10 scientific facts about flavour

As a learned journal brings together research findings about how we taste, Clint Witchalls looks at what scientists have discovered so far.

Taste is fairly well understood. It is detected by the tongue and is neatly categorised into sweet, bitter, sour, salty and umami. If food was only experienced as taste, chefs and restaurant critics would be out of a job. Luckily, taste is only one facet of the complex thing we call flavour.

Flavour is, of course, the stock in trade of chefs. For centuries, they have been combining flavours to create something that is more than the sum of its parts. From a scientific point of view, however, flavour is not that well understood. Although there has been a drip-feed of research over the years, there has been no cohesive effort to study flavour as a discipline.

That has just changed. BioMed Central, publishers of open access science journals, launched a new title last month: Flavour. For the first time, there will be a forum for flavour research, whether you're a biologist, a chemist, a neuroscientist, a psychologist, an anthropologist or even a philosopher. Unlike most science journals, which are aimed at a narrow group of specialists and are all but indecipherable to everyone else, Flavour hopes to appeal to a much broader church, including chefs.

Before the research starts pouring in, here is a quick run down of some of the things scientists know about flavour.

'Flavour' is published by BioMed Central (biomedcentral.com)

1. Flavour is evolution's way of making sure we eat a varied diet

This is because we need certain nutrients in order to survive. "There needs to be ways of guiding us through to ensure we get enough of these macro and micro nutrients," says Per Moller, editor-in-chief of Flavour. "Nature solves that problem by endowing us with the ability to sense flavours of food."

Different macronutrients tend to have different flavours. Bread and potatoes and pasta are more similar than different meats are. "If you eat potatoes, after a couple of hundred grams you won't like the potatoes quite as much as you did when you started eating them," says Moller. "So there is a decline in the liking of the thing you have eaten a bit of, but without a decline in liking of other foodstuffs." Or, in science-speak, we possess neuro-biological systems that are sensory-specific satiety mechanisms. "Luckily, we don't need a degree in nutritional science to get a balanced diet," quips Moller.

2. We don't just sense flavour with our tongues

Taste, smell, touch, sight, sound, temperature, trigeminality (the irritating component of odour, as experienced when eating a chilli or horseradish), and interoception (stimuli arising inside the body) are all involved in creating the sensation in our brains that we call flavour.

3. Colour affects how we perceive flavour

Red wines are usually described in terms of red or dark objects and white wines in terms of light or yellow objects. The Independent on Sunday's wine expert, Terry Kirby, described Sequillo 2008, a blended white wine, as tasting of "straw, nuts and honey", and Lirac Clos de Sixte 2006, a blended red, as tasting of "spices, dark chocolate and black fruits". Had those wines been decanted into opaque glasses, even Kirby might have described the flavours differently. Researchers at the School of Enology at Bordeaux University found that when students were given white wine, tinted red with a flavourless additive, and asked to describe it, they tended to use adjectives usually reserved for red wines.

4. Coffee tastes worse in a flimsy cup than a substantial one

Researchers at Rutgers University and University of Michigan found that the firmness of a cup influences people's perceptions of taste and quality. Give them the same beverage in a firm cup and they will prefer the taste to the beverage in a flimsy cup. The subjects were also divided into groups who like to touch things before they buy them (high autoletics) and people who don't like to touch before they buy (low autoletics). Oddly, the people who touch everything when out shopping are least influenced by touch in taste evaluations.

5. Even how food is described can affect its flavour

Protein bars taste less good if they are described as soy protein and yoghurt, and ice-cream is perceived to be more flavoursome when described as full fat or high fat.

6. There is no such thing as a 'tongue map'

The human tongue does not have distinct zones for discerning sweet, bitter, sour, salty and savoury tastes. The so called "tongue map", often seen in primary school textbooks, is based on dodgy research published in 1901 by a German scientist named DP Hanig. Despite the science being debunked back in 1974, some wine-glass makers still make spurious claims that this or that shaped glass will draw wine to a specific part of the tongue. Taste buds actually have 50 to 100 receptors for each taste, including umami (the taste of glutamate).

7. Some people have many more tastebuds than the rest of us

They are called super-tasters. That doesn't mean they're connoisseurs, it means they're very sensitive to bitter tastes. Do you hate the taste of Brussels sprouts? You may be a super-taster.

8. Although it's yet to be utilised, the smell of food matters

Aroma is an extremely important component of flavour and it is detected by receptors in the nose (orthonasal) and the mouth (retronasal). You might think that the brain treats both of these signals the same, but scientists have found, using fMRI brain scans, that different parts of the brain are stimulated depending on whether the aroma is detected by the nose or the mouth. What this means for chefs, though, is not clear yet.

9. Aroma affects the amount of food we put in our mouths

Scientists in the Netherlands developed an experiment where a "custard-like dessert" was fed to volunteers while different scents were presented to their noses. The research, published in the inaugural issue of Flavour, reported that strong aromas lead to smaller bites, suggesting that aroma could be used to control portion size. Forget the fat tax, what we really need are strongly flavoured fast foods.

10. Our liking for flavours develops before birth

A recent study took 24 pregnant women and divided them into two groups. One group was given a diet containing anise, and the second group was given an anise-free diet. Shortly after the babies were born, they were presented with cotton soaked in anise. The babies whose mothers had consumed anise during their pregnancy showed no aversion to the swab, while the babies whose mothers had avoided anise showed a strong aversion to the aroma.

Unanswered questions

One thing science hasn't answered yet is why some flavour combinations work while others don't. One theory is that there is a chemical overlap between flavours that work well together. Heston Blumenthal's unlikely combination of white chocolate and caviar is said to work well because both ingredients contain trimethylamine.

But, it turns out the flavour-sharing hypothesis doesn't have legs. Yong-Yeol Ahn, of Harvard University, and colleagues did a statistical analysis of 56,000 recipes from various regions and found that, indeed, there is a tendency in North American and Western European cuisine to use ingredients that share many flavour compounds.

However, the researchers found that Southern European and East Asian cuisines tend to avoid compound-sharing ingredients, yet few would argue that these regions don't produce delicious food. So we're still none the wiser as to why we like certain food combinations and not others.

But if food is essential to our survival, why did evolution endow us with a dislike for, say, strawberries and liver? Scientists, please send your answers to Mr Moller.