What is the Scoville Scale? The Story Behind The Heat

No scale is hotter…

We all know that peppers are hot, but the Scoville scale helps us put a rating to them. That’s the simplest of definitions for the Scoville scale. It’s a heat rating index of hot peppers running from no heat to “oh my god, I’m going to catch on fire scorching” and even beyond.

But let’s dig a little deeper.

What is the Scoville Scale?

The Scoville scale is actually named after its father, Wilber Scoville. A pharmacist by trade (working for Parke-Davis Pharmaceutical Company at the time), Scoville created a simple way to measure the pungency of a hot pepper. The Scoville Organoleptic Test is based on dilution of ground up hot chili peppers. It answers the question: How many equal parts of sugar water do I need to add to a same-sized part of ground chili pepper until I taste no discernible heat at all?

Wilber Scoville had a panel of tasters who took the test, sipping these concoctions of chili pepper and sugar water in multiple-day trials until no heat was noticed. Yes, they performed these sipping trials until they reached a level where their mouths no longer burned from the ground hot pepper within. Aren’t you glad you aren’t this team of tasters?

The equal parts it took to get to that moment became the Scoville heat units (SHU) we see today on the pepper scale. For instance, one cup of ground poblano pepper (SHU 1,500) would take approximately 1,500 cups of water diluted into it to no longer feel any burning sensation in your mouth.

Going high-tech: High performance liquid chromatography

There is now a high tech option out there for deciphering the heat of chili peppers. They don’t require the tasting method that Scoville’s original test needed. And that’s a good thing as some of the hottest peppers in the world these days could really drive those tasters crazy.

Known as high-performance liquid chromatography (or HPLC for short) this test measures the chemical capsaicin in chili peppers which causes the heat in the first place. But in a nostalgic nod to the chili pepper heat measuring pioneer Wilber Scoville, scientists then convert their results back into Scoville units. The simplest way to think of the science is about one part of the chemical capsaicin per one million equals around fifteen total Scoville units.

It’s all subjective: The weaknesses of the pepper scale

While we’ve talked a lot of science here, really the measurement of hot chili pepper heat – especially with the original Scoville scale – is a pretty subjective thing. There are aspects that affect the findings enough that different laboratories would sometimes have widely varying results, sometimes up to 50% different!

  • Human subjectivity: The Scoville Organoleptic Test relies on the variance in people’s taste buds. People have varying degrees of the hotness they can take, meaning results would vary from tester to tester.
  • Where the pepper is grown: Peppers, like other vegetables, take on the flavors of the earth they are grown in. That means, the heat of a certain type of pepper can vary widely based on where in the world it originated.
  • Variance in peppers themselves: Like humans, no two peppers are alike. There can be differences in the heat from pepper to pepper.

Even the HPLC test has questions surrounding its conversion into Scoville Units. Some scientists believe that the conversion tends to position the heat of the peppers on the pepper scale too mildly compared to what a human tester would give.

Experience the heat

But still, for measuring something that varies so much, the Scoville scale is as accurate as we need it to be. It helps us chiliheads out there, both new and old alike, determine the heat of all sorts of foods based on hot peppers, from hot pepper sauces to gourmet Southwestern dishes. So dive into the world of hot peppers and experience the heat for yourself!

UPDATE NOTICE: This post was updated on September 5, 2019 to include new content. It was originally published on June 8, 2013.