All about popcorn

Did you know that popcorn is made from a special kind of corn? I had never really thought about it before, but if asked, I would have guessed that you could use any old corn to make popcorn. All you have to do is dry some kernels, then heat them up and they'll pop, correct?

Actually, no, it turns out that popcorn is a little more sophisticated than that. In researching how it's more sophisticated, I've learned some things about corn that I never knew before.

All corn is a type of maize, of which there are 6 kinds - pod, sweet, flour, dent, flint and pop. The kernels of all kinds of corn are made of 3 things - the germ, the endosperm and the pericarp. The germ is the only living part of the kernel. It's right in the middle of the kernel, and contains the information necessary for that kernel to produce a whole new corn plant (genetic material, enzymes, vitamins and minerals). It's also the part of the kernel that produces corn oil - about 25% of the germ consists of corn oil. The endosperm is the largest part of the kernel. It accounts for over 80% of the kernel's dry weight, and consists largely of starch. The endosperm lies between the germ and the pericarp, or outer hull. The pericarp is very tough, and is designed to prevent moisture loss from the inside of the kernel, as well as protecting the delicate germ from being eaten by bugs or microbes.

Different kinds of corn differ in how much of these 3 components the kernels have, as well as their starch and oil composition. Dent corn, for example (the leading type of corn grown on US farms), has an endosperm consisting of horny starch on the sides and soft starch on the top. As the kernels age, the soft starch shrinks, making a characteristic "dent" in the top of the kernel. Flint corn has no soft starch at the top of the endosperm, so it does not make a dent as it matures. The endosperm of flour corn consists mainly of soft starch, which makes it very easy to grind into flour. Sweet corn, grown for human consumption, has much less starch than any other kind. That's because the sugar in the kernels is not converted into starch in the endosperm - hence the sweet nature of the food. Pod corn is a very pretty kind of corn, with kernels that often turn a variety of colors. It is not eaten very often, but instead is grown to use for decorative purposes. And then, of course, there is popcorn.



Popcorn is specifically - and scientifically - known as Zea mays everta. It is a derivative of flint corn, and is distinctive in that it has a very thick pericarp. The thickness of its pericarp allows for the popping process to occur. When the water inside the germ is heated, it turns into steam. The thick pericarp holds the steam in, where it begins to gelatinize the internal starch and protein in the endosperm. Once the pressure of the steam gets too great, the pericarp bursts, releasing the starch protein and steam in a big pop. As the starch expands, it cools and solidifies into its distinctive popcorn shape.

There are several variables that go into how well popcorn will pop. One important factor is how quickly the popcorn is heated. The internal temperature has to reach about 180 degrees celsius (356 degrees fahernheit) before it will burst. If the kernel is heated too quickly, the external portion of the endosperm will release steam too quickly, bursting the pericarp before the internal part cooks properly. If it is heated too slowly, the building steam may leak out of the tip of the kernel, and it won't pop at all. Popping quality also depends on how much moisture the kernel contains. If there is a lot of moisture in the kernel, it will pop into chewy, soggy pieces of popcorn. Also, very moist kernels of popcorn tend to go moldy easily. If the kernel is too dry, however, it will not produce enough steam to pop well. So popcorn growers usually carefully control the moisture level of their popcorn kernels, and try to dry them out to around 15% of the total kernel weight being moisture.

There are lots of other interesting facts about popcorn that I came across when writing this entry. Here are a few of my favorites:


1. Popcorn usually pops in one of 2 shapes - mushroom (on the left) or snowflake (on the right). Different kinds of popcorn can produce exclusively one shape or the other, or a mix of the 2. Snowflake popcorn is usually used for eating straight as popcorn, which mushroom popcorn is usually used for popcorn confections (like caramel corn).

2. Popcorn kernels can move a distance of up to 3 feet when they burst.


3. "Popability" refers to how many kernels of a given batch of popcorn will pop. Some kernels simply do not pop, and are known in the popcorn industry as "old maids." They are assumed to either by too dry to produce enough steam, or have too leaky a pericarp.


4. Popcorn is the official state snack food of Illinois - which, by the way, produces a lot of the US supply of popcorn.


5. Scientists have found popcorn kernels over 1000 years old in tombs in both Peru and southwestern Utah.



Personally, I really enjoy eating popcorn. And I'm not alone. Apparently, Americans consume an average of somewhere around 17 billion quarts of the stuff per year. That's a lot of popcorn!

