It features the same burger build as the store's traditional beef-based Whopper, replacing the patty with Impossible Foods' plant-based version. It also contains tomatoes, lettuce, mayonnaise, pickles, and sliced white onions on a sesame seed bun. Mayo can be removed to make the option free of animal ingredients.
The sandwich initially launched in 59 stores around St. Louis in Missouri on April 1. According to BK bosses, the launch 'exceeded expections', and went on to roll out across all of Burger King's 7,000 US outlets.
According to a Burger King spokesperson: "[The Impossible Whopper has] become one of the most successful product launches in brand history, leading to outstanding comparable sales of positive five percent this past quarter."
Burger King appears to be trying to capitalize on this success by trialing a further trio of sandwiches featuring the Impossible Burger in the States.
These include The Impossible Whopper Jr. - a smaller version of the Whopper, The Impossible Burger featuring ketchup, mustard, and pickles on a sesame seed bun and The Impossible Cheeseburger with all the above ingredients plus dairy-based cheese.
The new sandwiches have been added to the menu of 180 test locations in Milwaukee, WI, Cedar Rapids, IA, Augusta, GA, Cincinnati, OH, and Buffalo, NY.
In addition, the chain is also testing meatless options in Europe. It recently launched its 'Rebel Whopper' - featuring a plant-based patty from The Vegetarian Butcher - in more than 2,500 restaurants in 25 countries across Europe (the Impossible patty has not yet been approved for use in Europe).
The Rebel Whopper features the same burger build as the store's traditional beef-based option - tomatoes, lettuce, mayonnaise, pickles, and sliced white onions on sesame seed bun. Mayo can be removed to make the option free of animal ingredients, though it is not vegan as the patty is cooked on the same grill as meat.
According to the fast-food giant, Burger King UK 'is not launching the Rebel Whopper just yet, but it will be coming soon'.
'Plant-based not vegan'
While some vegans have embraced the burger, ordering it without mayo as an animal-free option, others have chosen to eschew it because of Impossible Foods' history of animal testing.
Impossible Foods itself describes its patty as plant-based rather than vegan because one of its ingredients - soy leghemoglobin aka 'heme' - was fed to rats in order to test its safety. In excess of 180 rats were killed as a result of the testing.
When the testing became public knowledge, Impossible Foods CEO Pat Brown, a vegan of more than 16 years, published a statement titled The Agonizing Dilemma of Animal Testing.
In it, Brown said the core of his company's mission is to 'eliminate exploitation of animals in the food system', as well as reduce the impact of animal agriculture on the environment.
"Among the thousands of animal species surveyed every decade by the World Wildlife Fund, the total number of living individual wild animals today is less than half what it was 40 years ago," he wrote.
"This wildlife loss is overwhelmingly due to the exploitation of animals for food, including hunting, fishing and especially the replacement of wildlife habitat by animal farming."