Spiciness is not a taste in the traditional sense, like sweet or sour. Instead, it is a sensation. This feeling arises from specific chemical compounds interacting with nerve receptors in the mouth and other mucous membranes. The body interprets this chemical interaction as a burning sensation, similar to how it would react to actual high temperatures.
Capsaicin: The Primary Culprit
Capsaicin is the most recognized chemical compound responsible for the heat in chili peppers. This compound is produced by the chili pepper plant, primarily in the placental tissue that holds the seeds and in the internal membranes. It acts as a defense mechanism, deterring mammals from consuming the fruit.
Capsaicin is a lipid-soluble, colorless, and odorless compound. It is part of a group of related compounds called capsaicinoids, with capsaicin being the most abundant. These compounds are alkaloids, unique to the Capsicum genus.
How Spiciness is Perceived
The sensation of spiciness occurs when capsaicin interacts with a specific protein receptor. This receptor is called Transient Receptor Potential Vanilloid 1 (TRPV1). TRPV1 receptors are activated by heat above 43°C (109°F) and acidic conditions, warning of potentially harmful temperatures.
When capsaicin binds to the TRPV1 receptor, it mimics the effect of high heat, causing the ion channel to open. This opening allows sodium and calcium ions to flow into the nerve cell, leading to a depolarization that triggers a signal to the brain. The brain interprets this signal as a burning sensation, even though no actual temperature increase has occurred. This mechanism explains why spicy foods feel hot.
Beyond Capsaicin: Other Spicy Compounds
While capsaicin is prominent in chili peppers, other distinct chemical compounds also cause pungency in different foods. Piperine is the primary pungent alkaloid found in black pepper, derived from the fruit bodies of Piper nigrum. When ingested, piperine initially may seem tasteless, but it soon produces a sharp, peppery, burning aftertaste. This sensation is also thought to involve the activation of TRPV1 receptors.
Another group of compounds, isothiocyanates, are responsible for the pungent sensation in foods like mustard, horseradish, and wasabi. Allyl isothiocyanate (AITC) is a well-studied example found in these plants. These compounds are not present in their native form but are produced when plant cells are damaged, allowing enzymes to convert precursor compounds (glucosinolates) into isothiocyanates.
Measuring Pungency
The heat level of spicy foods is quantified using the Scoville Heat Unit (SHU) scale. This scale was developed in 1912 by American pharmacist Wilbur Scoville. The original method, the Scoville Organoleptic Test, involved diluting a pepper extract in sugar water until a panel of trained tasters could no longer detect heat. The rating was based on the dilution factor.
However, the traditional Scoville Organoleptic Test is subjective, relying on human tasters whose sensitivity varies. Modern methods primarily use High-Performance Liquid Chromatography (HPLC) to measure pungency. HPLC objectively measures capsaicinoid concentration, providing a more accurate and consistent heat measurement. These analytical results are then converted into SHU. Bell peppers, containing no capsaicin, have a Scoville rating of 0 SHU, while extremely hot peppers like the Carolina Reaper can exceed 2 million SHU.
Coping with the Heat
Several remedies can alleviate the burning sensation from spicy foods. Dairy products like milk or yogurt are effective because they contain casein, a protein that binds to capsaicin. This binding washes away capsaicin, reducing its interaction with nerve receptors. Full-fat dairy is more effective due to its ability to dissolve capsaicin.
Sweet substances like sugar or honey also provide relief. Sugar may absorb capsaicin, while sweetness receptors might inhibit spiciness receptors. Starchy foods like bread or rice can help by acting as a physical barrier to absorb capsaicin molecules. Alcohol can dissolve capsaicin, offering temporary relief, but requires a high concentration (around 35%) to be effective; lower concentrations might spread it.