The Scoville scale measures chilli heat in Scoville heat units. It began in 1912 as a dilution taste test; today the capsaicinoids are measured by HPLC and converted to the same units.
What it is¶
The Scoville scale ranks the pungency of chillies and chilli products. A number in Scoville heat units (SHU) says, in effect, how many times an extract must be diluted before its heat can no longer be detected. A sweet bell pepper scores zero; a jalapeno a few thousand; a habanero a few hundred thousand; pure capsaicin about sixteen million.
The scale is logarithmic in spirit though not in form: the difference between 2,000 and 20,000 SHU is dramatic, the difference between 1,500,000 and 1,600,000 hard for anyone to feel.
Scoville's test¶
Wilbur L. Scoville was an American pharmacist working for the drug company Parke-Davis, which used capsaicin in a warming ointment and needed a way to standardise its chillies. In 1912 he published what he called an organoleptic test — one that relies on the human senses.
An exact weight of dried chilli was steeped in alcohol overnight to extract the capsaicinoids. The extract was then diluted in sugar water and given to a panel of five tasters. Dilution continued step by step until a majority of the panel (three of five) could no longer detect any heat. The dilution factor at that point was the rating: a chilli whose extract had to be diluted 5,000 times was 5,000 units.
🔬 Why the taste test fell out of use
Human tasters were the weak point. Sensitivity varies from person to person and falls quickly with repeated exposure, so a panel tasting several samples in a session becomes less reliable as it goes. Results varied between laboratories by a wide margin, and the test could not tell capsaicin from other pungent substances.
The modern method: HPLC¶
Since the 1980s, laboratories have measured pungency by high-performance liquid chromatography (HPLC). A chilli extract is pumped through a column that separates its components; a detector measures how much of each capsaicinoid is present, usually in parts per million of dry weight.
The results are often given in ASTA pungency units (from the American Spice Trade Association) and converted to Scoville units by multiplying by a factor of about 15 — the conversion used in the trade, though it is an approximation. Some methods weight each capsaicinoid by its relative pungency: capsaicin and dihydrocapsaicin count fully, the minor ones rather less.
HPLC is objective and repeatable, but it measures chemistry, not experience. Two chillies with the same rating can feel quite different: some capsaicinoid mixes hit the back of the throat at once, others build slowly on the tongue, and sugar, acid and aroma all change how heat is perceived.
Typical values¶
Heat varies widely with variety, growing conditions and even the position of a fruit on the plant, so every figure below is a range. Record claims for individual varieties are covered in hottest-chilli-records.
| Chilli or substance | Approximate SHU |
|---|---|
| Bell pepper | 0 |
| Sweet paprika | 0–1,000 |
| Padrón and shishito | 0–2,500 (most mild, occasional hot one) |
| Poblano | 1,000–2,000 |
| Espelette | Up to about 4,000 |
| Jalapeño | 2,500–8,000 |
| Aleppo pepper | Roughly 10,000 |
| Serrano | 10,000–23,000 |
| Cayenne | 30,000–50,000 |
| Bird's eye | 50,000–100,000 |
| Habanero and scotch-bonnet | 100,000–350,000 |
| Ghost pepper (bhut jolokia) | Roughly 850,000–1,000,000+ |
| Carolina Reaper | Roughly 1,400,000–2,200,000 |
| Pure piperine | Roughly 100,000 |
| Pure capsaicin | About 16,000,000 |
Pepper sprays used by police are also rated in Scoville units, typically in the millions, though their labelling is not standardised.
💡 Reading the numbers
A quoted range tells you more than a single figure. A jalapeño bought in a British supermarket is often at the bottom of its range; one grown hot and dry can be at the top. Taste a sliver before adding a whole chilli to a dish.
Limits of the scale¶
The scale measures only capsaicinoids. It says nothing about the heat of black-pepper (piperine), mustard, horseradish or wasabi (all mustard-oils), or ginger (gingerols and shogaols), which act on overlapping but different receptors and feel different in the mouth. Scoville figures for these substances, where quoted, compare pure compounds rather than foods.
It also measures a concentration, not a dose. A single drop of 1,000,000 SHU sauce spread through a large pot of chilli can make a milder dish than a spoonful of cayenne. Heat perception also depends on the eater: regular chilli users genuinely feel less burn (see spice-tolerance).