Red chilli

What a red chilli is

A red chilli is the ripe fruit of a plant in the genus Capsicum, in the nightshade family, Solanaceae. The fruit is botanically a berry: a thin wall around a hollow cavity, with seeds attached to a spongy placenta inside. Green fruits are the same pods picked early; as they ripen they turn red, and in some varieties orange, yellow, brown or purple. The word covers fruits that range from mildly sweet to hot enough to be painful, from a fat, thick-walled pod to a thin finger, and from a pod eaten fresh to one dried for months.

What a cook buys under the name comes in four main forms. Fresh red chillies are used whole, sliced or blended into pastes. Dried whole pods are toasted, soaked or ground. Flakes are crushed dried pods, usually with seeds. Powder is dried fruit ground fine; it may be a single chilli or a blend. These forms behave differently in a dish, and a recipe that says "red chilli" without saying which one leaves the cook to decide. A fresh pod adds moisture and a green-vegetal brightness as well as heat; a powder adds concentrated colour and flavour but no water.

Flavour in chillies is more than heat. Fruity, smoky, sweet, earthy or floral notes depend on species, variety, ripeness and how the pods were dried. The same plant can therefore supply a sharp green condiment and a deep red spice, depending on when it is picked and what is done to it afterwards.

Species and heat

The genus has about 25 species and was restricted to the Americas before Columbus. Five of them were domesticated there. Capsicum annuum includes the bell pepper and the jalapeño and is the most important species in the global spice trade. C. frutescens gives the tabasco pepper. C. chinense includes the habanero and the Scotch bonnet. C. baccatum is the aji of the Andes, and C. pubescens is the rocoto. The regions where each was first domesticated are, in the words of one botanical profile, still "informed speculation".

Heat is measured in Scoville heat units, which record how far a chilli extract must be diluted before the burn can no longer be tasted. Bell peppers contain no capsaicin and measure zero. A jalapeño is usually quoted at 2,500 to 5,000 units, a habanero at 100,000 to 350,000, and the hottest bred varieties go beyond 2 million. These are ranges, not constants: a single variety varies with growing conditions and ripeness, and the colour of a pod says nothing about how hot it is. In general smaller pods are the more pungent.

Breeders and growers have named hundreds of selections within each species. The Tamil Nadu Agricultural University lists annuum varieties by habit and fruit shape and says which suit green harvest, red-ripe harvest or drying. The variety CO.1 is a reselection of the local Sattur Samba type, CO.2 comes from a Gundu type of Erode district, and CO.4 is recommended for chutney, curry and pickles. The point for the kitchen is that "red chilli" is a category of use, not a variety, and a recipe from one region implies a different pod from the same recipe in another.

Domestication in Mexico and the Americas

Chillies were cultivated in the Americas about six thousand years ago and were probably gathered from the wild for at least a thousand years before that. Domestication turned small, erect, deciduous red fruits that dropped from the plant into larger, hanging, persistent fruits in many colours, and it changed the capsaicin content and flavour compounds along the way.

A 2014 study of the origin of Capsicum annuum combined genetic, archaeological, ecological and linguistic evidence. Taken together, the evidence pointed to central-east Mexico as the place of domestication; the genetic data alone favoured an area further north. The authors treat the result as a model, not a proof. Some archaeological pepper remains are dated by the layers they lie in rather than by direct measurement, so no one can name a precise first field or year.

Other species had their own histories further south: the habanero type in Amazonia, aji in Bolivia and the rocoto in the southern Andes. Chilli was already a standard seasoning from the Caribbean to the Andes when Europeans arrived.

How the chilli crossed the world

The first mention of chilli in western literature is by Diego Álvarez Chanca, physician on Columbus's second voyage, in 1493, who wrote the Taino name aji. The Spanish met the Nahuatl name, from which "chilli" derives, on the Mexican mainland in the 1520s. Leonard Fuchs printed the first European illustrations in 1543, and John Gerard reported in 1597 that chillies were sold at Billingsgate as "Ginnie pepper". By the end of the sixteenth century they were established in China, India, Indonesia and Japan, and from Asia they travelled back into Europe along trade routes.

Gonzalo Fernández de Oviedo, writing about the Indies in 1535, describes aji as a cultivated seasoning eaten with fish, meat and other foods. He notes elongated and rounded fruits, different colours, kinds eaten before ripening and a kind that could be eaten raw without burning. His picture is of a diverse crop, not a single hot red pepper.

Chilli was often called "pepper" in European and Asian languages, which makes the early record hard to read. The historian Stefan Halikowski Smith shows that the two plants moved through markets differently, and questions the popular story that gives a particular Portuguese governor the credit for bringing chilli to India. A fair account says that the chilli was adopted quickly and widely, through several routes, in the sixteenth century.

Why the fruit is red

The colour of a ripe chilli comes from carotenoid pigments made in the fruit's chromoplasts, plastids that replace the green chloroplasts as the fruit ripens. Yellow and orange fruits owe their colour mainly to alpha- and beta-carotene, zeaxanthin, lutein and beta-cryptoxanthin. The red is made by pigments found almost only in Capsicum: capsanthin, capsorubin and capsanthin-5,6-epoxide. Which carotenoids a fruit makes, and how much, depends on variety and growing conditions, which is why two red chillies can differ in depth of colour.

Colour is a major reason cooks use chilli in preserved foods. Red powder and paste colour sausages, pickles, sauces and kimchi, and the pigments are fat-soluble, so they carry into oil. They are a separate quality from heat: a deeply coloured pod can be mild.

