I understand that the heat of peppers is measured in Scoville Units.  What is a Scoville?

--Richard

You are right that the heat or pungency of peppers is measured in Scoville Units.  The term is named after an American chemist by the name of Wilbur Scoville.  To compare the heat of peppers, he mixed samples of various peppers with a sugar water solution and then had a panel of tasters taste each mixture.  The lowest dilution at which the panel could no longer detect the heat from the sample was taken as the measure.  For example, if a given pepper had to be diluted 50,000 to 1 before the panel agreed that the heat was no longer noticeable, then that pepper was said to rate at 50,000 Scoville Units.

By collecting numerous data points for each kind of pepper, a scale could be derived.  According to that scale, common Sweet Bell peppers rate between zero, no heat, and about 500 Scovilles.  Jalapenos rate between 2,500 and around 10,000 Scovilles, and so on.  The hottest pepper that is commonly available is the Habanero or Scotch Bonnet which comes in around 100,000 to 250,000 Scovilles.

The test, as done by Scoville, has a number of shortcomings, not the least of which is the subjectiveness of a tasting panel.  Results can vary widely from panel to panel.  Also, individual specimens of any given type pepper can range quite dramatically in strength, depending on age, growing conditions and other factors.

Scoville's original work was done in 1912.  Nowadays, this method is replaced with more accurate methods of extracting just the capsaicin from a sample and measuring quite accurately the amount present.  Capsaicin is the chemical that gives peppers their heat.  Pure capsaicin rates around 16 million Scoville Units.