I always found it interesting that our way of rating spiciness is through the subjective Scoville scale. Directly from wikipedia:
> In Scoville's method, an exact weight of dried pepper is dissolved in alcohol to extract the heat components (capsinoids), then diluted in a solution of sugar water.[3][4][5] Decreasing concentrations of the extracted capsinoids are given to a panel of five trained tasters, until a majority (at least three) can no longer detect the heat in a dilution.[4][5][6] The heat level is based on this dilution, rated in multiples of 100 SHU.[4]
In other words, the test is fully subjective and has been found to be unreliable:
> A weakness of the Scoville Organoleptic Test is its imprecision due to human subjectivity, depending on the taster's palate and their number of mouth heat receptors, which varies greatly among people.[6] Another weakness is sensory fatigue:[6] the palate is quickly desensitised to capsaicins after tasting a few samples within a short time period.[4] Results vary widely (up to ± 50%) between laboratories
Radiation exposure is measured in becquerels, grays, and sieverts, for the decay rate, absolute absorbed quantity of radiation, and relative effect on human tissues.
Piquancy exposure is measured only in scoville-heat-units, which is the spiciness equivalent of the sievert. Clearly, piquancy is in need of at least one additional unit that can abstract away the variations in mammalian tongues. That number, in combination with your personal taste profile, would allow you to predict the perceived spiciness of any given dish when you eat it.
You would just need to objectively measure the concentrations of capsaicinoids, and their TRPV1-activating analogs, put those into a spreadsheet with your own numbers, and determine how piquant something would be in scoville-heat-units when you, specifically, eat it.
It's not "fully subjective" by any sensible definition. Yes humans are the measurement device, and humans differ and are unreliable, but given a sufficient number of samples you arrive at more accurate numbers.
Nobody's going to give a paprika the same rating as a Carolina Reaper. You might have some give two very strong peppers the same rating, but then you might just need more people to test it.
In any case, the practical utility of the scale is mostly to get an idea of how spicy something is, it doesn't really matter much if something is 700K or 600K, it's enough to know that it's around 2x as strong as a Habanero.
No, the Scoville test is based on a comparison of diluted samples. Trials are rerun with increasing dilution until the testers cannot detect the sample, and the level of dilution determines the score.
> In Scoville's method, an exact weight of dried pepper is dissolved in alcohol to extract the heat components (capsinoids), then diluted in a solution of sugar water.[3][4][5] Decreasing concentrations of the extracted capsinoids are given to a panel of five trained tasters, until a majority (at least three) can no longer detect the heat in a dilution.[4][5][6] The heat level is based on this dilution, rated in multiples of 100 SHU.[4]
https://en.wikipedia.org/wiki/Scoville_scale#Scoville_organo...
In other words, the test is fully subjective and has been found to be unreliable:
> A weakness of the Scoville Organoleptic Test is its imprecision due to human subjectivity, depending on the taster's palate and their number of mouth heat receptors, which varies greatly among people.[6] Another weakness is sensory fatigue:[6] the palate is quickly desensitised to capsaicins after tasting a few samples within a short time period.[4] Results vary widely (up to ± 50%) between laboratories