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Well, four of course - most people will probably say - namely bitter, salty, acid and sweet. For decades, this was considered the last word in wisdom. But in fact there are more - because already in the 1990s a fifth was scientifically recognised - namely "umami".

Recently, a sixth taste direction was discovered - namely "fat". This should by no means be confused with the Austrian dialect expression for the state after excessive alcohol consumption. It actually refers to the (scientific definition) "mixed esters of glycerol and higher carboxylic acids with an even number of carbon atoms". So, for example, "the white" in a fat roast pork.

And still no end. For recently, at least once, a seventh taste was recognised as a thesis - namely water, which (allegedly) tastes "like nothing". But the "nothing" is also a taste, according to scientists who studied the phenomenon.

The sense of taste

The sense of taste is the ability to distinguish between different water-soluble substances. Like smell, taste is one of the chemical senses. For decades, it was considered an established fact that there are only four taste senses, namely bitter, salty, acid and sweet. On the other hand, despite numerous assumptions to the contrary, pungent is not a taste but a pain reaction. Similarly, the astringent effect in tannin-rich red wines, which should not be confused with bitter, is not a taste. Rather, it is a so-called tactile sensation (concerning the sense of touch) especially on the inside of the cheeks. The corresponding taste receptors in the form of papillae (wart-like nerve cells) are present on various zones of the tongue. From here, they are passed on to corresponding receptors in the brain and only perceived here. Corresponding receptors on the tongue and in the brain are thus considered proof of taste sensations. Taste was probably developed in the course of evolution because the taste of a food also allows conclusions to be drawn about its nutritional value. For example, sweetness stands for carbohydrate-rich foods that have a high nutritional value and provide many calories. The taste of salt or the hunger for salty food, on the other hand, helps people to keep their mineral balance in equilibrium.

In the 1990s, scientists defined umami as the fifth flavour, recognising glutamate (an amino acid). Umami was already officially recognised scientifically as the fifth flavour. In 2004, Purdue University in West Lafayette (Indiana) identified fat as the sixth flavour. Corresponding receptors for fat (mixed esters of glycerol and higher carboxylic acids with an even number of carbon atoms) are clearly present. A seventh receptor is suspected, but not yet scientifically proven, namely "water", which in its pure and unadulterated form superficially tastes "like nothing". But according to some scientists, the "nothing" is also a taste. The various scents, on the other hand, are perceived by receptors on two postage stamp-sized areas in the upper nasal cavity. However, when enjoying food and drink, as of course when enjoying wine, these impressions of the tongue and nose, which are first received in the brain, are mixed to form an overall impression, so that the definitive origin can no longer be traced. In combination with the taste sensations and in addition with the manifold scents, a complex variety of sensory nuances is created. However, the human nose is far superior to the tongue. Everyone knows the phenomenon that when you have a cold, you can recognise the taste directions, but the food "tastes like nothing" (better "smells").


The fifth taste - umami

Glutamate (full name monosodium glutamate) is the salt of glutamic acid and one of the many amino acids. The substance develops flavour-enhancing properties in food and plays a special role in the palatability and acceptability of many foods. In food seasonings such as Maggi or Knorr, the relevant proportion is monosodium glutamate, and this taste is also strongly felt in raw meat (for example, unseasoned beef tartar). Particularly high glutamate concentrations are found in ripe tomatoes, cheese, meat and human breast milk. The use of these properties has a long tradition in Far Eastern cuisine. That is why many people in Chinese restaurants, for example, like the "crispy ducks" so much, because the Chinese use glutamate very intensively in almost all dishes.

Asian cooks used extracts from large algae (species Laminaria japonica) to prepare their dishes as early as 1,500 years ago. As early as 1908, the Japanese scientist Kikunae Ikeda (1864-1936) discovered that glutamate gives many protein-rich dishes a full-bodied taste. He called this fifth flavour "umami" (engl. "deliciousness" or "pleasant taste"). Today, glutamate is used in numerous foods worldwide and, according to the WHO, has the ADI limit "not specified", i.e. can be ingested by humans without restriction. ADI stands for "acceptable daily intake".

In addition to the four taste directions bitter, salty, acid and sweet, acid, salty and bitter, umami has been identified as the fifth and has been scientifically recognised in the physiology of taste through various studies. Receptors responsible for the perception of glutamate were found in the cellular taste buds of the tongue. And just as with the other four, there are cells in the brain that explicitly receive and reproduce umami. Until then, it had been assumed that the sensation was merely a mixed taste of the other four. Since wine contains amino acids, umami could also be objectively recognised if present. The only problem is that, according to the above-mentioned studies, the receptors on the tongue are only extremely weakly developed compared to the reception sites in the brain (namely 1 in 100).


Smell

The sense of smell is the ability to perceive gaseous substances or substances dissolved in water on a molecular level. Like taste, smell is one of the chemical senses. The ability has only been proven in vertebrates and insects. In behavioural biology, smell has a special significance with regard to food intake, reproductive behaviour and recognition of enemies. For example, odours promote appetite and the formation of digestive juices. And the statement "that you can't smell someone" is much more than just a play on words. Scientific experiments have shown that when it comes to choosing a partner, smell is unconsciously very important. Likewise, smells play an important role in associative and memory brain processes. The threshold for perception is species-specific and scent-dependent. A dog, for example, has a million times stronger olfactory capacity than a human being.

Odours are perceived olfactorily (lat. "smelling") by two postage stamp-sized areas in the upper nasal cavity. Around ten million receptor cells pick up the scents and pass them on to the brain, where they are first perceived. A strong restriction arises in the case of a cold, where the six taste directions are recognised, but no smells. Since the source cannot be attributed to a large extent, olfactory impressions are very often falsely attributed to taste. This is because the human tongue is almost primitive compared to the nose. However, the human olfactory brain can perceive up to 4,000 different odours.

The taste zones of the human tongue

The problem is, however, that civilised people have forgotten how to identify smells. We no longer need this as we did in prehistoric times, when survival depended on it. The University of California developed the so-called aroma wheel, which can be used to identify the aromas of wine. During normal breathing, only a small part of the scents reach the receptors. Therefore, when evaluating a wine or addressing a wine, one has to "sniff" deeply in the glass with the nose. This must not be done too intensively, however, because otherwise the scents will pass the receptors of the nose and end up in the lungs.

The human tongue

The taste directions are perceived on very specific zones of the tongue (and to a very small extent on the inside of the cheeks). The corresponding nerve cells (papillae) are specialised in the respective taste direction and can only recognise this. Umami is perceived in the middle area of the tongue.

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