Review – The Science of Chilli Peppers

Pepper spraying an entire apartment full of dinner guests is a dramatic way to demonstrate the powerful effect of capsaicin on the tear glands and respiratory tract. Capsaicin is of course the mischievous chemical responsible for watery eyes, hiccups, and the fabled “exit burn” that the planet has come to associate with a poorly judged dose of hot chillis. In my case, I left an oily pan on the stovetop for too long before adding several fistfuls of finely chopped bird’s eye chillis to its red hot centre. The resulting plume quickly spread throughout every room of the tiny flat and a crying, choking group of about 10 people spent 15 minutes huddled outside, staring at the open windows as the appetisers and mood went cold. Despite my best attempt to improve the atmosphere with an invigorating and impromptu lecture on the chemistry and biology of this testy molecule, the evening remained mired in infamy. I mean, it’s pretty bad when a chemistry story doesn’t cheer people up.

Chillis have really come into the mainstream, with aficionados and breeders alike creating an absolutely volcanic market and a surge of new products that flows as relentlessly as lava. These aren’t your granddad’s pickled jalapeños, either. Chilli cultivars are getting hotter and hotter thanks to the twisted horticulturists that take pleasure in turning a vegetable flamethrower on the human mouth. The Carolina Reaper literally looks like Satan giving you the finger, but newer and hotter varieties are on the way that will make even that seem like a warm and snuggly mouth hug in comparison.  It hasn’t always been like this. In fact, the origin of the hot pepper may surprise you.

Researchers have combed through genetic data, linguistic references, and combined archaeological and ecological evidence to broadly identify a region of south-east Mexico as the birthplace of the domesticated chilli, some 6500 years ago, at least. These were Capsicum annuum, the most abundant of the five chilli species and the one to which belong jalapeños,bell, and cayenne peppers. This certainly explains why Texan barbecues are heavy on chipotles (smoked jalapeños), but why do Naga Jolokias come from India? Shortly after the European discovery of the Americas, old world chefs began to chatter about exotic new vegetables and spices exported back across the ocean. One of these, known as “chilli” in the native tongue, was pungent and reminiscent of the piquant Indian spice, pepper. The fire locked within them set them apart, however, and they quickly gained the label “hot peppers”. Portuguese merchants eager to exploit new trading possibilities loaded them aboard their vessels on their eastward trips to the Orient, winning over entire kingdoms with the startlingly bold and strikingly coloured fruit. Nowadays it is impossible for us to separate chillis from the cultures that have so painstakingly written them into their national cookbooks. Can you imagine India without vindaloo curries or Thailand without tom yum?

Capsaicin itself is a chemical defence against unsuspecting mammalian predators, and there is some evidence it may prevent attacks by invasive fungi as well. Birds are not sensitive to the pungent compound, and actually help to spread the plant and secure its future as they drop undigested seeds across their environment. Novice tasters are often warned not to eat the seeds of a chilli, but this is not the most potent domain of the fruit. All of the capsaicin is produced in the white ribs, or placenta, of the pepper, gradually infiltrating the seeds and inner walls over time. Capsaicin production is heightened in a hot, dry climate and is dictated by the genetics of the specific breed. The Scoville Scale ranks the capsaicin wow factor of the world’s best known chillis and is a great guide for enthusiasts looking to score bragging points by choking back Trinidad Scorpions or habaneros. An ancho pepper weighs in at  a paltry 2000 Scoville Heat Units (SHUs), while a habanero tops out at 350 000. The current record holder, the Carolina Reaper, has been tested at up to 2 200 000 SHUs. That is one THOUSAND times hotter than an ancho. Crikey.

The way capsaicin interacts with your body to create that unbridled river of fire through your digestive tract is extremely well understood. A protein receptor called TRPV1 processes the signals that are eventually recognised by your brain as “OMG – WTF!!” and sends you running for a glass of water. Thankfully, after 10 minutes or so the receptor has exhausted itself and the pain signal fades away. This is the basis for the use of capsaicin creams as antinociceptives, agents that diminish painful sensations. After initial application to a painful area, the sensation will subside and a gradual numbing will set in. Of course the drawback is that you have to endure 10 minutes of intense burning before this happens. Newer medicines attempt to block this signal altogether, though in practice they invariably flick another of TRPV1’s switches – the one that controls body temperature – causing it to rise uncomfortably.

One final piece of trivia solves the “traffic light pepper” mystery. Why do green bell peppers have such a raw, herbal taste while red bell peppers burst with sweet floral flavours? Almost all chillis turn from green to either yellow, red, or purple when ripe. Green is just an indicator that they still have a way to go. In the case of bell peppers the yellow is the midway point between green and red.

Now go out and put all this theory into practice. Start with some Devilish Lemongrass and Chilli Sauce and then get to work on your own recipes.

More questions on the science of chillis? Ask away!


Science of Chilli Peppers - Immortal Pestle


  1. May 31

    Wow! Wonderful blog and simply gorgeous photography. In particular the movement of the chilis for this post is stunning. Well done!

    Suggestion: I posted your image to Pinterest, and I’m not sure if you know this, but you might want to give your image a better name in the “alt tag/description” to match or closely match your post title. Makes for better SEO, AND when I pin I can’t change the name so someone looking at my pins won’t know what the images is referring to.

    I look forward to seeing your site grow!


  2. Immortal Pestle
    May 31

    Thanks, Darren!

    A great tip and duly noted – I will get on my photos to make them more SEO friendly. Happy you visited and enjoyed the site!


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