Can science make food taste better? The tongue is able to determine five tastes - sweet, sour, bitter, salty and umami, which is the savoury taste you get from meat, and also from monosodium glutamate. Smith tells me that taste experts have identified a new taste, metallic, which is a taste that exists in blood. The jury is still out on an additional taste, fatty acid, which is yet to be confirmed. 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. Bitter things should mostly be avoided - most toxins are bitter; we need to identify them so we can spit them out. Sour things can be good or bad, depending on how sour they are. Spence says that we can experience tens of thousands of flavours that involve our sense of smell. But if I block your nose, there are only seven or eight distinct kinds of sensation. Smith tells me to do an experiment on myself. Put a flavoured jelly bean in my mouth with one hand, and block my nose with the other. Chew on the bean. What does it taste of? Nothing much. Then unblock my nose. A real hit of fruit. The difference is amazing. He and Spence have worked as consultants to companies such as Courvoisier, which makes brandy, and Mumm, which makes champagne. What they actually do sounds quite rarefied; for instance, trying to work out if listening to music affects the way you experience brandy. Apparently it does, because certain types of music make us more receptive to certain aromas; high piano notes enhance our reception of citrus, and low brassy notes bring out bitter aromas such as coffee. Spence has conducted experiments in which people are asked to chew stale Pringles. They taste stale. But when you chew stale Pringles and simultaneously listen to the amplified sound of your own crunching on a set of headphones, you think the stale Pringles you're chewing are fresh. Similarly, if you taste ice cream with a hint of bacon flavour, it tastes much more bacon-y when you listen to the sound of bacon being fried. That's another one of Spence's experiments. A third showed that people tend to prefer seafood if they can hear the sound of sea birds and crashing waves. "People think food tastes so much better on holiday," says Spence. And then when they bring it back, it doesn't taste the same. But it's not about losing flavour in the aeroplane hold. Our experience of flavour, then, is about all sorts of things. It's about where we are when we eat something. It's about the occasion. It can even be about the price - we've all heard of wine drinkers who "taste the price." Sometimes people appear to taste food or drink according to its colour, and that's why Tab Clear, a colourless cola launched by Coca Cola in 1992, failed to impress consumers. People didn't think they were tasting the caramel flavour, because their eyes told them they weren't; it was withdrawn two years later. This is also why, in experiments, people think red drinks are sweeter than green ones, even if the only difference is the colouring in the liquid. Other factors come into play, such as one's general health, and whether or not you're happy. One thing is for certain - the main conduit for flavour is our olfactory system. Food goes in your mouth, and then down your throat. But your experience of it - and your memory of that experience - goes up your nose. One day recently, my son offered me a crunchy potato snack. I couldn't remember when I'd last eaten one, and when I popped it into my mouth, and felt it disintegrate, something strange happened. I was transported back to the Seventies, to a tuck shop, to a bustling queue of elbowing boys; I felt the emotions, good and bad, of a moment from my boyhood. I was taken back in time, and also forward. It was a powerful thing. "A Proustian moment," I thought, remembering the scene in Marcel Proust's novel Remembrance of Things Past, in which the narrator takes a bite of a madeleine cake and is immediately transported to his own childhood. As my Proustian moment passed, I wondered if the food industry has somehow learned to tamper with our memories. "Every smell begins with a molecule," writes Birnbaum in her excellent memoir Season to Taste, which was published last year. 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. When Molly Birnbaum's head made contact with the car's windshield, the front of her brain hit against her cribriform plate. The neurons leading from the brain to the plate were shorn off. That's why she couldn't smell, or taste, the apple pie. Her olfactory circuit had been broken. How much of our experience of flavour is olfactory? "About 80 per cent," says Smith. Molly Birnbaum agrees. In case you're curious, this doesn't mean that people who lose their tongues can taste much - the tongue may not be the main engine of flavour, but sensors on the tongue provide a trigger for the whole process. But how, I ask Barry Smith, can a few molecules from a mouthful of food connect directly to the memory? How can one bite of a crunchy potato snack take me right back to my childhood? The relationship between smell and memory - and, therefore, between flavour and memory - is an interesting one, Smith tells me. For one thing, we have a very poor olfactory imagination. We can't actually conjure up smells in the mind in the way we can conjure a painting, or someone's face, or a piece of music. "Our capacity to imagine smell is not very good," says Smith. But olfaction is the only one of the senses that's not gated by the thalamus. What he means by this is that when we see something or touch something, a signal is sent to the thalamus, where it can be analysed, after which it is routed to the amygdala, the seat of our basic emotions. But when we smell something, it's not processed at all on the way to the amygdala. With smell, we get an instant hit. And when we crunch into a snack we haven't eaten for years, we feel an instant emotion. That's why a crispy snack can take you back to your childhood. And that's also why, if you got drunk on peach schnapps or cherry brandy as a teenager, a single sip of one of those drinks, or even a sniff, will make you want to gag. Neurons are making an instant chemical reading, and sending a message straight to the part of your brain that remembers that first hangover. And now for something a bit more scary. Birnbaum points out that when several women live in the same house, their periods tend to align. This might be because of pheromones - particles sprayed out into the air, containing information about hormones. Very little is known about how they work, but they're clearly very powerful. And the thing about pheromones is you can't smell them. Or rather, you don't know you're smelling them. But, if you are, they go up your nose, and then they affect your behaviour on a subconscious level. We know the food industry is able to create artificial flavours, building them from combinations of chemicals. As Birnbaum explains, isoamyl acetate smells very like bananas. Benzaldehyde smells of marzipan. Now, though, the industry is becoming aware of the relationship between food and sex; Birnbaum has met a chemist called Marie Wright who works for an American company called International Flavours and Fragrances. Wright has created a flavour she calls "orgasm" - a mixture of chocolate and something "musky." This is just the start. Pam Dalton, of the Monell Chemical Senses Center in Philadelphia, has conducted experiments in which people are given ice cream impregnated with vanilla they can't consciously taste. Even so, it sends a vanilla signal to the brain, making the ice cream taste sweeter. Interestingly, Birnbaum points out that Ben Cohen, the co-founder of Ben & Jerry's, was born without a sense of smell - he stuffed extra ingredients into his ice cream to make it more appealing. Lacking a sense of smell, Molly Birnbaum had to abandon her plans to become a professional chef and says she suffered from a "slow, creeping depression." Smell had connected her to the world in all sorts of ways. Without it, she felt frightened and lost. She found she'd lost the ability to cook and began to "dread" eating. But after a few years of sticking herbs up her nose in a bid to kick-start it, something happened. Birnbaum's sense of smell - and also her sense of flavour - began to come back. At first, she could smell certain herbs. Then she could smell the yeasty aroma of bread. Walking along the street one day, she even felt overjoyed at the smell of rubbish. It turns out that our olfactory neurons are always 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 is 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. Luckily, Birnbaum's neurons grew back just fine. Though she's "not entirely positive" her taste is what it once was, she no longer dreads eating.