Short answer
Both are graded on the colour that can be drawn out of the spice, not on how the powder or threads look. Paprika is extracted into acetone and read at 460 nm to give an ASTA colour value; saffron is steeped in water and read at 440 nm to give the colouring strength used by ISO 3632. Each is a single-wavelength measure of how much carotenoid pigment the spice releases, so it tracks colouring power well and hue poorly, and it falls as the spice ages.
A ground spice is a poor thing to judge by its surface. How red a paprika looks in the jar shifts with how finely it was milled, how much oil is at the surface and the lamp it is seen under, and none of those tells a buyer how much colour it will give a sausage or a paella. So the trade measures what a cook actually uses: the pigment that comes out. A weighed sample is soaked in a solvent that suits the pigment, the solution is diluted, and its absorbance is read at one wavelength near the pigments' absorption peak. The result is scaled to the sample weight, which makes it a statement about colouring power per gram. For paprika that figure is described in the research literature as the main parameter setting quality and market price.
Paprika's colour comes from carotenoids. The orange-to-red xanthophylls capsanthin and capsorubin are the pair that also define paprika extract as a food colour (E160c), and they sit alongside yellow-orange carotenes and other xanthophylls. Carotenoids are fat-soluble, so the American Spice Trade Association's Method 20.1 — titled for extractable colour in capsicums and their oleoresins — uses acetone. In a published laboratory application the powder stands in acetone in the dark for at least 16 hours, the extract is diluted and read at 460 nm in a 1 cm cell, and the ASTA value is the absorbance multiplied by a constant and an instrument correction and divided by the sample weight. The same figure multiplied by 40 gives the IC colour units used for oleoresins. One instrument maker puts commercial paprika standards at roughly 65 to 180 ASTA; the grinds in the study cited here ran from 150 to 200.
Open sources print the constant as 16.4 or 164 depending on how the extract is diluted. The method text is sold and Colourwise has not read it, so this site offers no ASTA calculator.
Saffron is the odd one out among carotenoid spices. Its pigments, the crocins, are crocetin joined to sugars, which makes them dissolve in water — the reason a few threads colour a pan of rice without any fat. The ISO test follows the chemistry: in a laboratory account of ISO 3632-2, saffron is stirred in cold water in the dark for an hour, filtered and diluted, and the absorbance at 440 nm is expressed for a 1% solution in a 1 cm cell on a dry-weight basis. That number is the colouring strength. The same extract is read twice more in the ultraviolet as indicators of picrocrocin, which gives bitterness, and safranal, which gives aroma. ISO 3632-1 then sorts saffron into three categories, and a lot must meet all three readings and a moisture limit to earn one. For the 2011 edition the colouring-strength floor was reported as 120 for the lowest category and 200 for the highest. A 2025 edition has since replaced it and may differ.
Both figures compress a mixture of pigments into one absorbance, and that hides things. In the paprika study, grinds from one origin held about 30% more total carotenoid than those from the other, yet their ASTA values were the same; the authors concluded that a difference of around half is needed before ASTA units move. Nor does one wavelength separate the red xanthophylls from the yellow carotenes, so two paprikas with the same value can differ in hue. For saffron the stakes are higher because of the price, quoted at up to 20,000 euros a kilogram, and the limits are sharper: researchers applying the ISO test report that it cannot reveal some plant adulterants, cannot tell synthetic colour from natural, and estimates safranal poorly. A category on the label is evidence of colouring strength, not proof of authenticity.
Carotenoids are long chains of alternating double bonds, and the same structure that absorbs blue light also reacts with oxygen. Heat, light and moisture speed that up. In an accelerated test, eight hours at 80 °C took paprika from Peru from 198 to 162 ASTA units and paprika from China from 196 to 173, with the second, which held more esterified carotenoids, proving the more stable. The authors list enzymes, microbes, moisture, light and unsuitable temperature as the storage conditions that keep degrading colour after milling. A jar of paprika above a hob is exposed to nearly all of them. Whole dried peppers and saffron threads expose less surface than powder, which is one reason to grind or crush only what is needed.
| Spice | Method | Pigments measured | Solvent | Wavelength | Reported as |
|---|---|---|---|---|---|
| Paprika and other capsicums | ASTA Method 20.1 | Carotenoids, including the red xanthophylls capsanthin and capsorubin | Acetone | 460 nm | ASTA colour units |
| Saffron | ISO 3632-2:2010 (test methods); ISO 3632-1 (specification, current edition 2025) | Crocins, water-soluble glycosyl esters of the carotenoid crocetin | Water | 440 nm | Absorbance of a 1% extract in a 1 cm cell, on a dry-matter basis |
| Origin | Untreated (ASTA units) | Heated (ASTA units) | Change |
|---|---|---|---|
| Peru | 198.1 | 161.9 | −18% |
| China | 196.2 | 172.9 | −12% |
Why: Carotenoids have oxidised, helped by warmth, light and air near the cooker.
