How is the heat level of a chilli pepper determined?

by House of Scoville
October 09, 2017

For those of you that don’t already know (or curious to understand the meaning behind our company name), there is a measurement unit, known as the Scoville scale, that measures peppers on an incremental scale. The scale goes up to 16,000,000 units, with 16 million being the heat level of pure capsaicin, the spicy compound in chilli peppers. What most people - even many of the most dedicated chilli heads - don’t know, is how exactly a pepper’s place on the scale is determined.

Spicy Omelette

How did the Scoville scale come to be?

The scale is quite simple in origin, actually. It was named after William Scoville, who created something known as the Scoville Ornographic test. This test evaluated the amount of capsaicin that is present in a hot chilli pepper. The scale measures this value in Scovilles, which could inform people how spicy a hot chilli pepper  was.

How does the Scoville scale work?

Surprisingly, the Scoville scale itself is actually fairly simple, as far as scientific processes go. It’s also not as entirely accurate as a chilli head might hope, due to the way the test is conducted.

First, you must perform an organoleptic test. To do this, you take an extract of the capsaicin that’s contained in a dried chilli pepper. This is then mixed into a solution of water and sugar. Use enough so that you can barely taste the heat content of the capsaicin. Then, taste the capsaicin (a panel of taste experts is usually employed to do this, hence the imperfect accuracy of the experiment’s design) until you can ‘barely detect the heat.’

To discover the unit’s Scoville rating, you must observe how many times you diluted the oil before you couldn’t detect the spice anymore. For example, a jalapeno that had to be diluted 5,000 times would rank 5,000 Scoville units.

In an attempt to preserve some consistency, the tasters only take one sample per session, so spice from a previous entry doesn’t affect the next.

However, depending on the age of the jalapeno, the tasters’ sensitivity to heat, and other factors involved in the pepper’s origin and growing conditions, different people may arrive at different values. A Scoville rating for a pepper may vary by tens of thousands of Scoville units.

Fortunate, then, that the scale goes up to 16 million. Also, with the advent of internet reporting and research, some of these ratings could be a result of improper information spreading. You can still get the general idea of how hot a pepper will be.

Have a look at our Scoville Heat Unit scale to get an idea of the range each chilli pepper ranks in. But generally, jalapenos will rank between 2,500 and 20,000 SHU, habaneros between 100,000 and 350,000 and Bhut Jolokia’s around 800,000 SHU.

Scoville scale applications

The Scoville scale has given us a foundation to analyse the spice content of a lot of peppers. Currently standing as the champion pepper is the Carolina Reaper, bred by a farmer in Carolina simply to cause tongues across the world to hate their owners. It stands at a whopping 2.2 million. The runner-up is the Trinidad Moruga Scorpion pepper, at 1.6 million Scovilles.

These peppers are both incredibly potent, but still pale in comparison to pure capsaicin. A Bhut Jolokia pepper would be composed of about 10% capsaicin, because the pure oil stands at 16 million Scoville units.

The Scoville scale has also been used to measure the heat level of other foods that don’t contain capsaicin. For example, it can measure the piperine content that gives black pepper its kick. It can measure the gingerol content of different gingers, and probably the content of the spicy ingredient in wasabi and horseradish.

The Scale has also found a compound that blew past the 16 million mark that pure capsaicin is rated at. This stuff is known as resiniferatoxin, and it’s found in a series of sadistic cactus-like plants that grow in Mexico. It’s a thousand times hotter than capsaicin, coming in at 16 BILLION Scoville Heat Units! It’s hard enough to imagine how hot pure capsaicin would be. This stuff is on a completely different level.

New alternative to the Scoville Heat Unit scale

There’s a new method of determining heat factors of peppers that’s more accurate than using the Scoville scale, though this new method allows for an easy conversion to Scovilles.

This method was pioneered by ASTA - the American Spice Trade Association - and it uses a process known as high-performance liquid chromatography to evaluate the spice content of different food. This process involves a lot more math than the Scoville scale did, requiring that examiners weigh the food and evaluate their capacity to produce heat.

ASTA’s new technique also evaluates heat on several different factors, instead of just the intensity of the heat.

  • How hot the pepper is
  • How long the spice lingers for
  • How fast it comes on
  • Where you sense the heat
  • Whether it registers as flat (a sustained heat that feels like it’s being evenly brushed over your tongue) or sharp (a fast-acting heat that feels like pinpricks)

The result is expressed in ASTA pungency units. These can be multiplied by fifteen to give an approximation in Scovilles. While this method in itself may be much more accurate than the Scoville scale method, the conversion to Scovilles generally results in some discrepancy. The numbers always seem to be off by between 20% and 50%.

Still, perhaps it's time for the industry standard to switch over to ASTA’s more accurate method.

  • There are inconsistencies when using the Scoville scale.
  • It’s hard enough to convert ASTA’s precise measurements into Scoville units.
  • Scoville requires taste testers, who can only handle so much spice in a session. This means that evaluations could take days, and depending on how many tests a person does, their capacity to feel heat will be different.

Plus, when you think about it, there might not always even be people to do Scoville tests. Not every sane person would jump at a job if the description entails sampling peppers so hot that they earn names like “Reaper” and “Scorpion”!

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