The Scoville Scale Explained
American pharmacist Wilbur Scoville originally developed the Scoville Organoleptic Test in 1912. It was created as a way to quantify the burn (spiciness, heat) of various peppers.
First, an alcohol extract of capsaicin oil is obtained from the dried test pepper. This oil is then diluted with sugar water at differing concentrations and sampled by “taste testers”. The pepper is then assigned a Scoville Heat Unit with respect to the dilution required for the “burn” to no longer be sensed. For example, if a pepper rates at 5,000 Scoville Heat Units, then the oil obtained from the extract must be diluted 5,000 times before the heat is barely detectable. The most common peppers have been charted on what is commonly know as the Scoville Scale with respect to their Scoville Heat Units.
In essence, this test measured the relative amounts of capsaicin in each pepper. Capsaicin is the natural chemical that makes your tongue burn, body sweat and ears ache after eating a pepper. For more information on the reasons for the burn, see Behind The Burn.
Since a taste test panel is inherently subjective, today High Performance Liquid Chromatography (HPLC) is used as a more scientific and accurate way of measuring capsaicin concentration. The American Spice Trade Association (ASTA) uses HPLC to accurately measure capsaicin (and other “burn” producing chemicals) in foods and assigns a unit of measure called the ASTA Pungency Unit. 1 ASTA Pungency Unit equals approximately 15 SHUs. Most sources report that even with this conversion the results are about 20-40% lower than the results from the Scoville method. Even though a ASTA Pungency Unit is a more accurate measure of heat the Scoville Scale in much more widely known and used.