lift the weight on the lid and let a little steam out, which is why it keeps the inside at a steady, higher pressure rather than letting it climb forever. Every whistle I’d ever heard from our kitchen at home was the sound of water being forced past a hundred degrees.

“You knew,” I said to her, while she served the rajma. “You knew it would work.”

“I knew the man had a cooker,” she said. “Up here, everyone has a cooker.” Which, I realised, was the same explanation as mine, just without the bus ticket.