“All chilies belong to the genus Capsicum,” Nicks says. “Chili peppers have unique tastes and aromas across a wide spectrum, owing to varying combinations of hundreds of different chemical compounds. It is the odorless, tasteless, crystalline chemical compound known as capsaicin that stimulates nerve endings in the mouth and skin, triggering production of the neurotransmitter called substance P. This in turn signals the brain that the body is in pain, specifically because it is on fire.”
He explains how capsaicin is nearly insoluble in water, which is why drinking a glass of water after consuming chili peppers does not reduce the pain. On the other hand, capsaicin is soluble in fat and alcohol, which is why a cold beer and some blue cheese dressing often accompanies a plate of hot wings.
A wide range of peppers
The pungency of a chili pepper – its concentration of capsaicin – is measured in Scoville Heat Units (SHUs). This was originally determined using a test that measured the degree to which a chili pepper solution must be diluted before capsaicin was no longer detectable to a professional taster.
“Nowadays a less subjective test – high-performance liquid chromatography – is used to analyze capsaicin content, but heat is still generally described in SHU,” Nicks says. “Pure capsaicin tops out the Scoville scale at 16,000,000 SHU.”
To compare, bell peppers, which are part of the Capsicum genus, lack capsaicin. They score zero on the Scoville scale.
“As any astute chili eater knows from experience, the mere ‘spiciness’ of a chili does not tell the whole story,” Nicks says. “Some chilies come on fast, while some come on slow. Some strike and vanish, while others linger.”
In fact, capsaicin is just one of more than 20 compounds known as capsaicinoids. It is the unique combinations of capsaicinoids in the many chili peppers that give each pepper a different degree of perceived heat.
Chili peppers also have flavor, which sometimes can get lost in the heat. For example, ancho peppers, also known as poblanos, are 1,000 to 2,000 SHU. They possess a rich, dark cherry and raisin sweetness. Chipotles range from 2,500 to 10,000 SHU, and are made by smoking and drying jalapenos; thereby, having a woodsy, smoky flavor.
Guajillos are dried mirasol chilies, which are only about 2,500 to 5,000 SHU. They boast a moderately spicy, tangy flavor with a touch of citrus. Pasillas are even milder, at 1,000 to 2,500 SHU. Their unique, complex flavor starts out like prune and finishes with a hint of licorice.
There are a number of varieties of habanero peppers, ranging from little to no heat to fiery hot (500,000-plus SHU), which makes them so popular, as they can be blended together or with other ingredients to develop unique flavor profiles. In general, habaneros possess a fruity, citrusy flavor, which is why they are often paired with fruits, with mango being the most common.
At 800,000 to 1,000,000-plus SHU, the Bhut Jolokia pepper, also known as ghost pepper, was certified as the hottest chili pepper on the planet in The Guinness Book of World Records in 2007, but no longer holds that title. As of August 2013, the Carolina Reaper, which can be as hot as 2,200,000 SHU holds the title. There are also more than 10 other peppers that have since been identified that are hotter than the ghost pepper. As you can imagine, with such hot peppers, the human palate can only experience the heat. These peppers contribute no flavor to food applications.