Posted by Eric Troy on 17 Jun 2015 15:36
Bitter is one of the tastes that you can distinguish by the taste buds on your tongue, along with sweet, sour, salty, and unami. It was once though that you could only taste bitter with the back of your tongue, but we now know that bitterness can be registered by all parts of the tongue where taste buds reside. However, there are more bitter taste receptors on the back and sides of the tongue.
Bitter is a taste that we associate with toxic substances. Therefore, a strong bitter taste may also cause a gag reflex, which occurs as a protective mechanism. Bitter tastes stimulate the brain through the gloosopharyngeal nerve, which is also associated with the gag reflex.
Foods that are more alkaline, with a higher pH, have a more bitter flavor to us. Plants contain alkaloid components, many of which can be highly poisonous. These alkaloids have nitrogenous bases and are often present as salts of acetic, oxalic, lactic, malic, tartaric, citric, or other acids. Alkaloids can have very strong physiological effects in human beings. A well-known poisonous alkaloid is stryhnine. Others, however, such as caffeine are stimulants, or even, like morphine, analgesic. They can be quite beneficial, at times.
As well, metallic compounds, glycosides, and peptides are experienced as a bitter principle. The number of molecules that we perceive as bitter is very high, and these molecules show a wide variance in structure. The amino acids histidine, methionine, valine, arginine, phenylalanine, tryptophan, leucine, and tyrosine have a bitter taste. Lysine and proline are both sweet and bitter.
Since many sour foods are also bitter, bitterness is often confused with sourness. Many common cooking tips meant to remove bitterness from foods or recipes are actually countering sourness, and vice versa. The best way to counter bitterness is with sugar, which helps balance out bitter flavor.
Although bitterness is disliked when the taste is too strong, or when not expected in a food, it is often thought to be an important part of the overall flavor profile of certain products. This is true in chocolate, for example. A bitter component is considered an integral part of many beverages such as beer, wine, tonic water, tea, and coffee. Bitterness is such an important part of many cocktails that a special kind of mixer called "bitters" has long been used, the most famous of which is Angostura.
Bitter tastes are often accompanied by a type of mouth-feel called astringency, which is felt on the tongue and the mouth itself. This is also sometimes referred to as tannin since tannins tend to cause this feeling. This is the sensation of "mouth puckering" or having your tongue dried out and made to feel "rough" that comes from eating a bitter food or drinking a bitter beverage. Although we often describe it as if it were a taste, it is actually a sensation. Cranberries are bitter and astringent (and also sour), and are one of the best ways to experience this feeling. Astringency is associated with bitterness often enough that many people mistake it for bitterness itself.
Astringency is important in both tea and wine. It is thought that similar compounds are responsible for the astringency in both, collectively referred to as tannins, hence the designation given above. Among wine, it is more prevalent in reds, where the astringent components come principally from the grape skins and seeds. Some compounds, such as anthocyanins, may enhance astringency without actually contributing to bitterness on their own. In wines, this feeling of astringency which coats the mouth is sometimes described as "slippery." You may have seen the word "brisk" or "briskness" used by tea companies to describe their tea. This term refers to astringency. Both lemon juice and milk added to tea help counter this astringency.
You Either Love or Hate Bitter Tastes?
Since some people will passionately embrace a certain bitter food, and others will absolutely reject it, not matter how it is prepared, many people think that some people simply love bitter flavors and other people hate them. This is not true. One person may appreciate the bitterness in a certain food or beverage and then despise the overly bitter taste of another. For example, a person who seeks out bitter chocolate may still refuse to eat Brussels sprouts because they are too bitter. This probably has to do with the complexity of how bitter compounds are tasted. There are likely many mechanisms for perceiving bitterness. There may be multiple sites for bitter reception on the tongue, and how hydrophobic a certain compound is may affect the level of perception. Also, other components also present with bitter compounds may enhance the bitter taste. It could be possible, then, for a person to be a "super-taster" of the bitterness in one food, while finding it tolerable or even pleasant in another. In other words, Brussels sprouts may taste more bitter to one person than to another.
Brussel Spouts, Love them or Hate Them?
With this complexity comes a surprising twist. I mentioned Brussels sprouts. Some people, like myself, detest them and others enjoy them. This may reveal a genetic component to bitter tasting.
There are certain bitter compounds that not everyone has the ability to taste. Therefore, it is possible for some foods to taste exceedingly bitter to certain folks and not all that bitter at all to others.
The first discovery of this phenomenon occurred in 1931 with a chemical called phenylthiocarbamide (PTC). Chemist Arthur Fox, working for DuPont, was working with this chemical when he spilled some of it. A researcher working near him complained that it tasted bitter, but Fox himself didn't taste a thing. So, he conducted some informal experiments with friends and family and found that the compound tasted bitter to some but not to others. It was later found that a dominant genetic trait was responsible for the ability to taste PTC.
The association was so strong that the ability to taste PTC was used to prove or disprove paternity before DNA testing was available. Another similar compound is propylthiouracil (PROP).
Cruciferous vegetables like Brussels sprouts, broccoli, and kale contain compounds called glucosinolates. These compounds contain thiocyanate groups with nitrogen, carbon, and sulfur bonded in a series. These same groups are present in PTC and PROP and are thought to be responsible for the bitter taste. Therefore, the same genetic component that makes people detect large levels of these bitter compounds in PTC and PROP may be at work in Brussels sprouts haters. Chances are, if you can taste the bitterness of PROP, you will also be turned off by the bitterness of Brussels sprouts and perhaps other cruciferous vegetables. However, the mere ability to taste bitterness doesn't mean you'll hate a food! As above, our perception of bitterness and whether or not we like a certain food can have complex origins, including whether or not we have acquired a taste from a young age.
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