Wow! Except here's what's in the body of the story
For sweet tastes there is a channel called TRPM5 which is temperature sensitive, so people taste more sweetness when the food is hot than cold. So to mimic sweeter tastes the device changes the temperature of the tongue rapidly from 77F (25C) to 104F (40C.)
So it warms up the tongue just a bit to make some foods taste sweeter. What a let-down.
"The team say that they are also working on producing different tastes which they claim is time consuming because even the difference between a lemon and a lime is vast."