Sitting in the catbird seat

I was in the car this morning, and one of my favorite programs on NPR came on the radio. It's a short little thing, usually just 2 or 3 minutes long, but it's always so interesting! The program is called "Bird Note," and every episode describes something about birds. Wild or tame, big or small, common or rare, showy or drab - it runs the gamut. The narrator sometimes talks about the behaviour of the birds, or their environment, or their plumage. One particularly interesting one a few weeks ago compared how much effort it would be for a human to build a nest comparable to that made by a robin. (It would actually be really, really difficult!) Today's show was about a bird called a catbird. Actually, it was about an idiom in which the catbird features prominently - as you might have guessed from the title, the idiom is "sitting in the catbird seat."

I'd never heard this phrase before, but the narrator explained that this phrase means having an enviable position, the upper hand, or the greater advantage in a situation. And the reason it means this is perfectly explained by the behavior of the catbird.

Catbirds are American birds of the mimid family. "Mimid" is Latin for "mimic," and mimids are known for the vocalization abilities. Other mimids include thrashers, mockingbirds and tremblers. The catbird's standard call sounds roughly like a yowling cat, actually, though it can also imitate other birds. (It's alarm or warning call sounds startlingly similar to a male mallard.) There are two kinds of North American catbirds. The grey catbird is the most common, and is found across the US in all kinds of environments (rural, suburban and urban). They are medium-sized and dark in color, with the only notable coloration being a rust-colored patch under their tails. The other kind of catbird is the black catbird, which is found more in Central America and Mexico.

So what does the catbird do to deserve having an entire idiom phrased after it? The catbird (like many animals) relies on height to assert superiority or dominance. If a catbird feels threatened, it will go to the highest position it can find to call out its warning call. The higher that position, the more likely the intruder will back off. In addition, if two male catbirds are jockeying to be the top male in the area (and thus attract the best female), they will take gradually higher and higher perches, trying to outsing the other, until one is at the highest point. The bird who gets the highest is the winner. And, of course, the high perch from which he claims his victory is called "the catbird seat."

So there you go. Sitting in the catbird seat means getting the most advantageous position.

I love finding examples of how something science-related has worked its way into everyday life and language. Okay, so maybe this phrase isn't the most common, everyday phrase you'll ever hear. But now, if you ever do hear it again, not only will you know what it means, you'll also know where it comes from!

Anyone have any other suggestions for phrases or idioms that have their origins in science?

The science of fireworks

In recognition of the fact that tomorrow is the 4th of July, I'd like to spend today's post talking about fireworks. I love watching fireworks - the colors, the shapes, the sizes, and the different ways they twirl and burst and shimmer and sparkle are all entrancing to me. In thinking about fireworks, I wanted to investigate and see if what I think I know about fireworks is really true. In particular, I wanted to look into the science behind what makes fireworks different colors. I believe that I already know a little bit of the answer (as may you), but since it never hurts to have our knowledge expanded upon, here we go...

First, let's talk about the kind of firework that we are most familiar with in fireworks displays during the 4th of July - skyrockets. Skyrockets are projected into the air before they explode (unlike ground fireworks such as catherine wheels, which are like small, glowing ferris wheels that spin as they burn). These are built around a basic design - paper or pasteboard tubing filled with a combustible material, called pyrotechnic stars. Different tubes filled with different pyrotechnic stars can be combined in various ways to make the many shapes, sizes and colors that are seen when the firework explodes.

Pyrotechnic stars contain 5 basic components. First, there must be a combustible fuel to burn. Second, there is an oxidizer. This provides the oxygen required to start the burning process in the first place. (For a reminder about oxidizers, you can read my entry on flaming gummy bears.) Third, there is also something to hold the entire firework together, called the binder. And finally, there are chemicals which burn to provide the color, as well as another chemical to help strengthen the color of the flame produced.

