ASTA Colour & SHU Explained¶
TL;DR — Paprika and chilli are specified by two independent numbers: ASTA colour value (colour) and Scoville Heat Units (heat). They measure different things, with different chemistry behind them — a chilli can be high-colour and mild, or pale and ferociously hot. Specify both, never one as a proxy for the other.
What ASTA Colour Value Measures¶
The ASTA colour value quantifies how much extractable red colour a paprika or chilli contains. It is the standard way to buy paprika, because paprika's primary job in food is natural red colouring.
| Product | Typical ASTA |
|---|---|
| Sweet paprika (Xinjiang sweet pepper) | 8–18 |
| Sweet paprika (overall supply range) | 60–240 |
The colour itself comes from carotenoid pigments in the fruit. Higher ASTA means more of that extractable red — and therefore stronger colouring power. A buyer specifying paprika should always state the target ASTA, because it directly drives both price and how much paprika is needed to hit a target colour in the finished product.
What Scoville Heat Units Measure¶
SHU measures heat — specifically the concentration of capsaicinoids, the compounds that make chilli "hot". The principal one is capsaicin (C16H27NO3).
| Heat level | SHU range | Varieties |
|---|---|---|
| Sweet / low heat | <500 – 10,000 | Xinjiang sweet pepper, Yidu red, Wangdu |
| Medium heat | 10,000 – 20,000 | Xian pepper, Jinta, Erjingtiao |
| High heat | 20,000 – 50,000 | Sanying, Zidantou, New Generation, Seven-Star |
| Extra hot | >50,000 | Jixin, Xiaomi, Chilli King, Shuan Shuan |
Where the Heat Lives: Capsaicin's Address¶
Capsaicin is not evenly spread through the fruit. It is concentrated in the placenta — the pithy tissue around the seeds — and in the surrounding membranes, with some in the skin-surface cells. The seeds themselves contain almost none.
This is a practical point, not a chemistry footnote:
- De-seeding removes the seeds but only slightly reduces heat, because the heat was never in the seeds.
- Removing the placenta and membranes reduces heat substantially.
That is why chilli heat is controlled primarily by variety and placenta content — and why the same variety can be processed to different heat grades. See chilli heat perception for how this maps to the eating experience.
Why You Specify Both¶
The key insight for buyers: colour and heat are independent, chemically and commercially.
- A sweet pepper is high-colour and low-heat — ideal for colouring without adding heat.
- A small hot chilli (like Sanying) is high-heat and low-colour — ideal for adding heat without much colour.
This is why paprika (colour) and chilli powder (heat) are different products, and why the specification sheet lists ASTA and SHU as separate fields. See the buying guide for how they map to product forms.
A Note on Colour Stability¶
Colour is not static — it changes in storage:
- Chilli powder lightens gradually at room temperature, and faster after high-temperature sterilisation.
- Sweet paprika powder may darken after sterilisation.
This is normal colour chemistry. For shelf-stable colour, confirm storage and sterilisation conditions with your supplier. See colour change & storage for the full picture.
References¶
Related¶
Find the Right Product¶
Need a matched colour or heat specification? Browse the paprika powder or contact us.
Frequently Asked Questions
What is the ASTA colour value?
The ASTA colour value measures the extractable red colour of paprika and chilli. It is the industry standard for specifying colouring power — higher ASTA means more red colour. Paprika is commonly specified from 60 to 240 ASTA.
What are Scoville Heat Units (SHU)?
SHU measures the heat (capsaicin content) of chillies. Chinese chilli varieties range from under 500 SHU for sweet peppers to over 50,000 SHU for extra-hot varieties. SHU tells you how hot a chilli or chilli powder is.
Are ASTA and SHU the same thing?
No. ASTA measures colour; SHU measures heat. A chilli can be high-colour and low-heat (paprika) or low-colour and high-heat (small hot chillies). Always specify both independently.
What is the chemical behind chilli heat?
Capsaicin (C16H27NO3) is the compound that makes chilli hot. It is concentrated in the placenta — the tissue around the seeds — and the surrounding membranes, not in the seeds themselves.
What ASTA value do I need for food colouring?
For natural red food colouring, sweet paprika with a higher ASTA (8–18 for Xinjiang sweet pepper, or higher grades) is standard. Confirm your target colour value against your product.
What SHU do I need for a hot sauce?
High-heat varieties (20,000–50,000 SHU) such as Sanying or Zidantou are typical for hot sauces; extra-hot varieties (over 50,000 SHU) for extreme heat. Match SHU to your target heat profile.