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I dined with a famous computer scientist a few days ago. My first column of 2015 is on something he suggested I write about. Some esoteric computer science or mathematical concept that we touched on, maybe?

Not quite. We were discussing how spicy the chhole, dum aloo and baingan bharta that we ordered were.

Our friendly waitress had asked us to choose our spice level on a scale of 1 to 5, with 5 being—in her words—“really, really hot!" We settled for 2. The result was, at least to my taste buds, pretty bland. We got talking about that, and I remembered a young woman who challenged me years ago to chomp a tiny yellow chilli, which I did, and the restaurant nearly called the fire department. I was that close to spontaneous combustion.

So the computer scientist suggested I write about spiciness. How do you measure how hot a given spice is, without having to use the ultra-technical term “really, really hot"?

Turns out there is actually a scale for this, and various notorious chillies have been ranked on it.

Apologies if this is old hat for you because it was news to me. Any given spice can be measured for how many Scoville Heat Units (SHU) it has, and that will place it somewhere on the Scoville Heat Scale. To give you an idea, the basic green pepper—capsicum, or simla mirch in India—is at the bottom of the scale, at 0. Jalapeño peppers—hot stuff, I think you’ll agree?—rank somewhere between 2,500 and 5,000 SHU. There’s more, but let me first tell you about what’s really interesting here: how this scale came about.

Wilbur L. Scoville, a chemist at the Parke-Davis company, devised the scale in 1912.

His Scoville Organoleptic Test went like this: take an extract of pure chilli that you want to evaluate. Dilute it with a certain quantity of water and give it to a panel of testers to see if it burns their mouths. If it does, dilute the solution and try again.

When the testers can no longer detect the spice, stop.

The ratio between the quantity of water needed to blank out the chilli taste, and the quantity of chilli, gives you the SHUs.

So if a jalapeño is rated at 2,500 SHU, a teaspoon of mashed jalapeño would need to be mixed into 2,500 teaspoons of water to become unnoticeable to Scoville’s testers. Think of what that means. A teaspoon is about 5ml. So the jalapeño’s Scoville rating means that you’d have to dunk that single teaspoon in about 12.5 litres of water—about a full bucket’s worth—to completely drown its sharpness.

Gives you some idea of that sharpness, I bet.

And this is how you judge how potent a chilli is: by measuring what it takes to blunt its potency.

If that notion of blunting seems like a novel idea, it really isn’t.

It’s at the heart of a lot of different ways to measure things. It’s as if you decided to measure the speed of a plane by flying another plane alongside it. When you are flying fast enough that the first plane seems stationary—its speed relative to you reduced to zero—look at your speedometer (planes have speedometers, I’m presuming).

You’ll know its speed.

Your vegetable vendor measures the weight of your tomatoes by putting them on one pan of a weighing balance and adding weights to the other until both pans are balanced. That is, until the tomatoes appear to weigh nothing, relatively.

Or think of how the Olympic Games figure out who the strongest man in the world is. They give several contenders heavier and heavier loads to lift until all but one have reached their limits—their ability to lift more, in a sense, blunted. It’s called weightlifting.

In effect, Scoville’s method for measuring spiciness is no different from any of these.

But as you can imagine, his method had one major problem. It relied on the subjective impressions of his testers. After all, you might have a keener tongue than mine, and thus be able to detect much fainter traces of jalapeño than I can, and so you’d give it more SHUs than I would. This is why Scoville used a panel of testers. Even so, it’s a worryingly inexact scheme, at least for those among us who care about how spicy chillies really are.

So today, scientists use liquid chromatography to determine how much capsaicin a given chilli has. That’s the active ingredient in them that causes that burning sensation in your mouth. They then translate that quantity back to SHUs, preserving the century-old Scoville Heat Scale.

So if you think jalapeños are hot, you should take a look at that scale.

There’s a Bhut Jolokia from Nagaland that’s at over 1 million SHUs. There’s a Carolina Reaper that’s at 2.2 million SHUs.

That last number corresponds to about a 1,000 buckets of water.

About what I felt I needed, when I chewed on that little yellow firestorm.

Once a computer scientist, Dilip D’Souza now lives in Mumbai and writes for his dinners. A Matter of Numbers will explore the joy of mathematics, with occasional forays into other sciences.

Comments are welcome at dilip@livemint.com. To read Dilip D’Souza’s previous columns, go to www.livemint.com/dilipdsouza