Peppers and Chillies

TL;DR. Chilli heat is not a taste. Capsaicin binds to TRPV1, the receptor that detects heat above about 43 °C, so your brain receives a genuine burning signal from a stimulus that is not hot. Birds are immune to it, which is exactly the point: the plant wants birds to disperse its seeds and mammals to leave them alone. Sweet peppers are the same species with a broken capsaicin gene, and red peppers contain roughly three times the vitamin C of an orange, making them one of the best sources in the shop. Water does not help the burn; fat and dairy do.

1. What they are

Genus Capsicum, family Solanaceae. Botanically a berry.

Sweet peppers are chillies with a mutation that disables capsaicin synthesis. They are the same species as jalapeño and cayenne.

2. Where they come from

Central and South America, domesticated at least 6,000 years ago in Mexico and separately in the Andes and Amazon. Columbus encountered them in the Caribbean and, seeking black pepper, called them "pepper," which is why an unrelated New World fruit shares a name with an Asian vine (Piper nigrum, Chapter 49).

Their spread after 1492 is one of the fastest and most complete adoptions in food history. Within a century, chillies had become central to the cuisines of India, Thailand, Korea, Sichuan, Hungary, and West Africa. It is genuinely difficult to imagine those cuisines beforehand: Indian food had long pepper and black pepper, Korean food had no gochujang, Sichuan food had Sichuan pepper but no heat as we know it. Chillies were cheap, easy to grow, and provided intensity that expensive imported spices had monopolised.

Production: around 40 million tonnes of green peppers and chillies plus around 5 million tonnes dried. China, Mexico, Turkey, Indonesia, and Spain lead the fresh trade; India dominates dried chilli production and export.

3. How they are grown

Warm-season perennials grown as annuals in temperate climates. They want 20 to 30 °C and a long season. Below 15 °C growth stalls; above 32 °C flowers drop.

In tropical climates they are genuinely perennial and a chilli plant can crop for several years, which surprises northern gardeners.

Self-pollinating, though insects increase yield, and cross-pollination between varieties in a garden means saved seed is unpredictable, which is how people end up with unexpectedly hot "sweet" peppers.

Heat is not fixed by variety alone. Capsaicin content varies with:

• Genetics, which sets the range.
• Water stress: drought stress substantially increases capsaicin. Hot chillies get hotter in a dry year.
• Temperature and light: higher heat increases capsaicin.
• Ripeness: capsaicin generally rises as the fruit matures.
• Position on the plant and even fruit to fruit on the same plant.

So the Scoville rating of a variety is a range, sometimes spanning an order of magnitude.

Colour development. All peppers start green. Left on the plant they ripen to red, yellow, orange, purple, or brown depending on variety, becoming sweeter and substantially higher in vitamin C and carotenoids. Green peppers are unripe. They are picked green because they yield more per plant (the plant keeps setting fruit) and ship better, which is why they are cheaper.

Paprika and dried chilli production involves drying ripe fruit and grinding; smoked paprika (pimentón) is dried over oak. Capsaicin is not destroyed by drying, so dried chilli is more concentrated by weight.

4. What is inside them

Per 100 g raw:

The vitamin C numbers are the headline. A red bell pepper contains roughly three times the vitamin C of an orange per 100 g, and yellow peppers more still. Peppers are among the best vitamin C sources in an ordinary diet, and this is not widely known.

This is not a coincidence of history: Albert Szent-Györgyi won the 1937 Nobel Prize partly for isolating vitamin C, and he did it from Hungarian paprika, which he realised was an extraordinarily rich source available in kilogram quantities.

Ripening transforms them. Red peppers have around 60 percent more vitamin C and eight times the vitamin A of green ones. Choosing coloured over green is one of the easiest nutritional upgrades available.

Carotenoids: red peppers contain capsanthin and capsorubin (unique to Capsicum), plus beta-carotene; orange and yellow contain zeaxanthin, lutein, and violaxanthin. Paprika is one of the most carotenoid-dense foods by weight.

5. Capsaicin: how heat works

In short: Capsaicin binds the receptor that detects damaging heat, so your nervous system reports burning from a stimulus that is not hot.

TRPV1 is an ion channel on sensory neurons that opens in response to temperatures above about 43 °C, to acid, and to certain chemicals. Its job is to signal "this is hot enough to damage tissue."

Capsaicin binds TRPV1 directly and opens it. The neuron fires exactly as it would if you were being burned. The brain has no way to distinguish the two signals, so it produces pain, sweating, flushing, vasodilation, tears, and a runny nose: a full thermoregulatory response to a non-existent temperature. Nothing is actually being damaged.

The mirror image is menthol, which activates TRPM8, the cold receptor, which is why mint feels cold.

