The Scoville scale is a measure of the hotness of a chile. These fruits
of the Capsicum genus contain capsaicin, a chemical compound which stimulates
heat-receptor nerve endings, and the number of Scoville heat units (SHU)
indicates the ratio of capsaicin present. Many hot sauces advertise
the Scoville rating of their sauce.
It is named after Wilbur Scoville, who developed the Scoville Organoleptic
Test in 1912. As originally devised, a solution of the pepper extract
is diluted in sugar water until the 'heat' is no longer detectable to
a panel of (usually five) tasters; the degree of dilution gives its
measure on the Scoville scale. Thus a sweet pepper, that contains no
capsaicin at all, has a Scoville rating of zero (no heat detectable
even undiluted); whereas the hottest chiles, such as habaneros, have
a rating of 300,000 or more, indicating that their extract has to be
diluted 300,000-fold before the capsaicin present is undetectable. The
greatest weakness of the Scoville Organoleptic Test is its imprecision,
because it relies on human subjectivity.
Later developments such as high pressure liquid chromatography (known
as "The Gillett Method") have now enabled the Scoville rating to be
determined by direct measurement of capsaicin rather than sensory methods.
*Scoville ratings may vary considerably within a
species—easily by a factor of 10 or more—depending on seed lineage,
climate and even soil. This is especially true of habaneros.
