Taste is fascinating, complex, and it turns out, very misunderstood. I love that the sense of taste was highlighted recently on both Science Live and picked up by Fox News online, but found myself editing the generalizations and inaccuracies in my head as I read on, who knew I was such a stereotypical scientist?
Here's the deal, and why I'm so jazzed up, taste is not flavor; this is a big misconception and one that is perpetuated in the recent taste articles. Many things contribute to FLAVOR (i.e. the sensory perception as you eat), smell, mouth-feel among others, and of course taste. But don't fall victim to confusing taste with flavor. We may say something "tastes" good, but what we really mean is that we like all the sensations that come together to make flavor. So no, texture and smell do not affect how we taste food, they affect how we perceive food as a whole.
We all know about the 5 tastes: salt, sour, umami, sweet and bitter. But what about the chance that there are more? I agree with Micheal Tordoff, a behavioral geneticist at the Monell Chemical Senses Center in Philadelphia, when he is quoted in the article, relaying his opinion that "There is no accepted definition of a basic taste. The rules are changing as we speak." In fact there was a great session that Dr. Tordoff led at the 2011 annual taste and smell meeting (Association for Chemoreception Sciences) called "Basic Tastes- Why Five?" This innovative session gave the podium to scientists pushing the limits on defining new tastes, and reiterated the rules we currently have in order to determine what is really a "taste" and what is not. While it's true that there is no 100% accepted definition, there are some basic guidelines that are pretty widely held concerning if a "taste" is really a "taste":
1. The is a evolutionary benefit to recognizing the taste (makes sense that we have it)
2. There is a defined stimuli that causes a person to identify the taste (there is a tired and true food/chemical that causes the taste)
3. There is a specialized transduction mechanism for the taste (how the tongue gets the info to the brain is unique to the taste)
4. The signal must originate and be conveyed by the taste system (i.e. the tongue and associated cranial nerves)
5. The taste must be perceptible and unique (you must actually taste it and it must be unique)
6. The taste must evoke a response (tasting causes a reaction… i.e. Yum! or Blech!)
That said, I agree with the fact that fat, calcium and maybe metal all may one day be considered true tastes. However, where I think there is a lot of debate surrounds the potential "tastes" that are really sensitivities by the trigeminal nerve, i.e. this cranial nerve has free nerve endings that are like live wires on your tongue and are the ones that help you detect texture (anything with mouth-feel), temperature (hot cold, mint etc.) and pain (capsaicin in hot pepper).
These are not the sense of taste, they are the sense of touch and are sent to the brain by the trigeminal nerve. There is so interesting new opinions on these sensations, but not a whole lot of scientific evidence that points at a new "taste". Taste is a part of the flavor experience, but taste is only one part and it is very distinct in how it works and what it helps our brains to understand about the world around us.
Final word, even if receptors exist on the tongue for a new "taste", if we are not conscious of the reaction, is it a true taste?