July 12, 2012

Taste Involves More Than Our Tongues

John Neumann for redOrbit.com - Your Universe Online

Every kid knows that we taste with our tongues, however those in the know, understand that this is a very rudimentary viewpoint. When it comes to flavor, the tongue is very basic. Most of our experience of flavor comes from our olfactory system: our nose and sinuses.

Professor Barry Smith, director of the Centre for the Study of the Senses at the University of London, explains, “Not only is it not just about your tongue. Very little of it is about your tongue.”

Taste, then, is the most mysterious of the senses, simply because it´s a collaboration between the other senses. The food industry is understandably interested in what scientists like Smith know about our perception of flavor, and how it can be manipulated. But there´s an awful lot they don´t know, reports William Leith of The Telegraph.

The tongue is able to determine five tastes — sweet, sour, bitter, salty and umami, which is the savory taste you get from meat, and also from monosodium glutamate. Taste experts have identified a new taste, metallic, which is a taste that exists in blood. Experts are not unanimous on that as of yet.

A “new” taste emerges after scientists identify previously unknown receptors on the human tongue that respond selectively to the taste in question. Of course, the sensation itself is not new. That was there all along. What´s new is that we have a better map of the tongue.

Another taste expert, Professor Charles Spence of the University of Oxford, who describes himself as a “neurogastronomist”, explains why we can taste these basic things on our tongues. We need to identify sweet things, because they are a source of calories, he says. Salt, umami and metallic designate protein.

Spence says that we can experience tens of thousands of flavors that involve our sense of smell. “But if I block your nose, there are only seven or eight distinct kinds of sensation.”

The main conduit for flavor is our olfactory system. Food goes in your mouth, and then down your throat. But your experience of it, your memory of that experience, goes up your nose and straight into your brain.

“Every smell begins with a molecule,” writes Molly Birnbaum in her excellent memoir Season to Taste. When you smell something, you are inhaling tiny particles of it into your nose. “With every inhalation,” says Birnbaum, “molecules travel through the thin craggy pathways that begin at the nostrils and head towards the brain.

They speed past the olfactory cleft, a narrow opening toward the top of the nose. They hit the olfactory receptors, which are housed on the hairlike tips of the millions of neurons that peek through a gold-hued mucous membrane called the olfactory epithelium.” We all have millions of these neurons. They are like wires leading to a sheet of bone, the cribriform plate, which Barry Smith describes as “like a switchboard”.

When the particles hit the receptors, the receptors take an instant reading of their chemical composition, and send this information through the switchboard, along the neurons, and into the brain.

It also turns out that our olfactory neurons are constantly wearing out and replacing themselves — until we get old, that is. As we get older, our olfactory neurons do not replace themselves so often, which is why old people often say their food doesn´t taste of much.

This explains why food doesn´t taste very nice on planes – the white noise of jet engines disturbs the olfaction process, so we effectively taste food as if we´re elderly. Using headphones can help.

It´s been known for the neurons to grow back and attach themselves incorrectly, leaving some people with the dreadful experience of smelling and tasting things all wrong. Sometimes, Barry Smith points out, a chocolate lover will find themselves hating the stuff.