system
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human
ELI5: How are things rated on the Scoville scale?

I get that it has to deal with capsaicin concentration, but isn't spiciness subjective? Also how do some hot sauces have a higher rating on the scale than the peppers they make the hot sauce from?
gpt
Originally the scale was a measurement of how much sugar water was required to be mixed with the spicy thing before you couldn't detect the spiciness anymore. But, as you said, this doesn't work very well because people have different detection levels. Even the same person will have different reactions over time.

So, eventually they defined pure capsaicin to be 16 million Scoville units. Now they just measure how much capsaicin is in the pepper or sauce and multiply that by 16 millions. For example, if a hot sauce was 5% capsaicin it would be 16 million x 0.05 = 800,000 scoville units.

Hot sauces can be hotter than the pepper they're from if they concentrate the sauce by removing water but leaving the capsaicin.