Understanding the physics behind cooking a tadka Premium

Exotic cooking, oil molecules, and seed explosions - the physics behind the art of tadka in Indian cuisine.

Cooking is often called an art, and just like art can be incomprehensible at times, so can exotic cooking be inedible. But that just says more about the audience (or the designated eater) than the painter (or the cook).

At least, this is what I told myself when, a few years ago, I had invited a few friends over and made a vegetable curry that they simply refused to eat.

They said a curry couldn’t really be a curry if its tadka had been cooked in water rather than in oil. In my defence, I had realised quite late that I’d run out of oil in my kitchen. There was nothing other than water around and I’d chopped the vegetables as well.

I was vociferous that water was healthier than oil for the body but eventually I had to concede: my curry wasn’t the curry. But I remain curious, too. Why does one have to use oil to cook the tadka?

In most Indian curry preparations, the tadka is the first step: in a bit of heated oil, the cook puts either cumin (jeera) or mustard seeds. A series of sharp chirps sound, the cook proceeds to add the vegetables and launch into the preparation. In these first few seconds, the flavours of the aromatic seeds seep into the food.

Now, oil and ghee are funny liquids. When you spill some oil, it moves quite slowly, unlike water, which instead moves faster. Place a few drops of oil in a cup of water and it floats. This is unusual: honey or even dishwasher liquid move slowly on a surface but they are also denser than water. How can oil be both sluggish and lighter? The answer lies with oil’s molecules. Oil is made of long chains of large molecules that spiral and stick to each other — not unlike a bunch of noodles or earphone wires. That makes oil a sluggish mover and also hard to separate. These noodle-like molecules of oil render it another important property: a high boiling point.

The boiling point of any liquid is the temperature at which the liquid becomes gas. It’s a common sight when we heat water on the stove: even on a high flame, a pot of water takes some time to turn to vapour. Water (at room temperature and pressure) has a boiling point of around 100º C.