Tastebuds over time?

Tastebuds in the news! NPR ran a story yesterday that children’s love of sweet things might be based in their biology.  We all know that our tastes change over time, kids who refuse to eat anything green or spicy can grow up to love Thai green curry.  Our palates expand with time and exposure to new things. Kids are notorious for a dislike of bitter flavors, making an icky face after a sip of coffee or beer (that they begged to try!) But, new research shows that it’s not just exposure or cultural diet that causes our tastes to change as we age, children around the world show strong preferences for really sweet foods.

Researchers from the Monell Center in Philadelphia shows that humans are born with a much higher preference for sweet tastes, that fades when we approach adolescence.  This might be because sweet foods are high in easily digestible calories, that young children need for rapid growth.  NPR also cited research that shows that our desire for sweet foods decreases drastically in adolescence. When our bones finish growing, sweet preferences quickly decrease to adult levels.

Our sense of taste also changes with advanced age.  Although maybe not as obvious as deteriorating hearing or sight, we start losing taste buds in middle age.  Sweet and salty tastes frequently decrease in sensitivity more than sour or bitter tastes.  However, for many people, the effects are mimimal.

About 2 million people in the US have an impaired sense of smell. Permanent or temporary, this condition, called anosmia, can seriously affect people’s ability to enjoy foods. A friend of mine with anosmia occasionally catches certain smells, but misses many others.  She never notices when something is burning on the stove, or if someone just farted. However, she appreciates more complex flavors in food than just sour or salty.  Talking with her about it reminds you just how complex and connected our senses really are.

We might take our ability to taste or smell for granted, but people who have suddenly lost these senses often report a serious sense of disconnectedness with the world around them.  In Remembering Smell, Bonnie Blodgett describes losing her sense of smell and how it changed her perceptions of the world.  We use these senses subconsciously and constantly, so I look forward to reading more research on the roles these senses play in physiology, evolution, cognition, and culture.

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Taste Tests

I really like the taste of beer.  And so do many other people.  But “beer” obviously isn’t just one flavor, they vary in complexity from watery Natural Light to a complex craft-brewed Stout. There is such a variety of tastes that make up beers that the taste of beer can be hard to explain. Luckily, yesterday, at a beer tasting at the Wisconsin Science Festival, we learned how the sense we call “taste” really works.  We were each served a tray full of little labeled cups, full of mysterious liquids that definitely were not beer.

Jon Roll, a UW prof who teaches beer brewing courses, led the discussion. He explained that the tongue really only tastes 5 things, sweet, salty, sour, bitter, and umami. The rest of our sense of “taste” is actually the aromas of food, experienced by the nose.  The nose senses food aromas through two pathways. First, we inhale the scent of the food outside our mouths. We typically call this smell. However, when the aromas of food in our mouths reaches the nose through the nasal passageway, we refer to that as the taste of the food. Even though the olfactory nerves in the nose are responding the same we seem to mentally seperate these two processes.  We say that the roasting turkey smells good and then it tastes good too.  But when we say we are enjoying the taste, it is largely because of the smell.

We tasted sweet water. Then we tasted really sweet water. Blech. Then, going back for another sip of the first sample was striking, it tastes just like water.  Roll explained that the taste buds can get desensitized pretty easily to some flavors, so we stop registering them.  This is potentially a big concern for the manufactures of food, how to keep something tasting good all the way to the last sip without losing our sensitivity to the flavor?

Most of the receptors in the mouth for bitterness, we discovered, are near the back of the tongue and throat. Because of this, professional beer tasters always swallow the beer they are testing.  Unlike wine tasters, who can swirl it around in their mouths and then spit it out to describe the flavors, the bitterness component of beer is best sensed by swallowing. No one in the audience seemed upset to find out that we had to actually drink the beer.

To understand the role of our noses, Roll asked us to pinch our noses tight while rubbing a gum drop on our tongue.  It just tasted sweet. It wasn’t until you released your nose that the flavor of cinnamon became apparent. We looked silly, but we did it again. Same thing with spearmint. And orange.

However, your tongue does more that just taste the 5 famous flavors.  It also has physical responses to some flavors that can be called mouth-feel.  Taste something strongly sour, and your mouth puckers up and starts salivation.  Drink tea or red wine and the tannins can make your tongue feel strangely dry, even though you are drinking a liquid.

When we were finally served a sampler of beers, everyone was better equipped to describe what they tasted.  People sipped beer holding their noses, and then re-sipped with noses functional normally.  Complex beers like the porter we tried have a progression of flavors, from the early aromas of coffee or caramel, sweet in the middle, a pleasantly bitter finish.  In my opinion, it was the best one at the event. But, other people preferred the floral and bitter IPA.  To each their own tastes, apparently.

Dangerous exposure?

Yesterday when I came home, my roommate asked me to photograph her back.  It was covered in a grid of sticky patches and medical tape.  She’s being tested for skin allergies.  Some chemical in some of her clothing causes her to develop a rash, and she wants to find out what it is, so she can avoid it in the future.  Although, if she finds out that she’s allergic to, for example, a formaldehyde finishing resin, which are applied to clothing to create wrinkle resistance, how do you then go about buying clothes that are formaldehyde free?  It’s not like they list all of the chemicals on the tags of things we wear, like they do with shampoo or laundry detergent (other common causes of skin allergies).

