The Science of Spiciness and Coolness
Capsaicin and Menthol
Spiciness and Coolness are not tastes in the strict sense, but sensations created by how certain molecules interact with the body’s sensory system.
Compounds like capsaicin and menthol activate receptors that normally respond to changes in temperature or irritation, producing the illusion of heat or cold.
The Heat of Capsaicin
Capsaicin, the pungent compound in chili peppers, creates the sensation of heat by binding to the TRPV1 receptors. These receptors normally respond to physical heat above 43C and to tissue irritation.
When capsaicin binds to TRPV1, it opens ion channels in sensory nerve endings, allowing calcium ions to enter the cells. This triggers the release of neurotransmitters that signal the brain to interpret the sensation as heat and pain, even though there is no actual rise in temperature.
The ‘spicy’ feeling is therefore not a taste but a pain response transmitted through the trigeminal nerve, which carries sensory information related to touch, temperature, and pain, from the mouth and the face.
The Cool of Menthol
In contrast, menthol, the compound responsible for the cooling sensation of mint, activates the TRPM8 receptors. These receptors are sensitive to temperature below 25C.
When menthol binds to TRPM8, the ion channels open and calcium ions flow into the nerve cell, sending a signal to the brain that mimics the sensation of cold. the mechanism is similar to that of capsaicin, but the sensory outcome is the opposite.
This last information can be quite interesting in the formulation of food and beverages.
The activation of the TRPM8 by menthol can happen at concentrations far below its odour threshold, meaning the cooling effect can be felt without adding a recognizable aroma of mint. In other words, you can induce a perception of freshness or temperature change without altering flavour.
At sub-threshold levels (where the mint aroma isn’t detected), the menthol can create a clean, cooling sensation that enhances the perceived freshness of a drink. You could make a Martini feel ‘colder’ a juice taste ‘fresher’, by adding tiny amounts (below 0.02-0.05ppm) of menthol.
This is the result of neural activity rather than chemistry in the glass: the mouth experiences a lower ‘felt temperature’ although the liquid itself is unchanged.
In short, both capsaicin and menthol activate the trigeminal nerve, adding sensation of temperature and pain that blend with taste and aroma to form the overall flavour experience.
While heat and cold are not basic tastes, they strongly influence how we perceive food and drink. The burn of chili, or the subtle chill of menthol, shows how chemical compounds and neural pathways work together to shape flavour beyond taste itself.