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How Hot Is Hot?
August 24, 2000
Whoa, hot!

When it comes to peppers, some like it hot, and some like it hotter. But how can we tell before taking the first bite?

At one time, human tasters were used to determine how hot chile peppers were. But today, there is a scientific technique that can do the same thing—without burning anyone’s taste buds.

Method to the madness

The method, called high performance liquid chromatography, or HPLC, works by counting the number of capsaicin molecules in chile peppers. Capsaicin (cap-SAY-isin), the stuff that makes peppers hot, is related to a family of chemicals which include vanillin, common in vanilla extract. "In fact," says David Henderson, professor of chemistry at Trinity College, "if you look at the capsaicin molecule, one end is basically a vanilla molecule and the other end is like a big piece of diesel fuel, and they’re linked together and make capsaicin."

In order to determine hotness, experts dry and ground chiles and make a solvent which they inject into an instrument—the HPLC device—to separate the capsaicin from other molecules. Then they measure how much of it is present in terms of scoville units. This method has been used since the 1980s.

Scoville units, however, were first devised in 1912 by Wibur Scoville, a scientist bent on coming up with a method to measure the hotness of chile peppers. In his method, capsaicin was extracted with alcohol and the solution was diluted with sugar water. The dilutions were made in factors of 10, then given to a panel of human tasters. They started tasting with the least concentrated solution and worked their way up. When the testers first encountered the trademark bite of chile peppers, the first scoville unit was assigned.

Even though human testers aren’t used to measure the heat in peppers anymore, scoville units are still used with the high-tech HPLC method. In terms of scoville units, bell peppers rate zero, while jalapenos rate between 3,500 and 4,500. Tabasco peppers rate between 30,000 and 50,000 scoville units, but the hottest pepper, the red savina habanero, is assigned a value of up to 300,000. [See chart of pepper hotness.] Pure capsaicin would have a value of some 16 million units. That means that to dilute it down so that you could just barely taste it would involve adding about 4,000 gallons of sugar water to one gram of capsaicin.

What makes your mouth burn

image: McIlenny Co.

Capsaicin, found mostly in the seeds and ribs of peppers, acts on the same receptors on the tongue that measure temperature. When you put it in your mouth, it stimulates the nerves that give you a sensation of heat, and they release a neurotransmitter called substance P into your blood, sending signals to your brain telling it you’re eating something hot, explains Henderson. "So capsaicin really does mimic heat in the mouth and on the skin as well," he says.

"The other thing that capsaicin does—and this may be the reason people like to eat chiles so much—is that when substance P is released into the bloodstream, the body produces chemicals called endorphins, and endorphins bind to the same receptor in the brain that morphine does, so they make you feel good," says Henderson. But they don’t bind for very long and they’re not addictive, he adds.

The idea of getting used to spicy foods also has an explanation, because it’s possible to build up a tolerance to capsaicin. "If you brush your tongue with a solution of one part per million capsaicin and wait 20 minutes and you then brush your tongue with 10 parts per million capsaicin, it will have just about the same sensation that the one part per million did earlier," says Henderson.

Hot benefits

Chili peppers are fruits of the plants in the genus Capsicum whose medicinal value is widely recognized. Their use dates back to the 1500s, when they were used to treat ailments as varied as skin and eye infections, heart conditions, and colds. Today, capsaicin is used in anti-inflammatory creams to treat arthritis, shingles and neuralgia. In 1994, researchers at the Yale University School of medicine used chile peppers in a candy that reduced mouth pain in cancer patients. The sugar in the candy helped cut down on the burn caused by capsaicin.

Cayenne, or hot pepper, is also used in alternative medicine. It works as a circulatory and digestive stimulant, and can be helpful in treating psoriasis, since it relieves pain and itching. It’s also said to be very effective in treating delirium tremens, reducing the craving for alcohol and promoting digestion.

There is no evidence that eating too many spicy peppers is bad for you, or that it causes ulcers. "I think if you eat enormous amounts of capsaicin all the time you might eventually damage some of the nerves in the tongue, but occasional use certainly isn’t going to cause a problem," says Henderson.

If you do burn your mouth with peppers that are too spicy, it won’t do any good to drink water, because capsaicin is not soluble in water. What you really need is fat, according to Henderson, who recommends drinking milk or eating yogurt or ice cream. "What I do is I coat my tongue with peanut butter," he says, "because I like peanut butter anyway."

In print:

The Chile Pepper Encyclopedia: Everything You’ll Ever Need to Know About Hot Peppers, With More Than 100 Recipes, by Dave Dewitt

Elsewhere on the web:

The Chile Pepper Institute

The botany of chile peppers

The history of peppers

American Botanical Council

Henriette’s herbal homepage

by Jill Max

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