Wilbur Scoville invented the way we measure hot peppers' spiciness

How and why we measure the spiciness of hot peppers

Wilbur Scoville, honored as today’s Google Doodle to commemorate his 151st birthday, would probably be very surprised to learn that in 2016 he is primarily remembered for his research into spicy peppers — the namesake of the Scoville heat units.

Born in Bridgeport, Connecticut, in 1865, Scoville was a pharmacist, not a chef. And in his lifetime he was best known for his textbook The Art of Compounding, which was used as a reference material until well into the 1960s. But in addition to his academic research, he did practical work in the laboratories of the pharmaceutical company Parke-Davis, which in its day was America's largest drugmaker.

It was as a Parke-Davis employee — standing at the intersection of academic pharmacology and the practical needs of industry — that he developed both the "organoleptic test" of pepper heat and the Scoville scale to measure it, for which he is widely known today.

The invention of the Scoville scale

As John McQuaid recounts in his book Tasty, Scoville invented his scale as part of an effort to improve the production of Heet liniment, Parke-Davis's painkilling cream. The active ingredient in Heet was capsaicin, the key chemical that makes chili peppers spicy. To produce the cream, Parke-Davis needed to extract capsaicin from peppers. And to ensure the cream had a proper dosage of capsaicin, the company wanted to better measure how much was present in different peppers.
These days, you could directly measure capsaicin using high-performance liquid chromatography, but in 1912 the best they could do was use the human sense of taste.

The problem was that while it's easy to say that jalapeños are hotter than banana peppers but milder than habaneros, a pharmaceutical company needs to be able to quantify this precisely. Scoville's method was to dry out peppers and then dissolve a specific weight of dried pepper in oil in order to extract the flavorful compounds. The extract was then diluted in sugar water and given to a panel of five tasters. The amount of sugar needed to make the spiciness undetectable to a majority of tasters determines the Scoville rating of the pepper.

As it happens, this research turned out to be something of a pharmacological dead end. Heet is still on the market (though it shouldn't be confused with the antifreeze brand) and still contains capsaicin, but according to McQuaid, "the primary active ingredient is now methyl salicylate, derived from wintergreen," and "Parke-Davis never succeeded in making capsaicin into an effective, profitable product."

The world's hottest chili peppers

Capsaicin's promise as a pain reliever is intimately related to its culinary possibilities. The burning sensation capsaicin induces in the mouth leads the body to produce endorphins as a countermeasure. Eat spicy food regularly enough, and you start to associate the pain of pepper with the endorphins' pleasant rush. (That endorphin rush is the same reason some people start to love the pain of running long distances.)

A bit like addicts (though without the physical dependency), this leads some spicy food fans to chase ever-hotter flavors, and plant breeders have been eager to oblige them by devising hotter and hotter chilies.

While jalapeños generally clock in at 2,500 to 8,000 Scoville heat units and habaneros get up to 100,000 to 350,000 SHU, the Indian ghost chili packs a walloping 1 million SHU and was proclaimed the world's spiciest pepper by the Guinness Book of World Records in 2007. But in 2012, it was surpassed by the Trinidad moruga scorpion and then in 2013 by the Carolina Reaper, which continues to hold the title today. The Reaper, developed by Ed Currie's PuckerButt Pepper Company, rates a staggering 1.5 million SHU.