Capsaicin is a chemical compound and the main culprit for giving a chilli its heat. It exists mainly in the placenta, the white tissue running down through the chilli which holds the seeds. Some may say the seeds are the hottest part of the chilli, when in fact they are not. Seeds do not produce any capsaicin, but because they are attached to the inner wall of the placenta where the highest concentration of capsaicin exists, seeds tend to exhibit some heat.
The Scoville heat unit is a way of measuring the concentration of capsaicinoids, where capsaicin is the main component. The measurement is based on a dry unit mass of the chilli, so concentrations can vary greatly depending on the amount of water in the chilli and the variety. SHU is essentially a measure of how much dilution is needed based on multiples of 100 SHU till you can no longer taste any heat.
Although several chillies have been formally tested worldwide to be assigned an officially SHU (such as the Carolina Reaper to name one), there are many factors which contribute to the heat level which may differ to the SHU obtained in a laboratory.
Growing conditions which includes the amount of sun the plant receives, how often it’s watered, the type of strain, fertilisers, soil mix, and so on can all be contributing factors which affect the SHU. So although a chilli may formally test to 1,500,000 SHU in a lab, that does not mean all chillies from that particular strain or plant will be 1,500,000, because it’s based on varying growing conditions, and the amount of water an individual chilli may take up while on the plant. Some Carolina Reapers may be lower or higher then 1,500,000 SHU, and the same applies to all varieties sold.
Then there are chillies varieties worldwide which have never been formally tested, so they may be given a SHU guesstimate based on people’s experience throughout the years.
This is why we give a range of SHU on all our chillies.
Everyone’s palate is different, and what someone finds hot, may not be as hot to someone else. Some people are just born with a higher tolerance for spicy food then others as well, especially if they’ve been brought up as a infant in a culture of spicy food. There are also people who have built a tolerance for spicy food over time. Someone who has developed a tolerance for superhot chillies over the years, may find a Habanero to be a tingle, compared to someone who has little tolerance to chilli, who finds a Habanero to be extreme.
A general guide to varieties as you move up the SHU scale can be found below. If you’re wanting to explore the world of spicy food, start small and work your way up. It’s like going to the gym and consistently working on the same muscle group. That muscle will eventually get bigger, and be able to lift more weight.
Don’t let a heat level score of 10+/10 for a Carolina Reaper confuse you. It’s currently the world’s hottest chilli, and whilst some score it 14/10, we like to keep things as simple as possible using a scale of 1-10+, with 10+ being the hottest chilli currently available. We base our score on the estimated (or known/recorded by others) SHU mixed in with some experience in tasting. Going beyond this number doesn’t really make sense. You can’t score 140% on an exam for example, but you can score an A+.