08. WHERE'S THE SENSE IN THAT: TASTE THE DIFFERENCE

The final destination on our tour around the senses is TASTE. Your tongue is your chief organ of taste (or 'gustation' as it's also known), and if you've ever seen a close-up of the tongue, you'll know it's a jungle down there.

Our sensory guru Ian Francis has had his microscope out ...

Each taste bud on the tongue has a pore at the top, and little protrusions called microvilli from the actual taste cells pop through this pore. The taste buds are grouped into little bumpy regions on the tongue called papillae.

Different areas of the tongue seem to have different sensitivities to particular tastes, (sweet at the tip, bitter at the back, and so on), and it's thought that the shapes of certain tasty molecules in food fit into the nerve endings in the taste buds, in a 'lock and key' arrangement similar to how our sense of smell may work.

As well as sweet, bitter, sour and salty tastes, a fifth taste has been recently identified ('umami'), which is the sensitivity to savouriness like the monosodium glutamate added to many a Chinese take-away. The brain receives impulses from the nerve cells and makes the decision about whether the food is yummy and worth swallowing, or is foul-tasting and possibly bad for you, and should therefore be spat out.

The sense of taste is greatly affected by the sense of smell. When you have a cold, taste becomes hard to discern in food, and it's much more difficult to identify the taste of a mystery food if you hold your nose while you chew.

Every ten days about half of the taste receptor cells on the tongue are replaced, but as you age, the turnover decreases. This is why older individuals may have only half as many taste cells as younger people, and will therefore not taste as well.

Did you realise that food has to be moist for it to have a taste? You can test this by using a dry cloth to wipe your tongue and mouth free of moisture and then have a chew on a dry cracker. Not so tasty, huh?

Not everyone experiences tastes in the same way, and your ability to taste certain substances is genetic. For example, some people are unable to taste a substance called PROP whereas other find it exceedingly bitter and want to vomit. The non-tasters are missing a gene that codes for that particular taste receptor.

People with the best tasting abilities are officially called 'super-tasters'. US research suggests that around 35% of women are super-tasters compared to only around 15% of men. Super-tasting may also be linked with race.

But even human super-tasters are poor tasters compared to insects, which are some of best tasters of the animal world. Butterflies, for example, can taste sugar at concentrations 2,000 times lower than a human can ...