What is “spicy”?
When someone says that something tastes spicy, it’s slightly incorrect. Spiciness is not a flavor, but rather a pain reaction sent to your brain from polymodal nociceptors in your throat, mouth, and tongue. These receptors are triggered by a group of compounds found in chili peppers called capsainoids. When the receptors detect capsaicin, they send a signal to your brain that triggers a fight-or-flight response, which leads to sweating and an increased heart rate. Your brain literally thinks your mouth is on fire.
Not all capsaicinoids are created equal, however. Alkylamides in black pepper and chili cause a strong burning sensation in the mouth due to the heavier weight of the molecules, while foods like wasabi, mustard, and horseradish contain lighter molecules known as isothiocyanates. These smaller molecules can easily be aerosolized into your sinuses, creating a burning sensation in your nose.
Okay, so different foods – and especially chilies – have different levels of spiciness, and they can vary dramatically in how the heat affects you. Is there a way to scientifically measure the spiciness of chilies so we can stay within the desired pain range?
The origin of Scoville
The Scoville sensory test, or more commonly the Scoville scale, was created by Wilbur Lincoln Scoville at the Parke-Davis pharmaceutical company in 1912 when he tested the heat levels of various chili peppers. Scoville had to create a system in which he could reliably measure the perceived capsaicin content of peppers for use in a pharmaceutical environment.
The Scoville scale has become the standard way to measure the heat of food – and especially chili peppers. This scale aims to help spicy food lovers understand exactly what they’re getting into when they bite into a fearsome chili pepper.
How does the Scoville scale work?
- Scoville Heat Units (SHU): The spiciness of a chili is measured in units known as Scoville Heat Units or SHU.
- Testing Methods: There are two primary methods for testing the capsaicin content in chili peppers: the Scoville scale and High-Performance Liquid Chromatography (HPLC).
SHU is an abbreviation for Scoville Heat Units, the units used to measure the “spiciness” of a chili. When used on the scale, SHU starts at 0 SHU and increases indefinitely.
To calculate the SHU of a chili, a sample is dehydrated and dissolved in alcohol to extract the capsaicinoids, then diluted in sugar water. The concentration is repeatedly diluted in increasing amounts of sugar water until a trained tasting panel can no longer detect the heat in the solution. The final SHU level is then determined based on the number of dilutions required to reach this terminal level and is classified in increments of 100 SHU.
Popular Chilies and Their Scoville Ratings
All of these numbers can make your head spin without context based on real-life experience. While maybe not all of us have eaten Ghost Pepper by itself, most of us have eaten bell pepper, Jalapeño, and perhaps even raw Habanero. Here are examples of where common chili varieties fall on the Scoville scale.
- Mild Pepper:
- SHU Range: 0 – 500 SHU.
- Examples: Bell pepper, sweet pepper.
- Mildly Spicy Chili:
- SHU Range: 2,500 – 25,000 SHU.
- Examples: Jalapeño, Serrano, Fresno.
- Medium Spicy Chili:
- SHU Range: 30,000 – 100,000 SHU.
- Examples: Cayenne, Thai chili.
- Hot Chili:
- SHU Range: 100,000 – 500,000 SHU.
- Examples: Habanero, Red Savina, Scotch Bonnet.
- Super Hot Chili:
- SHU Range: 500,000 – 2,000,000+ SHU.
- Examples: Ghost Pepper, Scorpion Pepper, Carolina Reaper.
Pepper X is a variety grown by chili grower Ed Currie, who also created the Carolina Reaper. In 2023, Guinness World Records awarded Ed the title of the world’s hottest chili with the new Pepper X, which scored 2.69 million SHU. There is some debate over the validity of this claim due to testing methods and grower policies. Undoubtedly, a new king will rise to take this crown at some point in the future. Currently, Pepper X is featured on Hot Ones in The Heatonist and Ed Currie’s The Last Dab: Xperience series.
Alternative method for measuring spiciness
High-Performance Liquid Chromatography (HPLC), which has been applied using the Gillett method since the 1970s, has become the modern standard for measuring the spiciness of chili peppers. This technique quantitatively analyzes capsaicinoids by measuring their concentration in parts per million (ppm). The results are typically reported in units used by the American Spice Trade Association (ASTA), which can be converted to Scoville Heat Units (SHU) using a mathematical conversion factor, typically around 15. HPLC is valued for its accuracy and efficiency in identifying and quantifying capsaicinoids, which includes not only capsaicin but also dihydrocapsaicin.
To determine spiciness, HPLC traces the peak areas of capsaicin and dihydrocapsaicin in a dry sample dissolved in acetonitrile. The heat in parts per million (ppmH) is calculated by summing the area of the capsaicin peak and 0.82 times the area of the dihydrocapsaicin peak, then dividing by the area of the standard capsaicin sample peak. The resulting ppmH value is then multiplied by 15 to obtain the SHU (Scoville Heat Units).
Example Calculation
Assume the following data from HPLC analysis:
- Capsaicin peak area = 5000
- Dihydrocapsaicin peak area = 3000
- Standard peak area = 1000
First calculate ppmH:
Then convert ppmH to SHU:
Therefore, the sample would be reported as 111.9 Scoville Heat Units (SHU).
Although this method is more accurate than the traditional Scoville organoleptic test, experts note that it tends to produce results that are about 20-40% lower than the original test. Despite its accuracy, the HPLC method primarily focuses on the main capsaicinoids and may overlook other spicy compounds that can also contribute to the overall heat of the chili.
