A gel-based artificial tongue can determine the spiciness of a wide range of foods, from the forgiving bell pepper to the formidable ‘facing heaven’ chili of Sichuan cuisine.

The device, as the researchers report¹inACS Sensorsmight be the secret to determining the heat levels of spicy foods without risking any human taste buds.

The artificial tongue itself is not a new feat. Scientists have created similar devices that can use electronic sensors to detect sweetsour, spicy and umami tastes. But the authors of the new paper wanted to focus on spiciness in particular and to measure spice levels as precisely as possible, which is especially important for quality control in food, says co-author Jing Hu, a chemical engineer at the East China University of Science and Technology in Shanghai.

Taming the burn

The team’s solution was “inspired by the spicy-neutralizing effect of milk”, they write in the paper. Milk “proteins that affect our perception of spiciness” relieve the burn of a spicy dish, explains Carolyn Ross, a food scientist at Washington State University in Pullman.

The synthetic tongue is made of a gel that contains milk powder, acrylic acid and choline chloride. When a current is applied to the gel, its chloride and hydrogen ions can conduct electricity because they are mobile. To monitor changes in conductivity, the scientists placed the gel between copper sheets and connected the whole contraption to a workstation that measures the electric current.

Capsaicin — the compound that gives chilli peppers their spice — interacts with the milk proteins in the gel to form bulky complexes that disrupt ion flow. As a result, when the tongue encounters capsaicin, its conductivity drops.