Perspectives

  • Issue 117 / May - June 2017



    Sweet, Sour, Salty, Bitter, and Umami

    Osman Senkaya

    We are taught that there are four basic tastes. But what taste best describes chicken soup, mushrooms, or pastrami? An NPR story recently explored how the line between specific tastes is actually quite blurry – and how some tastes don’t fit neatly into any of the four classic definitions:


    Auguste Escoffier was not just a chef; in Paris in the late 1800s he was the chef. He had opened the most glamorous, most expensive, most revolutionary restaurant in the city. He had written a cookbook, The Guide Culinaire. And, he also created meals that tasted like no combination of salty, sour, sweet, and bitter; they tasted new. He offered a spectacular new sauce that seemed to deepen and enrich the flavor of everything it touched.


    But because it was neither sweet, bitter, sour, salty nor any combination of those four, as far as scientists were concerned, it wasn't real. People may smack their lips, drool, savor, and pay enormous amounts of money to M. Escoffier, but what they tasted wasn't really there. It was all in their heads.


    Meanwhile, halfway across the world, a chemist named Kikunae Ikeda was at the very same time enjoying a bowl of dashi, a classic Japanese soup made from seaweed. He too sensed that he tasted something beyond categor[ization]. And it was, thought Ikeda, simply delicious.


    But what was it? Being a chemist, Ikeda could find out. He knew what he tasted was, as he wrote, "common to asparagus, tomatoes, cheese and meat but… not one of the four well-known tastes." Ikeda went into his lab and found the secret ingredient in 1908. He wrote in a journal for the Chemical Society of Tokyo that it was glutamic acid, but he decided to rename it. He called it umami (pronounced "oo-MA-mee"), which means "delicious" or "yummy" in Japanese. Ikeda then crystallized monosodium glutamate (MSG), the chemical ingredient responsible for umami, as a seasoning that would become popular worldwide, and began commercial distribution of MSG products. [1]


    Almost 100 years after Escoffier wrote his cookbook and Ikeda wrote his article, a new generation of scientists took a closer look at the human tongue and discovered, just as those two had insisted, there is a fifth taste. When something is really, really yummy in a non-sweet, sour, bitter, or salty way, that's L-glutamate you taste. This new taste was named "umami," in Ikeda's honor. [1]


    Umami is a Japanese word that means "good flavor" or "good taste." The closest English equivalent, taste-wise, is probably brothy or meaty. Umami describes the flavor common to savory products such as meat, cheese, and mushrooms. Bouillon cubes are the closest Western product that could be identified as umami. Unlike the other four tastes, umami is much vaguer and harder to pinpoint. All candies exhibit some sweetness, yet not all cheeses or vegetables will be umami. Although North Americans cannot easily identify this flavor, it's quite easily recognized in many East Asian countries because the idea of umami is a part of the culture. Thai fish sauce, for instance, is pure umami.


    Salts of umami, the most common of which is monosodium glutamate (MSG), are used as natural flavor enhancers which bring depth and balance to food without drowning out more subtle tastes. Valued at USD 4.5 billion, the global MSG market stood around 3,000 kilo tons in 2014. It appears in almost everything from fast food sausages to supermarket items like rapid-cooking soups, chips, bouillon cubes, ketchup, steak sauce, cheese, etc., providing flavor enhancement. What MSG has going for it is that it is a readily available, inexpensive, intensely umami ingredient with no off-flavors -- just as sugar is a classic expression of sweet and salt is perfectly salty.


    In many parts of Asia, it is as common to add a dash of MSG to dishes as it is for cooks here to toss in a little salt or sugar. But in the U.S., MSG has developed a bad reputation as a suspicious additive that many consumers believe causes allergies or headaches. [2] Concerns have been raised on anecdotal grounds. Hypotheses have been put forward that MSG may be associated with migraine headaches, food allergies, obesity, asthma, and hyperactivity in children, etc. Yet, subsequent research failed to present any causal association that MSG is responsible for these symptoms, even in studies with people convinced that they are sensitive to it. U.S. Food and Drug Administration "considers the addition of MSG to foods to be generally recognized as safe." [4]


    Umami in food
    In the wake of breakthroughs in food science, umami is going mainstream. Chefs are offering dishes that pile on ingredients naturally rich in umami to reduce the fat and salt content of foods without sacrificing flavor. Just as a few shakes of salt can improve a dish, a correctly applied dash of cheese or ketchup can pump up the umami without overwhelming the dish. [2] Packaged-food companies are trying to ramp up the umami taste in foods like low-sodium soup to make them taste better. Companies that develop flavorings for the food industry are seeking ways of delivering the taste to foods while also cutting back on fat, salt, sugar, and artificial ingredients. These can range from natural ingredients to artificial flavors that are to MSG what saccharine and aspartame are to sugar. [2]


