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A plate of Chinese takeout with egg rolls and duck sauce
A plate of Chinese takeout with egg rolls and duck sauce
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What is Duck Sauce?

A plate of Chinese takeout with egg rolls and duck sauce
A plate of Chinese takeout with egg rolls and duck sauce
iStock

We know that our favorite Chinese takeout is not really authentically Chinese, but more of an Americanized series of menu options very loosely derived from overseas inspiration. (Chinese citizens probably wouldn’t recognize chop suey or orange-glazed chicken, and fortune cookies are of Japanese origin.) It would also be unusual for "real" Chinese meals to be accompanied by a generous amount of sauce packets.

Here in the U.S., these condiments are a staple of Chinese takeout. But one in particular—“duck sauce”—doesn’t really offer a lot of information about itself. What exactly is it that we’re pouring over our egg rolls?

Smithsonian.com conducted a sauce-related investigation and made an interesting discovery, particularly if you’re not prone to sampling Chinese takeout when traveling cross-country. On the East Coast, duck sauce is similar to sweet-and-sour sauce, only fruitier; in New England, it’s brown, chunky, and served on tables; and on the West Coast, it’s almost unheard of.

While the name can describe different sauces, associating it with duck probably stems from the fact that the popular Chinese dish Peking duck is typically served with a soybean-based sauce. When dishes began to be imported to the States, the Americanization of the food involved creating a sweeter alternative using apricots that was dubbed duck sauce. (In New England, using applesauce and molasses was more common.)

But why isn’t it easily found on the West Coast? Many sauce companies are based in New York and were in operation after Chinese food had already gained a foothold in California. Attempts to expand didn’t go well, and so Chinese food aficionados will experience slightly different tastes depending on their geography. But regardless of where they are, or whether they're using the condiment as a dipping sauce for their egg rolls or a dressing for their duck, diners can rest assured that no ducks were harmed in the making of their duck sauce.

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A plate of Chinese takeout with egg rolls and duck sauce
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Big Questions
What Causes Sinkholes?
Mark Ralston/AFP/Getty Images
Mark Ralston/AFP/Getty Images

This week, a sinkhole opened up on the White House lawn—likely the result of excess rainfall on the "legitimate swamp" surrounding the storied building, a geologist told The New York Times. While the event had some suggesting we call for Buffy's help, sinkholes are pretty common. In the past few days alone, cavernous maws in the earth have appeared in Maryland, North Carolina, Tennessee, and of course Florida, home to more sinkholes than any other state.

Sinkholes have gulped down suburban homes, cars, and entire fields in the past. How does the ground just open up like that?

Sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can't take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is so prone to sinkholes because it has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren't left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

About 10 percent of the world's landscape is composed of karst regions. Despite being common, sinkholes' unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

A version of this story originally ran in 2014.

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Big Questions
How Are Speed Limits Set?
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When driving down a road where speed limits are oppressively low, or high enough to let drivers get away with reckless behavior, it's easy to blame the government for getting it wrong. But you and your fellow drivers play a bigger a role in determining speed limits than you might think.

Before cities can come up with speed limit figures, they first need to look at how fast motorists drive down certain roads when there are no limitations. According to The Sacramento Bee, officials conduct speed surveys on two types of roads: arterial roads (typically four-lane highways) and collector streets (two-lane roads connecting residential areas to arterials). Once the data has been collected, they toss out the fastest 15 percent of drivers. The thinking is that this group is probably going faster than what's safe and isn't representative of the average driver. The sweet spot, according to the state, is the 85th percentile: Drivers in this group are thought to occupy the Goldilocks zone of safety and efficiency.

Officials use whatever speed falls in the 85th percentile to set limits for that street, but they do have some wiggle room. If the average speed is 33 mph, for example, they’d normally round up to 35 or down to 30 to reach the nearest 5-mph increment. Whether they decide to make the number higher or lower depends on other information they know about that area. If there’s a risky turn, they might decide to round down and keep drivers on the slow side.

A road’s crash rate also comes into play: If the number of collisions per million miles traveled for that stretch of road is higher than average, officials might lower the speed limit regardless of the 85th percentile rule. Roads that have a history of accidents might also warrant a special signal or sign to reinforce the new speed limit.

For other types of roads, setting speed limits is more of a cut-and-dry process. Streets that run through school zones, business districts, and residential areas are all assigned standard speed limits that are much lower than what drivers might hit if given free rein.

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

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