Where the heat comes from

The burning sensation comes from capsaicin and related capsaicinoids, which bind to a heat-sensing ion channel on pain-sensing nerve cells. This receptor, identified in 1997, also responds to temperatures above about 43 degrees Celsius, which is why a chilli feels hot rather than merely irritating. Capsaicinoids are concentrated in the tissue around the seeds. In a study of ripe Tabasco peppers, the placenta had the richest capsaicinoid content of the tissues tested, and the seeds and the outer wall had different chemical profiles. Because the heat is concentrated around the seeds, cutting away the placenta and seeds removes much of a pod’s pungency, though seed removal alone does not tell the cook how much heat is left.

Pungency is a sensory response with real physical effects. Capsaicin irritates skin, eyes, the digestive tract and airways, and oil carried from hands to the face turns routine cutting into a painful exposure. The advice from poison-control specialists is to wear gloves, work in a ventilated space and avoid touching the face after handling hot peppers. Cooking or grinding hot chillies can put irritating vapour or dust into the air.

Fresh, dried, flakes and powder

The international standard for fresh chilli peppers covers commercial varieties supplied fresh to the consumer. Its quality criteria are plain: whole, sound, firm, clean fruit, free from deterioration, and developed suitably for the variety. Chillies for industrial processing are outside its scope. Those criteria are a good guide to buying fresh: glossy, firm skin without soft spots, mould or shrivelling.

Drying is one of the oldest ways to preserve chillies. Extension guidance for drying chile makes two points that apply to any pod: moisture has to be removed as quickly as possible at a temperature that does not seriously damage flavour, texture and colour, and if the temperature is too low at the start, microorganisms can survive and even grow before the food is dry. Mould spreads quickly in drying pods and releases spores even when dry. Moisture left in a pod invites mould, so a dried pod should be fully dry before it is stored.

Powder and flakes are convenient but are less transparent. A powder can be a single chilli or a blend, may contain seeds or stems, and shows less of its origin. Dried spices are not sterile. The US Food and Drug Administration's risk profile names Salmonella as an important hazard in the spice supply, with evidence from imported and retail spices. A dry, pungent ingredient is not automatically safe, so a spice that will not be cooked afterwards should come from a supplier who can say how it was treated.

What red chilli does in fermentation and preserving

Chilli contributes in four ways to a ferment: colour, flavour, fermentable sugar and an influence on which bacteria thrive. It is rarely the main substrate, but it changes the character of what it joins.

In kimchi, red pepper powder is a standard seasoning, and a 2024 study tested its pungent compounds directly. Five batches of kimchi were made with capsaicinoid levels from 4 to 50.3 mg per kilogram and held at 4 degrees Celsius for 28 days. The capsaicinoids did not break down during that time. Starting at pH 5.36 to 5.52, all batches except the highest fell below pH 4.0. The amount of capsaicinoid did not change the bulk pH or acidity much, but it changed how the lactic acid bacteria grew, with differences in the free sugars, amino acids and bacterial succession that followed; one effect was more mannitol, a sugar alcohol made by heterolactic bacteria from fructose, at higher capsaicinoid levels. So chilli acts less like a switch that stops fermentation than like a nudge that shifts which organisms lead it.

Hot sauce makers ferment red pepper mash in barrels with salt for anywhere from two weeks to three years. In an 18-month study of such a mash, the pH fell steadily as acid accumulated, lactic acid bacteria and yeasts grew together throughout, colour changed only a little, and six aroma compounds rose significantly in the first 60 days before falling by day 300. Mash is a good substrate because the fruit is rich in sugar and, once crushed and salted, gives up its juice.

A 2022 study mashed fruit from six cultivars of Capsicum annuum and Capsicum chinense, including wall, placenta and seeds, and followed spontaneous fermentation, measuring chemical changes and the lactic acid bacteria and Leuconostoc populations. It shows that pepper mash supports microbial activity under defined conditions. It does not make chilli a preservative, and a claim about a finished pickle or paste needs evidence about its own salt, acidity and storage.

Fresh and dried chilli are also added to pickles, chutneys and oil preserves in which no fermentation of the chilli is claimed. In a Himalayan pickle of galgal, a hill lemon, the ingredient list calls for 8 to 12 red chillies and the method uses red chilli powder; the pickle is rested in a jar. Chilli in such a pickle adds colour and heat, and the form used, fresh or ground, changes how much moisture and flavour it brings.

Choosing and storing red chilli

For fresh chillies, choose firm, glossy, evenly coloured fruit with the stem attached and no soft patches. For dried pods, look for even colour and no mould or musty smell; for powder, look for a deep, even colour and a clean smell. Buy from a traceable supplier and keep the product information, since a powder or flake cannot show its own origin.

Keep dried pods and powders dry, since moisture is what lets mould grow in them. Fresh pods can be dried with attention to the points above. No source used here gives a shelf life for chilli, so none is stated.

Hot chillies need handling care. Wear gloves for cutting, wash hands and equipment afterwards, keep fingers from eyes and face, and ventilate when grinding or cooking.

Allergy and dietary context

Capsicum can cause a true immune-mediated food allergy, quite separate from the burn of capsaicin. A clinical report on a patient reacting to bell and chilli pepper identified a Capsicum protein, Cap a 7, a gibberellin-regulated protein that cross-reacts with a protein of Japanese cedar pollen. The report shows that such reactions occur; it is not a measure of how common they are. A person with a diagnosed Capsicum allergy needs individual advice, and removing seeds or choosing a milder variety does not make a product safe for them. Chilli has no gluten, but a purchased powder or paste can contain other ingredients, so the label matters.