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Chile Peppers: Hot Tips and Tasty Picks

What Makes Chile Peppers Hot?

by Paul Bosland

Contrary to conventional wisdom, chiles' seeds are not the source of their pungency. Rather, their "heat" is caused by capsaicinoids, alkaloids found only in chiles. Capsaicinoids are located in blisterlike sacs along the fruit's inner wall, or placenta. The sacs break easily when the fruit is cut open or handled roughly, and the capsaicinoids splash onto the seeds.

You can tell, just by looking, how hot a chile will be: Cut open the fruit and look at the walls. If the placenta is bright orange and there are many large sacs, the fruit will be very hot! If there is only a hint of color, the chile will be mild.

You can tell how hot a chile will be by cutting it open and looking at the walls. If the placenta is bright orange, the fruit will be very hot!

You can tell how hot a chile will be by cutting it open and looking at the walls. If the placenta is bright orange, the fruit will be very hot! (Photo: Paul Bosland)

The pungency level of any given chile is affected by its genetic makeup, the weather, growing conditions, and fruit age. Plant breeders can selectively develop cultivars within desired ranges of pungency, but any stress to the chile plant will elevate the amount of capsaicinoid in the pods. A few hot days can increase the capsaicinoid content significantly. Planting a sweet chile next to a pungent one will not cause the sweet chile to become pungent. But if you save seed from the fruits of the sweet chile for planting next year, the offspring will be pungent if the two plants exchanged pollen and hybridized. This is because pungency is genetically dominant, whereas sweetness is not.

There are 14 known capsaicinoids, among them capsaicin, the most common form. This chemical is so potent that the average person can detect its pungency at a dilution of 10 parts per million.

Chile pungency is expressed in Scoville Heat Units (SHU), named for Wilbur L. Scoville, who invented the scale in 1912. His Scoville Organoleptic Test was the first reliable measurement of the pungency of chiles. This test uses a panel of five human subjects who taste diluted chile extract. Water is added to a sample of extract until the pungency can no longer be detected; this dilution level is used to describe the chile's pungency. For example, a 5,000-SHU chile like jalapeño has had 1 part chile extract diluted with 5,000 parts water before the tasters can no longer detect pungency. A more potent chile—say, a 10,000-SHU serrano—would be diluted 10,000 to 1 for the same effect. While these chiles may be too pungent for many North American tastebuds, they're at the mild end of the Scoville scale: Habaneros can score up to 500,000 SHU.

Dousing the Flames

You just accepted that dare and ate a whole habanero. Your mouth is on fire, your heart is pounding, sweat is running down your face, and you're beginning to feel faint. How to extinguish the fire? This is a topic of great debate among chile aficionados. Some claim that plain water is best, while sugar, beer, bread, citrus fruits, tomato juice, and oil all have their advocates.

The latest scientific research, though, says that you should grab a jug of milk and have at it. Milk and milk-based products contain casein, a protein that unbinds the capsaicin—the source of the fire—from nerve receptors on the taste buds. Beans, nuts, and milk chocolate also contain casein, so they may also be effective coolants.

The organoleptic test has limitations. Tasters must be trained and can taste only a limited number of samples before they reach "taster fatigue," when their ability to detect pungency fails. Once widely used, the organoleptic test is being replaced by high-performance liquid chromatography (HPLC). This rapid test quickly processes a large number of chile samples and provides an accurate and efficient analysis of the capsaicinoids present. The instrument "sees" the capsaicinoid molecules and counts them, reporting pungency in parts per million. Pungency is still often expressed in Scoville Heat Units, though, arrived at by multiplying capsaicinoid parts per million by 15.

Like the instrument that performs HPLC, humans can perceive each of the 14 capsaicinoids differently. Different combinations of these capsaicinoids produce the pungency characteristics of individual chile varieties. So, while a habanero may have a sky-high SHU level, its bite isn't necessarily as irritating and persistent as a chile with a lower SHU rating like a Thai pepper.

The least irritating capsaicinoid is nordihydrocapsaicin, according to researchers at the University of Georgia. They found that the burning is located in the front of the mouth and palate, causing a "mellow warming effect." The pungency sensation develops immediately after swallowing and recedes rapidly. In comparison, capsaicin and dihydrocapsaicin were found to be more irritating, and were described as having a "typical" pungency sensation. Both compounds produce pungency in the middle of the mouth, the middle of the palate, the throat, and the back of the tongue. In contrast, homodihydrocapsaicin is very irritating, harsh, and very sharp. The pungency does not develop immediately but it affects the throat, back of the tongue, and the palate for a prolonged period.

Paul Bosland is a professor of horticulture at New Mexico State University. He is one of the foremost chile pepper breeders in the world, and is coauthor of The Pepper Garden (Ten Speed Press, 1995) and Peppers of the World: An Identification Guide (Ten Speed Press, 1996). he also contributed to BBG's 21st Century Gardening Series handbook Chile Peppers.