While we can detect countless flavors — each a combination of taste and aroma –, the standard explanation at the moment is that we can only detect five distinct tastes: sugar, sweet, salt, bitter and umami. The tongue is made up of receptors, each of which is “tuned” to one of these specific tastes. (Although the receptors aren’t perfectly evenly distributed across the tongue, neither are they grouped together in neat sections.)
Until now the most common assumption is that when we “taste” carbohydrates, it’s simply the result of them breaking down into less-complex chains of sugar molecule chains and thus we attribute their taste to sugary sweetness.
To explore an alternative explanation, Juyun Lim of Oregon State University led a study published in Chemical Senses. He found that test subjects who tasted a range of carbohydrate solutions were able to detect a specific taste that correlated to the length of carbohydrate chains (specifically glucose oligomers vs glucose polymers.)
Without any special treatment the subjects could taste both sweetness and what they most commonly described as “starchiness” or flouriness and likened to potato or rice, depending largely on ethnic background. When the subjects repeated the experiment with the addition of lactisole, which inhibits the tongue’s sweet receptors, they could no longer taste the sweetness but could still detect the starchiness.
Lim says it would make sense that humans had evolved to detect starchiness as a separate taste because it indicates food with slow-release energy.
The findings don’t necessarily mean starch will become widely accepted as a sixth taste. New Scientist notes most definitions of taste require that they not only be distinguishable and describable by the taster (which isn’t the case with another suggested “taste” named kokumi) but that they correlate to specific taste receptors, which isn’t yet the case for starchiness.