Ever get the urge to drink a glass of tomato juice on a flight? You aren't alone, and there's a scientific explanation why.

Every day, about eight million people travel by plane. Up in the stratosphere, hurtling along in a metal tube, those people will do some pretty strange things. Like spend 10 bucks on a can of Budweiser, watch back-to-back episodes of "The Golden Girls," or buy something... anything... from SkyMall.

But few high-altitude behaviors are as strange as our sudden thirst for tomato juice. The thick savory drink isn't so popular at sea level, but for many airplane passengers, it's their first choice.

Guillaume De Syon is a professor at Albright College and an aviation historian. He says tomato juice on planes is a long-standing tradition, and it all started in the early days of commercial air travel. Back then, flying could be pretty terrifying.

"The flights were very noisy, there was a lot of vibration, you could hear the engine much more than you do nowadays, so drinking actually was a nice way of calming the nerves," says De Syon.

"Once you got bored of course you would drink some more, and before in-flight entertainment, such as movies, this is what people did, to the extent that by the time they landed, say from a trans-Atlantic flight, it was not uncommon to see passengers completely drunk, trying to get through customs."

But as jets got bigger and passenger loads increased, airlines couldn't afford to serve free booze on every flight. Plus, charging for drinks was a great way to keep passengers from getting belligerent. When the industry was de-regulated in the late 70s, competition got stiff and airlines began charging for more of their services, including food and beverages. Free drinks started to fade away, but mixers — like tomato juice — stayed firmly on the menu.

But that doesn't explain why people drink so much of it today.

"It's actually a question airlines have been asking," says De Syon. "How is it that they have to carry tomato juice?"

A few years ago, the German airline Lufthansa realized they served about 53,000 gallons of tomato juice annually. That's just shy of the 59,000 gallons of beer they serve each year. Which is really significant, says Lufthansa catering executive Ernst Derenthal.

"I mean, Germans are known as a beer drinking nation, and that's one of our favorite things and we are proud about it."

Lufthansa wanted to know why passengers drank so much tomato juice, so they hired the Fraunhofer Society, a German research institute, to study it. Researchers put people in a flight simulator -- the fuselage of an old Airbus A310. It perfectly mimicked the environment at altitude, complete with cabin pressure, turbulence, engine noise – even pictures of a blue sky and clouds taped to the windows. Then they served the participants food and beverages and had them report on how it tasted.

People consistently rated tomato juice as tasting better in the fake airplane than in a normal environment.

"We learned that tomato juice being on ground level is rather -- I'm not saying moldy, but it tastes earthy, it tastes not overly fresh," says Derenthal. "However, as soon as you have it at 30,000 feet, tomato juice shows, let's say, its better side. It shows more acidity, it has some mineralic taste with it, and it's very refreshing."

Here's why: When you're cruising at altitude, cabin pressure is low -- similar to the atmosphere one mile above sea level. That low pressure does several things. Your blood gets less oxygen, which makes your odor and taste receptors less sensitive. Mucus in your nasal cavities also expands in the low pressure environment, which makes it even harder to taste.

On top of that, most airlines keep the cabin at about 10 to 15 percent humidity. This dries out your nose and mouth, cutting down your sense of taste even more. Congestion, dehydration -- it feels kind of like having a bad cold. Sweets are less sweet, salty food is less salty, and it's harder to taste certain herbs and spices (curry retains its flavor at altitude, but that's another story). As a result, most airplane food tastes bland, but tomato juice actually tastes better up in the air.

But Derenthal and his colleagues weren't satisfied. After all, most passengers don't know that tomato juice tastes any different at altitude, but they order it anyway. There must be something else going on.

"So we started observing passenger behavior, and then, of course, talking to flight attendants often," says Derenthal.

They soon realized that everyone has a different reason for drinking tomato juice. Some drink it because it's filling. Others say it settles the stomach and helps with air sickness. And most people just drink it because it's there.

"Many people, they have not made their mind up, and just wonder 'What should I drink? In two minutes I will be asked by the flight attendants,'" says Derenthal. "And then you see someone in front of you having a tomato juice and you think, 'Why not? That's a good idea. Oh, I'll have the same as the gentleman in the other row.'"

Most likely, it's a combination of all these things. A lot of biology, a little history, and a dash of the unknown (maybe some Tabasco in there, too).