A good question, and one that most people don’t really know the answer to.
Now bare with me guys as we delve into a little bit of science. Not too much I promise.
What makes chillis hot is the amount of capsaicin (cap-say-sin) they contain, that is the chemical responsible for the burn. Quite simply, the more capsaicin the hotter the chilli. But interestingly not all parts of the chilli have the same heat. It’s not the outer skin that is the hottest, nor the seeds, however, they are hotter than the skin. It is the white fleshy part inside the chilli that houses the seeds that is the hottest; and this is called the placenta.
People have been testing the heat of chillis for over 100 years now. The first to formalise it was a pharmacologist named Wilbur Scoville way back in 1912. He devised a test which involved soaking dried chillis in pure alcohol to extract the capsaicin. He progressively diluted the infused alcohol in a solution of sugary water to get a range of sample concentrations. He then gave these samples to five human guinea pigs who each assigned the sample a heat rating, which he called a SHU (Scoville Heat Unit); thus the Scoville Scale was created.
Well as you can imagine it wasn’t the most precise means of testing as it was subjective and could vary depending on the taster’s palate and how they tolerated heat; and probably how much alcohol they consumed.
Surprisingly this form of testing continued until around the 1980s when chilli science got serious. Then a more quantative test called high-performance liquid chromatography (HPLC) was introduced which removed the need for human guineapigs. It may be more reliable, but nowhere near as much fun.
All chillis have a SHU so you can get some idea of how hot a chilli is before you pop it in your mouth, if you want to know. Today chillis range in heat from 0 (your ordinary capsicum) to 1.5 - 2million for the Carolina Reaper which is the hottest chilli in the world at the moment; and there are a couple of new ones undergoing testing now. A guy called Ed Currie who created the Carolina Reaper has been a cultivating a new chilli for the last 10 years called Pepper X which has an unofficial SHU of 3.1M. That is serious heat my friends and to put it in context, police capsicum spray is anywhere from 2 - 4.5 million.
Here at Hot Chilli Mama central we grow a range of chillis from 1250 SHU (Poblano - below) to 1.5 - 2million (Carolina Reaper - right) and I can assure you that you do not muck around with these bad boys. You should always wear gloves when touching them and safety glasses when cooking with them. And remember don’t touch your eyes or other sensitive areas (you know what I mean) after touching chillis. Hot Chilli Daughter recently got Carolina Reaper in her eyes in a slight bottling mishap and I’m surprised you all didn’t hear her, poor kid. She won’t be helping with that sauce again anytime soon. Safety glasses when cooking for us from now on.
Now for an interest fact, did you know that whilst you and I feel the heat, not all critters do. Birds for one. I found that out the hard way having lost thousands of chillis to a marauding flock of crimson rosellas. I was watching them from afar, marvelling at the majestic sight until I realise they were feasting in my chilli patch. Free loaders, and they don’t eat all of the chilli, no they just take the top out of them and then dump them onto the ground and go for the next one. Answers - birds nets and a chilli dog that loves chasing them if they come near.
So the next time you want to know how hot a chilli is, check out its Scoville rating.