Chilli SHU and ASTA Colour Explained

Scoville Heat Units (SHU) measure the pungency of chilli, based on the concentration of capsaicinoids, the compounds behind the heat sensation. A higher SHU means a hotter chilli.

The original Scoville method used a human taste panel and repeated dilution. It has largely been replaced by HPLC (high-performance liquid chromatography), which measures capsaicinoid concentration directly and converts it to an SHU-equivalent figure. HPLC results are generally more consistent and repeatable than a taste panel.

ASTA colour value is a standardised method, developed by the American Spice Trade Association, for measuring the extractable red colour of chilli and paprika, expressed as a number. A higher value generally means a more intense red colour extract.

Buyers sourcing for colour-sensitive uses, such as oleoresin extraction, food colouring, or products where appearance sells, commonly specify a minimum ASTA value.

Colour and heat do not move together. A chilli can be high in colour and moderate in heat, or the reverse, so a high ASTA value does not mean a hotter chilli and a high SHU does not mean a redder one.

If both matter to your product, specify each separately and do not let a supplier answer one with the other. Our Guntur sourcing guide and our Teja guides show how colour and heat figures are read for those varieties.

• Ask for SHU as a range, with a minimum and a maximum, not a single number. Pungency varies by variety, growing conditions and even within one harvest.
• Ask for ASTA as a minimum value, or a range if your product is sensitive to over-colour.
• State which lab and method will be used to verify each, and which sample it is drawn from.
• Say whether the figure applies to the whole or ground chilli as supplied, or to a downstream product such as an oleoresin, since these are measured differently.
• Do not rely on a variety name in place of a tested figure. Two lots of the same variety can test differently.

Ask for both figures on the actual lot, on a Certificate of Analysis, before shipment. That way a later dispute is about a number in a report rather than about a description. Our certificate of analysis guide covers what to check on the report itself.