Burger King is offering a brand-new twist to its signature Whopper that uses an all-vegetarian patty but still tastes like meat.

The fast-food giant partnered with start-up Impossible Foods to make the vegetarian burger available at 59 stores in St. Louis.

Impossible Burger

The Impossible burger is made of heme from the roots of the soybean plant. It is an iron-rich protein that is mass produced using yeast. Other vegetarian ingredients were combined to give the patty its nutty texture similar to ground beef.

"We took the DNA from soy plants and inserted it into a genetically engineered yeast," Impossible Foods said on its website.

Fernando Machado, Burger King's chief marketing officer, said more customers are looking to consume less meat especially beef. The Impossible burger has about the same amount of protein as the Whopper, 15 percent less fat, and 90 percent less cholesterol.

The Impossible burger will be prepared in the exact same way as the traditional whopper. The vegetarian patty will be wrapped in a sesame-seed bun to be served in a white wrapper with the Impossible label on it.

"We see there is no compromise on taste, and lots of upside on things that people seem to be looking for," Machado said.

In a social experiment, Burger King served plant-based burgers without the customers knowing it. Patrons said the Impossible burger tasted exactly like the traditional Whopper.

White Castle announced in December that it would permanently add the Impossible slider on its menu. American burger chain had a successful test run of Impossible's meatless burger in September last year.

Boon And Bane Of Health

Critics think that Impossible Foods' meatless burger is not necessarily a healthier alternative to a beef burger. Its main ingredient soy leghemoglobin is derived from genetically engineered yeast.

The U.S. FDA did not certify the safety of SLH. It has never been used as an ingredient in human food supply before. The agency is also concerned that SLH could be an allergen.

"Although proteins are a part of the human food supply, not all proteins are safe," FDA said in a legal document obtained through the Freedom of Information request by the ETC Group. "Information addressing the safe use of modified soy protein does not adequately address safe use of soybean leghemoglobin protein from the roots of the soybean plant in food."

Impossible Foods can still sell its burger in public as FDA inconclusively stated that SLH is unsafe.