Jalapeño peppers add a distinct level of heat to many dishes. The burning sensation they produce is not a flavor, but a chemical reaction in the mouth. This spiciness originates from capsaicinoids, with the most potent compound being capsaicin. Understanding this chemical-sensory interaction reveals why the jalapeño is simultaneously loved for its warmth and respected for its punch.
Capsaicin: The Source of the Sensation
Capsaicin is the primary molecule responsible for the jalapeño’s heat. It is an oily, colorless, and odorless substance, classified chemically as a vanilloid. Capsaicin is highly nonpolar, meaning it is incompatible with polar substances like water. This explains why drinking water offers little relief from the burning sensation, as the capsaicin will not dissolve and is simply spread around the mouth. The capsaicinoid family also includes related compounds like dihydrocapsaicin, which contribute to the pepper’s overall pungency.
The Physiological Mechanism of Burning
The sensation of burning occurs when capsaicin interacts with specific nerve receptors located in the mouth, throat, and digestive tract. This interaction targets the Transient Receptor Potential Vanilloid 1 (TRPV1) receptor, which is part of the body’s natural warning system. The TRPV1 receptor normally opens in response to actual heat (above 108°F or 42°C), trauma, or highly acidic conditions. Capsaicin is a chemical ligand that binds to this receptor, mimicking the effect of high heat.
When capsaicin binds to the TRPV1 receptor, it causes the ion channel to open, allowing positively charged calcium and sodium ions to rush into the nerve cell. This influx triggers an electrical signal transmitted to the brain. The brain interprets this signal as a burning sensation, despite no actual tissue damage or temperature change. Subsequent reactions, such as sweating and tear production, are part of the pain response triggered by this neurological deception.
Why Pepper Structure Matters
A common misunderstanding is that the seeds are the hottest part of a jalapeño pepper. Capsaicin is not produced in the seeds themselves, but in a distinct tissue inside the fruit. The highest concentration of capsaicin is found in the white pith or inner membrane, known as the placenta. This placental tissue is where the capsaicin is synthesized, and the level of heat correlates with the amount of this tissue present.
The seeds may feel hot because they are in close contact with the capsaicin-rich placenta and absorb some of the oil. Removing the inner white membrane is the most effective way to reduce the heat of a jalapeño, far more effective than simply scraping out the seeds. The distribution of capsaicin acts as a survival mechanism, deterring mammals that would chew the seeds, while birds, which are unaffected, can eat the fruit and disperse the seeds intact.
Measuring Heat with the Scoville Scale
The heat level of jalapeños and other chili peppers is quantified using the Scoville Heat Unit (SHU) scale. American pharmacist Wilbur Scoville developed the original test in 1912, called the Scoville Organoleptic Test. This subjective method involved dissolving dried pepper extract in sugar water and having human tasters dilute the solution until the heat was no longer detectable. The required dilution determined the pepper’s SHU rating.
Today, scientists use a more precise laboratory technique called High-Performance Liquid Chromatography (HPLC). The HPLC method directly measures the concentration of capsaicinoids in a pepper extract. This result is then converted into Scoville Heat Units, eliminating reliance on human subjectivity. A typical jalapeño pepper falls within a range of 2,500 to 8,000 SHU, placing it in the mild to moderate category compared to other chili varieties.