Why Does Asparagus Make Your Pee Smell Funny?


The asparagus has a long and storied history. It was mentioned in the myths and the scholarly writings of ancient Greece, and its cultivation was the subject of a detailed lesson in Cato the Elder's treatise, On Agriculture. But it wasn't until the turn of the 18th century that discussion of the link between asparagus and odorous urine emerged. In 1731, John Arbuthnot, physician to Queen Anne, noted in a book about food that asparagus "affects the urine with a foetid smell ... and therefore have been suspected by some physicians as not friendly to the kidneys." Benjamin Franklin also noticed that eating asparagus "shall give our urine a disagreeable odor."

Since then, there has been debate over what is responsible for the stinky pee phenomenon. Polish chemist and doctor Marceli Nencki identified a compound called methanethiol as the cause in 1891, after a study that involved four men eating about three and a half pounds of asparagus apiece. In 1975, Robert H. White, a chemist at the University of California at San Diego, used gas chromatography to pin down several compounds known as S-methyl thioesters as the culprits. Other researchers have blamed various "sulfur-containing compounds" and, simply, "metabolites."

More recently, a study demonstrated that asparagusic acid taken orally by subjects known to produce stinky asparagus pee produced odorous urine, which contained the same volatile compounds found in their asparagus-induced odorous urine. Other subjects, who normally didn't experience asparagus-induced odorous urine, likewise were spared stinky pee after taking asparagusic acid.

The researchers concluded that asparagusic acid and its derivatives are the precursors of urinary odor (compared, in different scientific papers, to the smell of "rotten cabbage," "boiling cabbage" and "vegetable soup"). The various compounds that contribute to the distinct smell—and were sometimes blamed as the sole cause in the past—are metabolized from asparagusic acid.

Exactly how these compounds are produced as we digest asparagus remains unclear, so let's turn to an equally compelling, but more answerable question:


Remember when I said that some people don't produce stinky asparagus pee? Several studies have shown that only some of us experience stinky pee (ranging from 20 to 40 percent of the subjects taking part in the study, depending on which paper you read), while the majority have never had the pleasure.

For a while, the world was divided into those whose pee stank after eating asparagus and those whose didn't. Then in 1980, a study complicated matters: Subjects whose pee stank sniffed the urine of subjects whose pee didn't. Guess what? The pee stank. It turns out we're not only divided by the ability to produce odorous asparagus pee, but the ability to smell it.

An anosmia—an inability to perceive a smell—keeps certain people from smelling the compounds that make up even the most offensive asparagus pee, and like the stinky pee non-producers, they're in the majority.

Producing and perceiving asparagus pee don't go hand-in-hand, either. The 1980 study found that some people who don't produce stinky pee could detect the rotten cabbage smell in another person's urine. On the flip side, some stink producers aren't able to pick up the scent in their own urine or the urine of others.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

Does Sound Travel Faster or Slower in Space?


Viktor T. Toth:

It is often said that sound doesn’t travel in space. And it is true … in empty space. Sound is pressure waves, that is, propagating changes in pressure. In the absence of pressure, there can be no pressure waves, so there is no sound.

But space is is not completely empty and not completely devoid of pressure. Hence, it carries sound. But not in a manner that would match our everyday experience.

For instance, if you were to put a speaker in interstellar space, its membrane may be moving back and forth, but it would be exceedingly rare for it to hit even a single atom or molecule. Hence, it would fail to transfer any noticeable sound energy to the thin interstellar medium. Even the somewhat denser interplanetary medium is too rarefied for sound to transfer efficiently from human scale objects; this is why astronauts cannot yell to each other during spacewalks. And just as it is impossible to transfer normal sound energy to this medium, it will also not transmit it efficiently, since its atoms and molecules are too far apart, and they just don’t bounce into each other that often. Any “normal” sound is attenuated to nothingness.

However, if you were to make your speaker a million times bigger, and let its membrane move a million times more slowly, it would be able to transfer sound energy more efficiently even to that thin medium. And that energy would propagate in the form of (tiny) changes in the (already very tiny) pressure of the interstellar medium, i.e., it would be sound.

So yes, sound can travel in the intergalactic, interstellar, interplanetary medium, and very, very low frequency sound (many octaves below anything you could possibly hear) plays an important role in the formation of structures (galaxies, solar systems). In fact, this is the mechanism through which a contracting cloud of gas can shed its excess kinetic energy and turn into something compact, such as a star.

How fast do such sounds travel, you ask? Why, there is no set speed. The general rule is that for a so-called perfect fluid (a medium that is characterized by its density and pressure, but has no viscosity or stresses) the square of the speed of sound is the ratio of the medium’s pressure to its energy density. The speed of sound, therefore, can be anything between 0 (for a pressureless medium, which does not carry sound) to the speed of light divided by the square root of three (for a very hot, so-called ultrarelativistic gas).

This post originally appeared on Quora. Click here to view.

What Is Bologna Made Of?


Like hot dogs and SPAM, bologna is often regarded as something of a mystery meat. Regardless of your feelings about this much-maligned cold cut, bologna is a familiar presence in supermarkets, school cafeterias, and maybe even your own fridge. But what exactly is it?

Similar to the a handful of other curious foods, the answer really depends on the deli or manufacturer. The meat can be made from cured beef, chicken, or pork—or some combination of the three. Some varieties are made from premium cuts of meat, while others are made from ground-up organs, trimmings, and other unmentionables. However, products containing the latter are usually labeled as having "byproducts" or "variety meats," and they're (thankfully) hard to find in grocery stores nowadays, according to The Takeout.

The meat is cooked and smoked, and sometimes wrapped in a casing that's made from the gastrointestinal tracts of cows, sheep, or hogs, according to The Journal Times. This is the norm for several varieties of sausage, and it sure beats synthetic casings, which can be made from collagen and sometimes plastic. However, the casings are often removed before the product is sold commercially.

Although it's now one of America's favorite sandwich fillings, the lunch staple was named after the city of Bologna in northern Italy—even though Italians would turn their noses up at the stuff we're sandwiching between two slices of white bread. (And don't forget the processed American cheese!)

Their version of bologna—known as mortadella—has different colored spots on its surface. That's because it contains bits of fat, peppercorns, and sometimes sliced pistachios. In the U.S., on the other hand, the USDA says all cooked sausages (including bologna and hot dogs) must be comminuted, or "reduced to minute particles." In other words, the ingredients are emulsified and churned into a homogenous pink meat paste. As The Huffington Post puts it, "Mortadella is to bologna as fresh, roasted turkey on Thanksgiving is to sliced turkey lunchmeat."

Oscar Mayer, one of the best-known bologna producers, sells one variety made from "mechanically separated" chicken and pork, with a little bit of beef added in. According to the USDA, "Mechanically separated meat is a paste-like and batter-like meat product produced by forcing bones, with attached edible meat, under high pressure through a sieve or similar device to separate the bone from the edible meat tissue."

Aside from the meat, the recipe contains a blend of spices. A few of the most common ones added to bologna include salt, pepper, celery seed, coriander, paprika, and sugar—or, more commonly, corn syrup. And myrtle berry is often the secret ingredient that gives the meat its signature taste.

Although many companies won't reveal their preferred blend of spices, most of the ingredients in bologna are no secret. They're listed on the package, free for all to read. As it turns out, most mass-produced varieties of bologna are a lot less gross than you may think—as long as you're ok with corn syrup-flavored meat batter. Who's hungry?

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.