    Umami blends well with other tastes to expand and ignite their flavors, and to awaken the taste buds. It is a subtle taste that occurs naturally in many vegetables and dairy products as well as in meat, fish, seafood, and their fermented or cured derivatives. However, it’s not as easily recognizable in the Western diet as sweet, salty, bitter, and sour. In Asian cuisines, umami is mainly found in beans and grain, fermented seafood-based products, shiitake mushrooms, soy sauce, fish sauce, Kombu, and dried seafood. These are all inherently rich in umami, without additives or chemicals. The most common example in Western cuisine is tomatoes. [3]


    Tomatoes are an indispensable ingredient that form the basis of a wide variety of dishes. The glutamate levels in tomatoes increase significantly in condiment forms such as juice, ketchup, paste, or sauce. Today, tomatoes are one of the most widely produced vegetables and their umami taste, especially present in ripe, juicy beefsteak tomatoes, is appreciated all over the world. [3]


    Foods high in protein are the best for sensing umami. Glutamate is released when protein is broken down through drying, aging, curing, smoking, slow-barbequing, or slow cooking; for instance, mushrooms better contribute to umami when sautéed, and meat that has been marinated is tastier. Many kinds of meat become tenderer when matured: the enzymes contained within the meat break down its proteins to increase the levels of umami-imparting amino acids. Processed beef products have higher levels of glutamate than meats do in their natural state. [3]


    Already rich in glutamates, milk further releases glutamic acid when it is cultured and aged to produce cheese. That’s why aged cheeses, such as cheddar and parmesan, are grated over or stirred into other dishes as seasonings or used as toppings to add a savory flavor. Parmesan cheese, also high in protein, is one of the world's most popular hard cheeses. More than two years are required for the maturation of parmesan. The glutamate content is so high that even a rind tossed into a soup pot deepens flavor. A large chunk of parmesan cheese will have small but visible white glutamate crystals, which were formed during maturation. [3]


    The sweetness and umami of green tea is provided by amino acids. Teas – such as green, black, and oolong – all originate from the leaf of the same tea plant, but variations in the production and processing result in differing beverages. Most of the tea consumed in China and Japan is unroasted green tea, where the essential elements of the tea plant are left largely intact. [3]


    Another food combining umami substances is the cheeseburger. Its combination of beef, cheese, and ketchup creates a delicious synergistic effect. The effect further increases when it is accompanied by fried potato, as potato slices lose water content when they are fried up, which concentrates the glutamic acid in each bite.3 Piles of umami toppings on pizza – tomatoes, pepperoni, mozzarella, and mushrooms – could explain why people love its savory taste and the full, tongue-coating sensation it provides.



















    Another role glutamates play



    Glutamates are important neurotransmitters in the human brain and play a key element in learning and memory. A sweet taste signals a source of energy, through sugars and carbohydrates. A salty taste signals the presence minerals that are essential to keeping the mineral balance of the body’s fluids. Sour tastes signal that something has gone bad in the food, and a bitter taste, meanwhile, signals that something is harmful to the body, such as a toxin. 



    On the other hand, umami is the taste of amino acids or nucleotides, and plays the role of signaling the presence of proteins, which are essential to human beings. Just as sweets serve as an incentive for carbohydrates, glutamate helps us enjoy proteins.



    Our body recognizes the various tastes via taste receptors on the surface of the tongue. Negating the opinion that each taste has its particular zone, research has revealed that all tastes can be detected anywhere around the tongue, as each taste bud has 50 to 100 receptors for each taste. Furthermore, separate taste receptors on the tongue with no purpose other than detecting umami have been discovered.



    What is more, recent research has discovered that there are glutamate receptors not only on the tongue but also in the stomach. It has been ascertained that the pneumogastric vagus nerve only reacts to glutamate. This suggests that when a piece of food enters the stomach, and glutamate receptors detect the presence of glutamate, this information is relayed to the brain by the vagus nerve and an order is sent from the brain to the stomach to prepare for digestion. 



    As we see here, the whole system – of taste, sense, and digestion – is tied together. One can only marvel at the incredible design of such a complex system - maybe while enjoying a delicious, umami cheeseburger!



    Notes



    [1] Krulwich, Robert. "Sweet, Sour, Salty, Bitter… and Umami." NPR. http://www.npr.org/templates/story/story.php?storyId=15819485.



    [2] McLaughlin, Katy. "A New Taste Sensation." The Wall Street Journal. http://online.wsj.com/article/SB119706514515417586.html.



    [3] Umami Information Center. http://www.umamiinfo.com/.



    [4] https://www.fda.gov/food/ingredientspackaginglabeling/foodadditivesingredients/ucm328728.htm


    Figure 1. Examples of umami food















































































    Food



    Naturally occurring glutamate (mg/100g)



    Green
    tea



    220
    - 670



    Anchovies



    630



    Oyster



    40
    - 150



    Cheddar
    cheese



    180



    Parmesan
    cheese



    1200
    - 1680



    Soy
    beans



    70
    - 80



    Soy
    sauce



    400
    - 1700



    Tomatoes



    150
    - 250



    Dried
    tomatoes



    650
    - 1140



    Shiitake
    mushroom



    70



    Dried
    shiitake mushroom



    1060



    Garlic



    100



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