Chilli Heat Guide (Scoville Scale)
Scoville Heat Units (SHU) measure the concentration of capsaicin — the compound that causes the burning sensation when you eat a chilli.
What Scoville units measure
The Scoville scale was developed by pharmacist Wilbur Scoville in 1912. Originally, it measured how much sugar water was needed to dilute a chilli extract until heat was no longer detectable. Modern testing uses high-performance liquid chromatography (HPLC) to measure capsaicin concentration directly.
Capsaicin is concentrated in the placenta — the white pith inside the chilli — not the flesh or the seeds (though seeds often absorb capsaicin from contact with the placenta). Removing the pith significantly reduces heat.
Heat bands
Mild
0–2,500 SHU
Bell pepper (0 SHU), Poblano (1,000–2,000 SHU), Anaheim (500–2,500 SHU)
Little to no perceptible heat. Suitable for everyone, including children.
Medium
2,500–50,000 SHU
Jalapeño (2,500–8,000 SHU), Serrano (10,000–23,000 SHU), Cayenne (30,000–50,000 SHU)
Noticeable warmth to moderate heat. Widely used in sauces, salsas, and cooking.
Hot
50,000–200,000 SHU
Tabasco (30,000–50,000 SHU), Thai bird's eye (50,000–100,000 SHU)
Significant heat that builds quickly. Requires care when cooking — handle with gloves.
Very hot
200,000–1,000,000 SHU
Habanero (100,000–350,000 SHU), Scotch bonnet (100,000–350,000 SHU)
Intense, lingering heat. Small amounts transform a dish. Wear gloves when cutting and avoid touching your eyes.
Superhot
1,000,000+ SHU
Trinidad Moruga Scorpion (1,200,000+ SHU), Carolina Reaper (1,400,000–2,200,000 SHU)
Extreme heat capable of causing physical distress. Handle with gloves and eye protection. Not suitable for casual use.
Factors that affect heat
SHU figures for a variety are ranges, not fixed values. The same variety can produce significantly hotter or milder fruits depending on growing conditions:
- •Water stress: restricting water as fruits mature increases capsaicin production. Many growers do this intentionally in the final weeks before harvest.
- •Heat stress: higher temperatures during fruiting generally increase heat levels, which is why UK-grown chillies are often milder than the same variety grown in a warmer climate.
- •Genetics: seed strain matters — a supermarket jalapeño seed will not produce the same heat as a selected strain bred for heat.
- •Growing conditions: more light and warmth during fruit development typically increases heat concentration.
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