If you had to pick one adjective to describe a glass of water, it is unlikely that the first word to pop into your head would be flavoursome.
But now scientists have confirmed that the old H2O does actually have a distinct flavour, and a sour one at that.
A team from Caltech, led by associate professor Yuki Oka, found that water should actually be classified as a sixth taste – independent from the basic five officially recognised by taste buds – sweet, sour, salty, bitter and umani.
Oka said: “The tongue can detect various key nutrient factors, called tastants— such as sodium, sugar, and amino acids—through taste, however, how we sense water in the mouth was unknown.
“Many insect species are known to ‘taste’ water, so we imagined that mammals also might have a machinery in the taste system for water detection.”
Taste cells relay information about tastants to the brain via nerves called the taste nerves, which scientists know are stimulated by different flavours.
But the most recent study in mice showed that the tongue of mammals was also stimulated by pure water.
Graduate student Dhruv Zocchi, said: “This was exciting because it implied that some taste cells are capable of detecting water.”
Once it had been established that the tongue was responsive to the presence of water, they then blocked the function of individual cell populations to work out which of the taste buds were reacting.
“To our surprise, when we silenced sour taste cells, water responses were also completely blocked…the results suggested that water is sensed through sour taste cells,” said Oka.
The team suggested that as water is so integral to our survival, it makes sense that we can identify it as a unique flavour.