Food for thought

Researchers have identified the specific region of the brain that responds to pleasant tastes. Sanjida O'Connell reports on what this tells us about evolution, dieting... and beetroot jelly

Rice pudding is a truly horrific dish in Japan; apparently it's just too hard to swallow. Even in the UK, the creaminess or the rubbery skin can have some of us curling our toes. Taste is not a result of a few bumps on our tongue: new research shows how complex a sense it is. Our response to the taste and smell of food has far less to do with the basic building blocks of taste – bitter, sour, sweet and salt – and rather more to do with what is happening inside our heads.

Edmund Rolls, a professor of experimental psychology at Oxford University, has located the area of the brain that processes pleasant smells and has found that it differs from the region that responds to unpleasant ones. His lab has also discovered which part of the brain computes complex tastes – the orbitofrontal cortex.

Our perception of taste was turned on its head in the mid-Nineties with the discovery of a fifth taste, umami, the taste of protein, which is found in monosodium glutamate, as well as meat, cheese and mushrooms. Rolls' work is perhaps even more profound. He has shown that about 10 per cent of the brain cells in the orbitofrontal cortex are linked to our sense of taste. Some of these neurons respond to highly specific tastes – for example, there is one that reacts to salmon. Others will be triggered by several tastes. What is even more startling is that they are linked to our other senses – sight, smell, touch and even temperature.

A single neuron may respond to one taste or several, or to an array of senses; so a single brain cell could be triggered by the smell, the taste and the texture of a ripe strawberry. "This is very important," says Rolls, "as it allows you to code for a combination of different things. The number of stimuli we can respond to is very large."

Some neurons are genetically pre-programmed to respond to specific tastes and textures but the reactions of other brain cells are established as we develop a culinary repertoire unique to ourselves. And they're not set in stone, but can change over time. For example, putting salt on a raspberry will alter the taste. After eating 50 salted raspberries, the neurons that respond to the taste and texture of a raspberry will alter to accommodate the new flavour.

"As far as I am aware Edmund is in a league of his own in his research," says Heston Blumenthal, the chef and owner of the Fat Duck restaurant in Bray, who has embraced diverse scientific principles in his desire to push back culinary boundaries. Blumenthal gives an example from the Fat Duck's menu that shocked even him. He created a beetroot jelly.

"It's a pectin-based gel and it looks like an upmarket fruit pastille. Although it's made of beetroot it tastes of blackcurrant," he says. His pumpkin jelly tastes of orange, and the pale green fennel jelly of lime. Yet when he ate the sweets blindfolded, he could not distinguish them. They merely tasted sweet and slightly acidic. As soon as he took the blindfold off, the flavour rushed back in.

What's surprising about the science of taste is that in the accepted version of how this sense works, there was no way we seemed to be able to discriminate between the nutritional content of foods; this appears to be an evolutionary glitch. Rolls has discovered that we can tell when we're eating fat because specific neurons respond to the texture; since fat is so high in calories, being able to tell which foods were fatty would have been beneficial to our ancestors, who often lived on the verge of starvation. However, Rolls has found that people respond to fat only in liquid form; when it is disguised, in whipped cream for instance, our neurons do not respond. There is a clear warning here for weight watchers – eating foods that feel fatty will make us full faster than tucking into fat-rich foods that don't appear oily.

Rolls' latest research on smell also sheds light on an additional evolutionary benefit. When we smell pleasant foods, the orbitofrontal cortex and another area of the brain, the cingulate gyrus, are activated. Yet this response to the "hedonism" of food is processed separately from the way in which we determine the identification of a smell. As Rolls explains: "When I was in Japan I smelt wonderful fish in the Tokyo fish market. I wasn't hungry, but by responding to the smell it means that I can go back when I do feel like eating fish." This is therefore a mechanism for allowing us to learn about tastes and flavours without having to try them.

This same mechanism comes into play when we eat a meal. Because some neurons respond to specific smells, tastes and textures, if we eat only certain foods at a meal, they stop reacting and we start to feel full. The good news is that eating until our stomach is bulging is not the only way to feel replete – simply by doing what our grandparents told us and chewing carefully we can become satiated before that point.

The downside – at least if you're conscious of your weight – is that we're still keen to eat foods with new flavours. Rolls has shown that people who are given a variety of foods will consistently eat more than they would otherwise. Presumably this is the true success of anti-pasti – a medley of tastes, smells and textures that whets the appetite without causing satiety.

Blumenthal has already incorporated this research into the menu of the Fat Duck. "We register the rate of change of flavour," he explains. "The greater the jump between two flavours, the greater the impact. If you eat something that has a strong taste – such as soup made with basil – you'll quickly develop palate fatigue. But add coriander seeds, and your taste will be reinvigorated when you bite into one."

Rolls' most recent work, not yet published, is perhaps the most relevant of all to chefs. He gave people brain scans and found that their brains became more active when they ate the correct combination of food. For example, eating strawberries and sucrose, or chicken and umami caused a far greater response than eating strawberries and chicken on their own, or strawberries with umami.

"This shows us that it's worth exploring new combinations," says Rolls. "But it's difficult to predict how a new combination will strike us. It might initially have a novelty value, but in the long term it could become a combination that feels right." Perhaps Blumenthal's fried breakfast ice-cream and green tea and lime appetizer will catch on after all.