Today’s Wonder of the Day was inspired by Rosie from IA. Rosie Wonders, “Why are pickles sour?” Thanks for WONDERing with us, Rosie!

What's black and white, black and white, black and white…and green? Give up? It's three zebras fighting over a pickle, of course!

We don't know for sure if zebras like pickles enough to fight over them, but we sure like them. They're one of our favorite green foods here in Wonderopolis. By themselves or on a juicy cheeseburger, you just can't beat pickles!

But what exactly is a pickle? Believe it or not, it's a cucumber that has been pickled.

Pickling — also called "brining" — is a way of preserving food by fermenting it in vinegar or a saltwater solution called "brine." The word “pickle" actually comes from the Dutch word pekel, which means "brine."

The acetic acid in vinegar or the lactic acid produced by brine gives the pickle its salty, sour taste. Brine also can contain a variety of spices to add flavor to pickles.

Common spices added to brine include garlic, horseradish, dill, and white mustard seeds. To make pickles more sour, you can add more salt to the brine.

Many foods can be pickled. Commonly pickled foods include cabbage (called "sauerkraut") and pigs' feet.

What we all know as a pickle, though, is a pickled cucumber. People in England commonly call pickles "gherkins" because they often pickle a cucumber-like vegetable called a gherkin.

Not all pickles are sour. Bread-and-butter pickles, for example, have a distinctly sweet taste because sugar and other sweeteners are added to the brine.

Like tomatoes, cucumbers (and thus, pickles) are technically fruits. You won't likely find pickles — even sweet bread-and-butter pickles — in a fruit salad anytime soon, though.

Most people treat them like vegetables since they are grown like vegetables and aren't naturally sweet. As a snack, pickles offer a good fat-free, low-calorie alternative to high-fat, high-calorie snacks.

Since they're pickled in brine, though, you do need to be aware that pickles tend to have a higher level of sodium (salt) than other snacks. Pickles are also a source of vitamin K.

Wonder What's Next?

Tomorrow’s Wonder of the Day investigates how a few letters can say a lot!