Taste and Flavour Facts
Sulekha Rani.R,PGT Chemistry,KV NTPC kayamkulam
Recent scientific research has revealed just how complex our sense of flavour really is. There is no single sense that defines flavour - although we perceive the flavour of food in our mouths, it is our brains that determine flavour. When humans evolved, we had to take whatever food we could - we ate berries and leaves or, when we could kill an animal, raw meat. It was essential to our survival to detect what food was safe, so we honed and evolved our senses to ensure we liked foods that were safe to eat and disliked those that were dangerous.
Our tongues have five different types of sensors (taste buds) - sweet, sour, salt, bitter, and umami (this last has only recently been recognised as a separate taste sensation - the taste of mono sodium glutamate, MSG - found in tomatoes, parmesan cheese and soy sauce, etc.). These are crucial. When we put food in our mouths, we need to decide whether to eat it or spit it out - this can be a life or death decision and needs to be made quickly. We need sugar as a source of energy - so we like sweet tasting foods - if all we taste is sweetness we will eat the food. We need salt to survive - salt has many essential roles - salt affects the electrical conductivity through the body - it governs how our hearts beat, how signals are transmitted along our nerves and in our brains, and controls many other processes.
Glutamic acid is one of the essential amino acids that form the building blocks of proteins - so recognising foods that provide it is important. It therefore not surprising that our "Umami" taste receptors are particularly attuned to the sodium salt of glutamic acid (mono-sodium glumate). Sourness often accompanies foods as they are going off due to bacterial action - think of sour milk - so recognising sourness helps us decide not to eat some foods. Most poisonous berries are taste bitter, so we need to recognise and dislike bitter foods. If we eat a bitter food we will not only spit it out, but follow that up by vomiting to get rid of any trace that may accidentally have got into our digestive systems.
But taste is just the last line of defence - we use all our other senses first - and these affect how we react to different tastes. First we look at the food - is it the "right" colour? Next we touch it - is it firm or soft? At the same time, we listen to how it sounds when we break it - is it crisp or soggy? Then we sniff it - are there any unpleasant odours? All these impressions tell us what to expect when we put food in our mouths. If we are eating berries, we will be looking for sweetness, combined with "fresh" and "tangy" aromas; if it is meat we will be looking for saltiness without any sour "off" aroma. The type of food and our memories of similar foods tell us the key aromas and tastes to look for in the "flavour". All this complex information is processed by our brains and interpreted as the "flavour" and is tasted in our mouths.
Our sense of smell is much more discriminating than our sense of taste. The organ we use to detect aromas is the olfactory bulb, located at the back of our noses near the middle of our heads. Inside the olfactory bulb, we have at least 700 different types of sensor and can use them to distinguish many millions of different molecules. It is not surprising that wine tasters sniff the wines first - their noses are attuned to look for a range of aromas that give clues to the grape variety and region, etc.
But how we use all this information is greatly influenced by the other senses. For example, if you taste a wine you will be influenced by its colour. Indeed, a recent experiment, fooled all the experienced wine tasters. In this experiment, the tasters were asked first to taste six white wines and describe the flavour. They described the flavours using words like "refreshing", "strawberry" and "citrus" to identify different notes in the aroma - these are words frequently used to describe white wines. Then when asked to identify the wines, the tasters were able to correctly identify the grape and the region - some even giving the exact vineyard and vintage.
Next a trick was played - the same six wines were served again, but this time with a little inert red food dye added. This time the tasters used completely different language to describe the flavour - "woody", "tannic" and "powerful" - all words associated with red wines. Then when asked to identify the wines, all plumped for red grape varieties and a few ventured opinions on actual wines they believed they had just tasted. However, when the experiment was repeated again - this time with the tasters blindfolded - they once again got the answers correct.
But there is much more to flavour perception than just the sum of all the different inputs from the eyes, mouth and nose. Our brains, it seems, respond much more to changes in which molecules are in the nose and mouth than they do to what is actually there, for example - if you chew a piece of gum, the flavour will disappear after a few minutes, as your brain gets "bored" by the aroma in the nose - but there is virtually no reduction in the amount of flavour molecules in the nose. However, if you simply change the input from your tongue, by, for example - taking a sip of sweetened water - the full flavour will be instantly restored. The area of flavour perception is one of the most exciting areas for scientific research - it holds out the promise of helping us find ever better ways to produce truly wonderful food.
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