Fix: Buy small amounts, keep them in an opaque airtight container away from heat, and replace rather than add more.
Why: The value counts total extractable pigment at one wavelength; hue depends on the balance of red and yellow carotenoids and on the grind.
Fix: Judge hue by warming a pinch in oil, and use the ASTA figure only for strength.
Why: Powder is the form most easily adulterated, and the colour test alone cannot tell added colourants from crocins.
Fix: Buy threads from a seller who states the ISO category and harvest year.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactModerate evidence
ASTA extractable colour for paprika is obtained from an acetone extract read at 460 nm in a 1 cm cell and scaled to the sample weight, and IC colour units are 40 times the ASTA value.
Caveat: Taken from a research paper applying the method and an instrument maker's summary; the ASTA manual is sold and was not read, and the two sources print different scaling constants.
Source: Changes in Carotenoids and Quality Parameters of Sweet Paprika (Capsicum annuum) After an Accelerated Heat Treatment; ASTA Color and IC Color of Paprika and Oleoresin Spices; ASTA Analytical Methods Manual (method listing)
FactStrong evidence
Heating ground sweet paprika at 80 °C for 8 hours lowered mean ASTA colour from 198.1 to 161.9 units in Peruvian samples and from 196.2 to 172.9 in Chinese samples, the latter change not being statistically significant.
Measured: 30 commercial paprika grinds (15 from Peru, 15 from China) from one Spanish supplier. Method: Accelerated heat treatment; ASTA value by acetone extraction at 460 nm
Caveat: An accelerated stress test, not a measurement of fading at room temperature.
FactModerate evidence
Untreated paprika from one origin contained about 30% more total carotenoid than paprika from the other without a corresponding difference in ASTA units, which the authors took to mean that a carotenoid difference of at least about 50% is needed to change the ASTA value.
Caveat: One study, two origins; the threshold is the authors' inference from their samples.
StandardModerate evidence
ISO 3632 classifies saffron into three categories using the absorbance of a water extract at 440 nm for colouring strength together with two ultraviolet readings for picrocrocin and safranal and a limit on moisture.
Caveat: As described by an open research paper for ISO 3632-1:2011 and ISO 3632-2:2010. Colourwise has not read the standards, and the 2025 edition of Part 1 may have changed the categories or limits.
Source: Determination of Saffron Quality through a Multi-Analytical Approach; ISO 3632-2:2010 Spices — Saffron (Crocus sativus L.) — Part 2: Test methods; ISO 3632-1:2025 Spices — Saffron (Crocus sativus L.) — Part 1: Specification
FactStrong evidence
Saffron's colour comes from crocins, water-soluble glycosyl esters of the carotenoid crocetin, while paprika's comes from carotenoids including the orange-to-red xanthophylls capsanthin and capsorubin.
Source: Distribution of Main Bioactive Compounds from Saffron Species as a Function of Infusion Temperature and Time in an Oil/Water System; Chemistry, Occurrence, Properties, Applications, and Encapsulation of Carotenoids—A Review
FactModerate evidence
The ISO spectrophotometric test for saffron cannot reveal some adulteration with other plant material and cannot distinguish synthetic colourants from natural ones.
Caveat: Reported by researchers reviewing the method's limits; other parts of the standard cover identification tests.
Source: Determination of Saffron Quality through a Multi-Analytical Approach
Colourwise interpretationModerate evidence
An extractable-colour figure describes how much pigment a spice gives up per gram, so it is a guide to colouring power and not to the hue of the powder or of the finished dish.
Based on: Colourwise's reading of what a single-wavelength absorbance of an extract can and cannot represent, supported by the cited finding that ASTA units did not follow a 30% difference in carotenoid content.
Reviewed 1 October 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.