McDonald's (NYSE:MCD) has not changed the recipe of the Big Mac since the sandwich first hit menus in 1967.

In recent months, the chain has added a larger version (the Grand Mac) and a smaller one (the Mac Jr.), but aside from the size change, the sandwich has remained the same for nearly 50 years. It's a recipe so iconic that it has its own song popularized in a 1974 ad campaign -- "Two all-beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun."

Now, for the first time in its history, McDonald's is testing a new version of the Big Mac, though it's not dropping the classic version. .

McDonald's tested Sriracha this summer, and now it's bringing it to the Big Mac (not pictured). Image source: McDonald's.

What is McDonald's doing?

The fast-food chain has begun testing Sriracha Big Mac at locations in Columbus, Ohio, according to Nation's Restaurant News (NRN). The new sandwich features the traditional "special sauce" spiked with spicy Sriracha, a sauce the company has offered as an option on its burgers in select markets since June. The new Big Mac will be tested at 128 locations in Central Ohio through the end of the year, according to NRN, which noted that these are the same locations that tested the different size Big Macs earlier in 2016.

"Offering the addition of Sriracha to our Big Mac Special Sauce was a fun way for our culinary innovations team to think outside the box and continue to answer the call of our customers who are always looking for the next great innovation in food experience and taste," Scott Nickell, Central Ohio Co-op president, said in a statement reported by NRN.

The chain will decide after the test whether to roll out the sandwich nationwide. It is not uncommon for McDonald's to test a product that never makes it to the national menu.

In addition to the new Big Mac, the Ohio McDonald's involved in the test will also offer the Sriracha Big Mac sauce as a dipping sauce for Chicken McNuggets and french fries. That option was tried earlier this year in some West Coast locations.

Why is McDonald's doing this?

Everyone knows what a Big Mac is and most people know what Sriracha tastes like. Adding a variant of the classic sandwich featuring the popular sauce creates a new product that consumers immediately understand, which could entice lapsed customers to visit a McDonald's to try the new sandwich. It's important to not dilute a key brand like Big Mac, but the fast-food company has been very protective of its signature sandwich, making any change (or in this case new variety) count as an event. If people like the Sriracha Big Mac, then McDonald's will have a new menu item it can roll out nationwide that should create some excitement.

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