What amazes me is how many little dots of irritants they are testing.  Who knew there could be that many potential allergens just in clothing? But then, when you think about just how many chemicals we are exposed to every day, I am surprised that her entire body isn’t covered in sticky dots.  Our lives are covered in synthetic chemicals, no matter how much organic food we buy.  We wear them, wash ourselves and things with them, and we breathe them in.

My mother refuses to go in a Bath and Body Works, and I agree with her. The overwhelming  smell of all of the different perfumed products is nauseating.  The powerful smell is a flood of chemical molecules rushing into your nose.  Luckily, most of us can just walk past to some fresher air, no worse for the wear. But for some people, inhaling even a trace amount of certain chemicals can cause serious symptoms. It’s called Multiple Chemical Sensitivity syndrome, and it’s a controversial diagnosis for a variety of symptoms that are very poorly understood.

The basic idea is that chemical exposure might affect a few people much more than it affects the general population. For those few people, the documented symptoms, ranging from headaches and nausea to breathing problems and physical weakness, can be debilitating. Identifying the chemical causes of such symptoms can be very difficult or impossible.  According to WebMD, many experts, including the American Medical Association think that the link between patients’ symptoms and chemical environmental factors are not well demonstrated. There is no clear medical test, understood cause and effect pathway, or specific treatment for MCS, but it persists as the best description for the symptoms people face.  A lot more research is needed before doctors and scientists will be able to describe it as a disease.

In the meantime, people living with extreme forms of MCS are taking drastic measures to live their lives without debilitating exposure.  In a photo-essay for NYT this weekend, Thilde Jensen, a MCS sufferer herself, shares photos of the drastic measures people have taken to live their lives.  People move to remote, rural areas, live completely outdoors, wear respirators, and limit their use of commercial products, from conventional building materials to clothing. In her essay, you can watch individuals use the solutions they have found to their specific symptoms.

It’s easy to imagine that the chemicals in our environment can cause all kinds of health problems. People with asthma struggle in smoggy cities. My dad once speculated that his lymphoma might have been the result of exposure to diesel fumes that leaked into the interior of the car he drove for many years. We know about major pollution events that have caused cancer clusters of people exposed to toxins. Since Rachel Carson sounded the alarm, we’ve been concerned about the chemicals we put out into the world, but it’s easy to forget the small, subtle chemical exposures we constantly face.  Very few people believe that they have MCS, but the rest of us breathe in the same things all of the time.  Scary thought, maybe we’re all experiencing effects that we have yet to detect, to varying degrees.  Does any one have or know any who has MCS like symptoms?

A new kind of Soda fountain…

Scientists love explosions.  They love using explosions, like the popular Mentos and Coke reaction, to get people excited about science. Add Mentos candies to a bottle of Diet Coke, and it will erupt in a fountain of bubbles, spraying 5-10ft high.

After the fountain subsides, students brainstorm: how and why did this reaction happen? The simple answer is that the rough surface of the candies provides lots of little growth sites for bubbles. The truth, like many things in science, is a bit more nuanced. In June, 2008, a physics professor from Appalachian State College and her students published a paper demonstrating all the factors that effect the reaction. Tonya Coffey’s class tested a variety of hypotheses by repeating the reaction with different kinds of soda, different candies, and other substances that have similar characteristics to the Mentos, like the rough surface of rock salt or sand.

They tested the rough surface hypothesis by comparing Wintergreen Lifesavers to Mentos.  Both candies, the rock salt, and even dish soap, caused bubbling eruptions. Anything dropped into the soda can break the fragile bonds between water molecules, allowing carbon dioxide bubbles to grow. But not all of the eruptions were the same size.  Under a microscope, the surface of the Lifesavers appears 5 times as rough as either the mint or fruit Mentos, which are very similar.  However, the eruption with the Lifesaver is half the size of the average mint or fruit Mentos eruption.

The difference they discovered is that Mentos are very dense, and sink to the bottom of the soda bottle 33% faster than the Lifesavers. The bubbles created at the bottom now have to travel all the way back to the top of the bottle to escape. The bubbles create a chain reaction, each one creating more as they disrupt the cohesion of the water molecules. The bubbles that travel from the bottom create more pressure, causing a more powerful the eruption. Coffey compares the Lifesaver’s reaction to a volcano slowly oozing lots of lava, instead of spraying high into the sky like the Mentos.

The second factor Coffey’s team found that plays a role in the high spray of the Diet Coke and Mentos or Fruit Mentos is the fact that the Coke is diet.  The artificial sweetener, aspartame, weakens the bonds of the water molecules in the soda. This makes it easier and faster to for the Mentos to break those bonds and start building bubbles.  A bottle of regular Coke erupts too, just not quite as high.

Hello World!

Hi, I’m Kate. I’ve been a botanist, a professional hiker, and fan of outdoor science for awhile. I’m starting on my new big adventure now, reading, writing, and building my career as a science writer. I plan to use this blog as a way to play with my writing, share the awesome things I’ve been reading, create connections to other interesting science writers and ideas, and dip my toes into the rushing water of journalism in our media frenzied age.