Chili Heat Hides in the Pith

The fiery sensation that chili peppers impart is primarily due to a chemical compound called capsaicin, which binds to pain receptors in our mouths, tricking the brain into perceiving heat. While many people attribute this intense burn to the seeds, the true source of a chili's pungency lies in the internal white spongy tissue known as the placenta, also referred to as the pith or ribs, where the seeds are attached. This placental tissue contains specialized glands that produce and store the highest concentration of capsaicinoids, the group of compounds responsible for the spice. The seeds themselves do not produce capsaicin, but they can become hot due to their proximity to these capsaicin-rich membranes.

From an evolutionary standpoint, the development of capsaicin in chili peppers, which originated in modern-day Peru and Bolivia, served as a defense mechanism. This chemical deters mammals, who typically chew and destroy seeds, from consuming the fruit (Review). Birds, however, are unaffected by capsaicin because their pain receptors do not respond to it. This allows birds to eat the peppers and disperse the seeds intact, aiding the plant's propagation. Capsaicin also offers protection against certain fungi and insects, further enhancing the plant's survival.

Humans, ironically, have cultivated chili peppers for thousands of years, appreciating the very "heat" that was intended to ward off other creatures. Early cultivation dates back to around 7,500 BC in the Americas, with widespread domestication in Mexico approximately 6,000 years ago. After Christopher Columbus encountered chilies in the Caribbean in the late 15th century, they were introduced to Europe and rapidly spread across the globe through trade routes, particularly by the Portuguese. Today, the varying levels of capsaicin in different chili varieties are measured on the Scoville Scale, a system developed by American pharmacist Wilbur Scoville in 1912.