The pungency of chillies is due to a specialized metabolite, capsaicin, concentrated in tissues that surround the seeds inside the fruits. Capsaicin content is subjectively measured using Scoville heat units (SHU), i.e., how much a chilli extract must be diluted before its 'heat' is undetectable. Capsaicin contents vary from absent in bell peppers through jalapeño (2,500-5,000 SHU) and habanero (100,000-350,000 SHU) to extremes such as the 'Trinidad Moruga Scorpion' (2,000,000 SHU). Synthetic capsaicin is used in pepper sprays.
Capsicum is a small genus of approximately 25 species that, in pre-Columbian times, was restricted to the Americas. Five Capsicum species were domesticated in the Americas, although the regions of their domestication remain informed speculation: Capsicum annuum (bell pepper and jalapeño) in Mexico or northern South America; Capsicum frutescens (tabasco) in the Caribbean; Capsicum chinense (habanero and Scotch bonnet) in Amazonia; Capsicum baccatum (aji) in Bolivia; and Capsicum pubescens (rocoto) in the southern Andes. Domestication focused on the fruits; small, erect, deciduous red fruits of the wild forms were unconsciously selected to produce large, hanging, persistent, multi-coloured fruits. Along with these features came changes in capsaicin content and other compounds that give chillies their characteristic flavours. Although all five species contribute to the global spice trade, Capsicum annuum is the most important.
Chillies were cultivated and used in complex food cultures across the Americas from the Caribbean to the Andes six millennia ago, although they were probably harvested from the wild at least one millennium before this.
The first mention of chillies in western literature was by Diego Álvarez Chanca, physician on Columbus's second voyage in 1493, under the Taino name agi. The name chilli derives from the mainland Nahuatl name that the Spanish later encountered in Mexico in the 1520s. Interest in this new spice established itself rapidly across Europe. The first printed illustrations of chillies were published in the German botanist Leonard Fuchs' De Historia Stirpium (1543). By 1597, the English herbalist John Gerard reported that chillies were 'very well knowne in the shoppes at Billingsgate by the name of Ginnie pepper, where it is usually to be bought', although he had little success cultivating them.
Chillies spread rapidly to the Asian possessions of the Spanish and Portuguese Empires so that by the end of the sixteenth century it was established in China, India, Indonesia and Japan, whence it started to follow the trade routes from Asia back into Europe.
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