Why the plant does it. Capsaicin deters mammals, which chew and destroy seeds. Birds lack the capsaicin-sensitive form of TRPV1 and feel nothing, and they swallow fruit whole and disperse seeds intact over long distances. Chilli heat is a targeted message: birds yes, mammals no. Humans are the one mammal that decided to override it.

Scoville Heat Units originally measured how much sugar water was needed to dilute an extract until a taste panel could no longer detect heat. Modern measurement uses HPLC to quantify capsaicinoids and converts to SHU.

Where the heat is. Not in the seeds, which is the most persistent myth here. Capsaicin is produced in glands on the placenta, the white pithy membrane the seeds attach to. Seeds are hot only by contact. Removing the membrane removes most of the heat.

Desensitisation is real. Repeated exposure depletes substance P in the sensory neurons and downregulates the response, which is why tolerance builds with regular eating and why capsaicin creams are used therapeutically for neuropathic pain: sustained application exhausts the pain neurons.

What relieves the burn. Capsaicin is fat-soluble and not water-soluble.

6. What the evidence actually shows

Established: peppers are exceptional vitamin C sources, better than citrus. Capsaicin acts on TRPV1 and topical capsaicin is a licensed treatment for neuropathic pain, including post-herpetic neuralgia and diabetic neuropathy, where high-concentration patches have good trial evidence.

Strong: capsaicin produces a small, real increase in energy expenditure and fat oxidation, and a small reduction in appetite, in controlled studies. The magnitude is on the order of tens of calories a day and is not a weight loss strategy.

Mixed: large cohort studies in China (the China Kadoorie Biobank, nearly 500,000 people) and in the US and Italy have found associations between regular chilli consumption and lower all-cause mortality, in the region of 12 to 23 percent. The findings are consistent across populations, which is interesting, and observational with obvious confounding by dietary pattern and by who eats spicy food.

Thin: chilli for cancer prevention or treatment. Capsaicin supplements for weight loss at meaningful magnitude.

A genuine hazard worth naming: very hot chilli consumption has caused oesophageal perforation (from violent vomiting), thunderclap headache with reversible cerebral vasoconstriction (a documented case after a Carolina Reaper eating contest), and severe gastrointestinal distress. Chilli-eating contests are not a safe activity.

7. Who should eat more, who should be careful

Good for: most people. Coloured sweet peppers should be eaten far more than they are, purely for the vitamin C and carotenoids.

Be careful if:

• You have reflux (GORD), IBS, or an anal fissure/haemorrhoids. Capsaicin directly irritates and is a common trigger at both ends. TRPV1 receptors line the whole gut.
• You have a peptic ulcer. The old belief that chilli causes ulcers is wrong (ulcers are caused by H. pylori and NSAIDs), and capsaicin may even be mildly protective of the gastric mucosa, but it can irritate an existing one.
• You wear contact lenses or have children. Capsaicin transfers on hands and persists through ordinary washing. Handling hot chillies and then touching eyes, or a child's eyes, is genuinely painful. Wear gloves for very hot varieties, and wash with oil or soap rather than water alone.
• You have a nightshade sensitivity. As elsewhere, not supported generally.
• You are giving chilli to a child. Tolerance is learned and there is no harm in it; there is also no reason to hurry.

Ages. Sweet peppers from 6 months, cooked soft or as raw strips for older babies. Chilli heat is a cultural matter, introduced gradually in cuisines that use it, and there is no evidence of harm from age-appropriate exposure.

8. When and how to eat them

• Buy red, yellow, or orange rather than green. Ripe peppers have far more vitamin C and vitamin A, and they taste better. Green peppers are unripe.
• Eat some raw for the vitamin C, which is heat-sensitive.
• Roast or char them for flavour: blistering the skin under a grill or over a flame, then steaming in a covered bowl and peeling, transforms them completely and is the basis of countless Mediterranean dishes.
• Remove the white membrane, not the seeds, to control heat.
• Bloom dried chilli and paprika in fat, not water: the capsaicinoids and carotenoids are fat-soluble, so frying spices in oil for 30 seconds extracts far more flavour and colour than adding them to a watery pan.
• Do not burn paprika. It scorches and turns bitter almost instantly at high heat.
• Ferment them. Most hot sauces are fermented chilli mash; gochujang and doubanjiang are fermented chilli pastes and are among the most useful savoury ingredients there are.
• Keep dairy on the table if serving very hot food.

9. Choosing and storing

Choosing. Firm, glossy, heavy for size, with taut unwrinkled skin and a fresh green stem. Avoid soft spots and wrinkling. For chillies, firmness and glossiness matter more than size.

Storing. Peppers are chilling-sensitive but store best cold in practice.

