ASTA Colour vs SHU Heat: What's the Difference
ASTA and SHU are the two numbers on every chilli specification — and they measure completely different things. ASTA is colour, SHU is heat, and neither predicts the other. This comparison explains both.
At a Glance
- ASTA
- Colour (capsanthin), 460 nm
- SHU
- Heat (capsaicinoids), HPLC
- Relationship
- Independent
- Proof
- A paprika can be high-ASTA and zero-heat
The core difference
| Dimension | ASTA colour value | SHU heat |
|---|---|---|
| Measures | Colour — extractable carotenoids, chiefly capsanthin | Heat — capsaicinoid concentration |
| Method | Spectrophotometry at 460 nm (ASTA Method 20.1) | HPLC, converted to SHU (≈1 ppm capsaicin ≈ 16 SHU) |
| Controlled | Independently | Independently |
| Stability | Degrades under oxygen, light and heat | Varies ±40% with growing conditions |
Why the choice matters
A lot of mis-bought chilli comes from treating the two numbers as one property. They are not: ASTA is colour, SHU is heat, and they are controlled independently — a paprika can be high-ASTA and zero-heat. The full technical background is on the ASTA colour value and SHU explained pages.
How to specify both
Specify the ASTA target for colour and the SHU window for heat as separate lines in the specification — plus the variety and mesh. Carotenoids degrade under oxygen, light and heat, so colour fades with age; fresh lot turnover protects the ASTA you bought.
How to specify
Write both numbers into the specification: ASTA for colour, SHU window for heat, plus variety and mesh. Confirm your exact targets when you inquire.
Heat and colour values are representative. Confirm your exact SHU window, ASTA, form and mesh when you inquire.
Frequently Asked Questions
What is the difference between ASTA and SHU?
ASTA measures colour — the extractable carotenoid pigments such as capsanthin that give paprika its red colour. SHU measures heat — the capsaicinoids that trigger the burn. They are separate properties, controlled independently.
Can a chilli be high-ASTA and zero-heat?
Yes. ASTA and SHU are independent — a paprika can be high-ASTA and zero-heat, which is exactly what sweet paprika is.
Which should I specify first?
Both, as separate lines: ASTA for colour, SHU window for heat. Neither predicts the other, so a specification with only one number leaves the other uncontrolled.