Those red hot chili peppers (no, not the band)

Are you a fan of spicy food, or do you steer clear of anything with spicy zest to it? I used to be reluctant to order anything remotely spicy in Thai restaurants, I would not cook with any peppers other than bell peppers, and merely the thought of deliberately adding cayenne pepper to my chili made my eyes water! However, over the last several years, my tolerance for spicy food has increased significantly. In that time, I’ve grown more familiar with a variety of peppers, many of which are now used regularly in my cooking. Ranging from jalapenos to habaneros, pepperocinis to scotch bonnets, and chilis to cayennes, peppers are arguably the biggest source of spiciness in the food that we eat.

So here’s a question for you - do you know why peppers are spicy?

The main culprit in the spiciness of peppers is a compound called capsaicin (pronounced kap-say-sin). Actually, capsaicin is a type of capsaicinoid. There are several capsaicinoids in pepper plants (which, incidentally, belong to the genus Capsicum). Capsaicin is the most abundant (accounting for about 70% of the total capsaicinoids), followed by dihydrocapsaicin (which makes up around 20%). There are also three minor related compounds (with fairly complex names), which total approximately 10% of the capsaicinoid load. Both capsaicin and dihydrocapsaicin are about twice as potent as the 3 minor compounds in terms of irritation. They are particularly strong against mucous membranes, including your mouth, nose and eyes. That means that, when you eat a pepper and your mouth burns, your eyes water, and your nose runs – you have mostly capsaicin to thank.

Capsaicin is produced by pepper plants at glands located at the junction of the placenta and the pod wall. (That’s the white “ribs” that run down the inside of a pepper.) As the peppers develop, it gets dispersed unevenly throughout the pepper, becoming heavily concentrated in the seeds. The seeds themselves do not produce capsaicin, but they are a major storage point for it. (So if you ever want to eat a pepper but don’t want all the spice, simply remove the seeds and the white ribs. That won’t get rid of all the spice, but it will eliminate most of it.) Capsaicin itself is not used as a metabolite for the plants, but it is theorized to be useful as a defense mechanism. Mammals generally will not eat peppers, presumably because they don’t like it when their mouths hurt! The peppers are eaten mostly by birds. For birds, capsaicin is an analgesic rather than an irritant - in other words, it acts as a pain killer, not a pain producer. It does them no harm, allowing them to pass the seeds through and deposit them for plant dispersal.

Capsaicin is an interesting molecule. For one thing, it is incredibly stable. It is unaffected by either cold or heat, and retains its spicy potency despite cooking or freezing. That means that you cannot cook the spiciness out of peppers. Another interesting fact is that capsaicin is not very soluble in water, but it is soluble in oils, fats and alcohols. Have you ever eaten something really spicy, then tried to quench the burning by drinking water? I bet it didn’t work. That’s because capsaicin does not dissolve well in water, so drinking water will not wash it off your tongue. You’d be better off drinking a glass of milk, which contains casein, a fat-loving compound that dissolves capsaicin much like soap dissolves grease.

Pure capsaicin is an incredibly powerful compound. At a cellular level, an exposure to capsaicin triggers calcium ions to flood into the affected cell, ultimately triggering a pain signal to the next cell. This is very similar to what happens during a thermal burn. A single milligram (which weighs 1/1000th as much as a paperclip) would be enough to blister the skin on your hand. When pure, it can only be handled by chemists wearing full body protection, including a closed hood to prevent the inhalation of the powder. Lloyd Matheson, a pharmaceutical chemist from the University of Iowa was reported to have once inhaled pure capsaicin accidentally; according to him, “It’s not toxic, but you wish you were dead if you inhale it.” Capsaicin also features prominently in pepper spray, which is a strong irritant for all of the mucous membranes on your face (eyes, nose, mouth, and respiratory system.)

But don’t worry. There isn’t enough capsaicin in peppers to be dangerous – only spicy! The spiciness of peppers is measured in terms of Scoville Heat Units, which is parts per million of capsaicinoid content. At the extremes of the scale are pure capsaicin and bell peppers. Pure capsaicin has a Scoville Heat Unit score of 16 million, while bell peppers have a score of 0. Here are the scores of other common peppers:
Habaneros: 100,000 – 300,000
Scotch Bonnets: 100,000 – 250,000
Thai Peppers: 50,000 – 100,000
Cayenne Peppers: 10,000 – 30,000
Jalapenos: 2,500 – 5,000
Pepperocinis: 100 – 500

As I said, I’ve gradually been increasing my tolerance for spiciness. Of course, I’m not munching on habanero peppers for an afternoon snack, but I can handle jalapenos, cayenne peppers, and even very small levels of Thai peppers. Of course, now that I know how potent Scotch Bonnet peppers are, I may have just reached my limit on the peppers I’m willing to try!