• Fridge, in the crisper, unwashed, in a perforated bag: sweet peppers 1 to 2 weeks, chillies 2 to 3 weeks. They will pit and soften eventually below about 7 °C, which is why they do not last indefinitely.
• Do not store cut peppers uncovered, they dry out fast.
• Freeze them. Peppers and chillies freeze well without blanching, whole or sliced; the texture softens but flavour and heat hold. This is the best way to deal with a glut.
• Dry chillies by threading on string in a warm airy place, or in a low oven. Fully dried chillies keep for a year or more; store in the dark, because light degrades the carotenoids and fades the colour.
• Paprika and chilli powder degrade fast. Buy small quantities, store in the dark, and replace annually. Faded paprika has lost most of its flavour and carotenoids.

10. The varieties worth knowing

Sweet: bell (green, red, yellow, orange, purple), Romano/sweet pointed (sweeter and better flavoured than bells, worth seeking out), padrón and shishito (small green frying peppers, mostly mild, with roughly one in ten hot, which is the entire point), piquillo (Spanish, roasted and tinned).

Mild to medium: poblano (fresh) and ancho (the same dried, sweet and raisiny), Anaheim/Hatch, jalapeño (fresh) and chipotle (the same smoked and dried), guajillo, Kashmiri (mild, prized for deep red colour), Aleppo/pul biber (Turkish and Syrian, fruity), espelette (Basque, PDO).

Hot: cayenne, serrano, bird's eye, Scotch bonnet (essential to Caribbean cooking, fruity as well as hot), habanero, rocoto.

Extreme: ghost pepper, Trinidad Scorpion, Carolina Reaper. These exist for competition rather than cooking.

Paprika: Hungarian (from sweet to hot, graded by grind and pungency) and Spanish pimentón (dulce, agridulce, picante; the smoked versions are essential to chorizo).

11. Myths and confusions

Don't be confused: black pepper and chilli pepper are unrelated. Black pepper is Piper nigrum, an Asian vine whose heat comes from piperine. Chillies are New World Capsicum, and their heat comes from capsaicin. Columbus's mistake in naming them has confused the language ever since.

• "The heat is in the seeds." It is in the white placental membrane. Seeds are hot by contact.
• "Chilli causes ulcers." H. pylori and NSAIDs cause ulcers. Chilli can irritate an existing one.
• "Water cools the burn." It spreads it. Fat and dairy work.
• "Green peppers are a different vegetable." They are unripe versions of the coloured ones, with substantially less vitamin C and vitamin A.
• "Capsaicin burns fat." A real, tiny increase in energy expenditure. Not a weight loss tool.
• "Spicy food damages your taste buds." Desensitisation is a reversible change in pain receptors, not damage to taste.
• "Bell peppers are hard to digest." The skin is indigestible for some people; peeling or roasting solves it.

12. The bottom line

• Chilli heat is a receptor trick: capsaicin opens the channel that detects burning heat, so your brain reports a burn that is not happening. Birds are immune, which is exactly what the plant intended.
• The heat is in the white membrane, not the seeds, and it varies with variety, ripeness, and drought stress.
• Red and yellow peppers contain around three times the vitamin C of an orange, and eight times the vitamin A of green ones. Green peppers are simply unripe.
• Fat and dairy quench the burn; water spreads it.
• Topical capsaicin is a licensed neuropathic pain treatment, cohort studies consistently associate chilli eating with lower mortality, and the weight loss effect is real and far too small to matter.
• Wear gloves for very hot chillies, and never enter a chilli-eating contest.

Sources and notes

Composition figures are from USDA FoodData Central; production figures are approximate FAOSTAT values for the early 2020s. Capsicum domestication and the post-Columbian spread follow Kraft et al., PNAS, 2014, and Andrews, Peppers: The Domesticated Capsicums. Capsaicin content variation with water stress, temperature, and ripeness follows horticultural analyses. TRPV1 as the capsaicin receptor is Caterina et al., Nature, 1997, work that contributed to the 2021 Nobel Prize to Julius and Patapoutian. Bird insensitivity and directed deterrence is Tewksbury and Nabhan, Nature, 2001. Scoville and HPLC measurement follow ASTA methods. Vitamin C isolation from paprika by Szent-Gyorgyi is described in his 1937 Nobel lecture. Capsaicin desensitisation and licensed high-concentration patches for neuropathic pain follow the Qutenza product information and Cochrane reviews. Chilli intake and mortality follows Lv et al., BMJ, 2015, from the China Kadoorie Biobank, and Bonaccio et al.'s Italian Moli-sani analysis. Capsaicin and energy expenditure follows Ludy, Moore, and Mattes' meta-analysis. Milk and casein displacing capsaicin follows sensory science literature. The Carolina Reaper thunderclap headache case is reported in BMJ Case Reports, 2018.

Open questions. The chilli and mortality cohort findings are consistent across several populations and remain entirely observational, with obvious confounding by dietary pattern.

👉 Next: asparagus, celery, artichokes, and the odd vegetables.