Squirty gels bring the taste of cake and coffee to virtual reality

Imagine seeing cake in a virtual world, then tasting it. Researchers have taken a step toward that reality with a device that delivers virtual tastes by squirting chemicals onto the tongue.

The system, called “e-Taste,” can detect chemicals in foodstuffs and wirelessly transmit this information to a device that delivers the same or equivalent chemicals to a user’s tongue. By combining different chemicals, the device can mimic flavors ranging from cake to coffee, researchers report February 28 in Science Advances.

“This is a step towards the next generation of human-machine interfaces and virtual reality,” says materials engineer Yizhen Jia of Ohio State University.

The system uses five edible chemicals: glucose for sweet, citric acid for sour, sodium chloride for salty, magnesium chloride for bitter and glutamate for savory umami. These chemicals are infused into gels inside the device, which get mixed in tiny channels. An electromagnetic pump delivers the mixture to the tongue via a flexible, ribbonlike conduit inserted into the mouth.

To evaluate e-Taste, Jia and colleagues first had 10 participants distinguish between five intensities of sourness produced by the device. The researchers then created five complex tastes — lemonade, cake, fried egg, fish soup and coffee — based on their chemical compositions. Six participants were trained to recognize these flavors, achieving an overall accuracy of nearly 87 percent. Some tastes, such as lemonade and cake, were easier to identify than others, such as fried egg.

Previous efforts have attempted to simulate taste through electrical stimulation of the tongue, but this method remains poorly understood. “We don’t have a hundred percent understanding of how the tongue and taste perception works,” says Nimesha Ranasinghe, a computer scientist at the University of Maine in Orono who was not involved in the study. “Taste and smell, being chemical senses, are very challenging.” Chemicals, for now, can reproduce a wider range of tastes than electrical stimulation.

However, taste alone is not enough. “Real coffee comes with the smells and feeling of coffee,” Jia says. “Only putting chemicals on your tongue isn’t going to be comparable.”

To help bridge that gap, Jia and his colleagues are working to incorporate smell using gas sensors and machine learning. The team envisions applications in immersive gaming and even sensory rehabilitation, such as for individuals who lost their sense of taste due to COVID.

Perhaps the biggest unknown is how willing people will be to wear a device that squirts chemicals onto their tongue. “We are very reserved when it comes to putting anything inside our mouth,” Ranasinghe says. “The look, feel and comfort are really important. It’s a major aspect of this people have to look into in future.”