In this second portion on the science behind what we eat, we shall cover two main topics of Molecular Gastronomy research. If you missed Part 1, molecular gastronomy aims to study different aspects of food and cooking, from a scientific point of view. From cooking techniques to molecular components through to food psychology, scientists all over the world are demystifying our everyday eating habits. Now that we have been through the history of how this new subject came to be, let us concentrate on a specific field of research: neuroscience!
One question is on the tip of everyone’s tongue: what are taste buds and how do they work? Taste buds cover our tongues, allowing us to receive the taste sensation and transmit it to our brains. The buds can be found in taste pores – small opening on the tongue’s surface – and are usually flask shaped with a broad base and small neck-like opening onto the skin. There are around 100 cells of two different kinds in taste buds : supporting cells and gustatory cells. The supporting cells are thought to simply be a source of basic sensation while the gustatory cells (also known as chemoreceptors) are where it all happens. They usually sit at the centre of the bud and are spindle shaped. They have gustatory hairs at the top of them near the tongue’s surface and are innervated by the seventh, ninth and tenth cranial nerve. It is these nerves that will pass the information from your mouths to our brains.
But how does do these receptors, and then the brain, differentiate between the difference tastes we subject them to? The five different “taste sensations” have been defined as: sweet, bitter, savoury (sometimes referred to as unami), salty and sour. Although the myth goes that there is a map of the tongue, with different areas controlling different tastes; it is now thought that the taste qualities are spread all over the tongue, even if some regions may be more sensitive than more. With between 2,000 to 8,000 taste buds by tongue, how does the brain differentiate?
Now for some basic neuroscience. Different receptors in the taste bud cells are thought to be responsible for differentiating tastes. As most of us probably know, signals are transmitted to the brain via an electrical current coursing through nerves. There are many different ways of activating this current, most of which involve the transport of ions through a communication channel between cells and neurons. These channels are embedded in the membranes of cells and neurons and often link them together. The idea here is that different channels could “code” for different tastes. Salt and sour are supposedly measured by a flow of cations (positively charges molecules) through these channels. Sweet, bitter and unami and through to use a group of more elaborate receptors called GPCRs (G Protein Coupled Receptor) which are activated by the presence of particular proteins. Research into which specific receptors are responsible for which taste is still underway. For example, A taste receptor named TAS2Rs has been shown to be responsible for the ability to taste bitter substances.
Part of the reason for these receptors, like most things in our body, is the ultimate goal of keeping us alive. Our ability to “like or dislike” certain tastes were initially set up to protect us from eating poisonous foods and push us to consume those our bodies need to function. For example, we have a basic dislike of things that are sour, like some berries. This is probably because many berries are highly poisonous! And why do we like sweet things? Our bodies need glucose to maintain a level of activity, thus it pushes us to seek foods containing it. Although these rules may not apply in the modern whole we now live in, our taste buds had originally evolved to guide us to the right foods.
A little side note: why has unami (savory) only just been recognised in the West when it has always existed in Japan? Unami is meant to describe the taste of meat, cheese and mushrooms. The main substance we are detecting is called carboxylate anion of glutamic acid, an amino acid present in meats (particularly bacon). It can be used as a flavour enhancer, particularly its salt components. You might have heard of it being often used in Asian cooking – it’s called MSG. The reason we have only just started taking it into account, is that the separate receptors for unami were only discovered in 1996 at the University of Miami. Before that, it was only considered as a sensation mix of the other tastes.
The interesting thing about taste buds is that we can trick them. This is where psychology comes into play. It’s just a case of mind over matter. Many experiments have proven this in the past. Take for example, a group of wine buffs. They can supposedly separate various tastes in the wine they are drinking, from oak to cherries. They often comment on the texture and weight of the wine. A lot of this they can tell not only by smelling and tasting the wine but by looking at it. Thus a white wine will often be perceived as light and crisp with fresh fruit or citrus tastes. Red wine is heavier and dustier, maybe with the taste of berries. But what happens if you switch the wine colours? Experiments have been performed of transforming red wine to a white colour and vice-versa. The wine tasters where completely duped, analysing completely wrong associations in the wine simply due to the colour it showed. Other similar experiments have been made showing how our perceptions can alter our taste. Taste some ice cream. It takes… well ice creamy! Now taste it whilst thouching some velvet cloth: the ice cream will seem creamier. Taste some whilst touching some sand paper: the ice cream will feel gritty. How do we fool ourselves? These are some of the things scientists and chefs are trying to investigate within molecular gastronomy.
Although these concerns are of a more serious scientific nature, one particular aspect of their research might be very useful to your everyday meals. In a field where good cooking practice is all word of mouth and grandmothers hidden recipes, the molecular gastronomers are taking it into their own hands to rectify some basic cooking myths. For all you kitchen lovers, these have probably been drilled into your head (as they had mine), but have no scientific basis whatsoever. Myth number1: always add salt to water when cooking green vegetable. This one has an array of reasons: to keep the vegetables green, salting the water or heightening the boiling point. All untrue. The pigment in vegetables is not affected by salt but mainly by the acidity of the water (usually the calcium content). Adding salt to water does in theory increase the boiling point, but by a fraction of a degree. This is less than the difference between boiling the water at the top of a block of flats or at the bottom. Myth number 2: the cooking time for a roast is dependent on its weight. Now, any mathematician can probably work this one out. The point of timing a roast is to get it to a stage where the inside is as cooked (or uncooked depending on your tolerance for rare meat) as needed. The time it takes for the heat to diffuse to the centre of your roast is not dependent on its weight but on its diameter. Imagine chopping your roast into two segments along the width. The diameter would still be the same, thus the time it takes for the heat to reach the centre will not have changed. According to tradition, roast baking time would have been halved. And the best for last. Myth number 3: when making a meringue, if there is a spot of egg yolk in the egg white mix it will not rise. Every tried making a meringue? It takes some effort! Foody author Peter Barham rumanged through his cooking books and found a recipe for a different cake which also demands the whisking of eggs to stiff peaks. The recipe calls for egg yolks and whites. And it works. So don’t panic next time you get some yolk in your egg whites, it’s all a myth!