So I was right - the color is provided by the burning of certain chemicals. Here's something I didn't know - a few of the chemicals that are used in producing fireworks displays:
Red: strontium or lithium salts
Orange: calcium chloride or calcium sulfate
Yellow: sodium salts such as sodium nitrate or cryolite
White: magnesium, aluminum or barium oxide
Green: Barium chloride
Blue: Copper chloride
Silver: Titanium or magnesium

Apparently, the most difficult color to achieve is blue. That's because copper is a tricky metal to burn. If it does not reach a high enough temperature, it will not emit enough light to be seen. However, if it gets too hot, it will fall apart before it produces any light at all. So consider yourself lucky if you wee a blue firework! Actually, all of the color-producing chemicals have to be handled carefully to achieve the right color. If there is a small amount of chemical impurity, thee metal will not burn properly. In particular, trace amounts of sodium burn so well that they easily overpower the intended color, producing yellow-orange instead.

I think my favorite kind of firework is called the willow firework. What's a willow firework? Well, your basic firework is called a peony. It makes a spherical burst of colored stars. Building off that, your next most common firework is the chrysanthemum, which is like a peony but with longer burning stars which leave a visible trail behind them. The willow firework is a variation on a chrysanthemum, but it has extremely long burning silver or gold stars. These burn so long that a long trail of sparks can be seen falling gracefully to the ground, just like a weeping willow tree.

Unfortunately, this year we probably will not watch a display of fireworks ourselves, but we may get to watch one on TV. Of course, it's not quite the same as in person, but it's better than nothing!

Catnip - a really good kitty drug

I've said it before, and I'll say it again - science is everywhere, all around us, in so many different things that we see all the time. I am reminded of that quite frequently when I spend a few minutes looking at our cats. There are many things that our two kitties do that spark questions in my mind, and today is no exception. What I want to explore today is the following question - how does catnip work?

For those of you with cats, you are probably familiar with what catnip does to a cat. But for those of you who don't, let me describe a scene for you. We have a toy for our cats that is a catnip-stuffed mouse. Fairly standard, as far as housecat toys go, but this one is a cut above most catnip-stuffed mice in that it has a pouch inside of it that you can refill with new catnip. So as the cats play with the mouse, though the catnip (a) slowly loses potency and (b) slowly leaks out of the pouch, it doesn't matter, because we can put new, fresh catnip in. Now, right after we fill the mouse with new catnip, it's quite amusing to watch our cats play with it. They rub their faces all over it, they lick it over and over again (until it's drenched in cat spit), they bat it around and around and around, and then they run like maniacs chasing it. And, just so you know, this is the only toy that causes them to act like this. (This is not really normal behavior for them). It's the fresh catnip - they love it. Love, love, love, love, love it! And from what I understand, our cats are not alone in their catnip obsession. Many cats love catnip. About 70-80% of domestic cats have some sort of reaction to it. They love to smell it, roll in it, lick it, rub their faces in it, and it tends to make them go a little bit nutso. Honestly, it's like a kitty drug!

So I was watching this unfold the other day, and I wondered - why does catnip affect cats so strongly?

Catnip is an herb related to mint. It's native to Europe, Asia and Africa, but has long since been established in the Americas, too. It's not entirely clear why it has such a potent affect on most cats, but here's what I've been able to find out. Catnip leaves contain a volatile oil (volatile means that it vaporizes easily) called nepetalactone. The nasal passages of cats is sensitive to this oil; when cats smell the oil, it stimulates sensory neurons that transmit messges to several parts of the cat's brain. In particular, it stimulates the amygdala (which controls emotional response to stimuli) and the hypothalamus (which regulates lots of different activities including emotions). The stimulation of these two areas of the brain cause the intense emotional reaction to the herb.

There are a few things that should be noted about catnip. First, cats will become desensitized to it after a few minutes. This seems to be analogous to how our noses become desensitized to a particular odor if we'rearound it long enough. A cat will only respond to catnip for a short while, then it ceases to have an effect. However, if they walk away from it for a while, then come back, their noses will be sensitive to it again. Second, it is not addictive. Cats do not become dependent on it, no matter how much of it they have. Third, it apparently has no effect in humans. This is presumably because our noses do not have the receptor for the nepetalactone oil. And finally, even large cats like tigers and lions appear to be susceptible to it.

I think it would be fairly amusing to watch a big, ferocious tiger rolling around, rubbing his face in a catnip bush! It would strike me as fairly undignified, for what is otherwise a thoroughly dignified animal.