Burger King will begin selling the plant-based Impossible Whopper across the US next week after a successful run in six regions.

The rollout to 7,000 locations will be for a limited time, a typical practice in the fast-food industry for new products. The chain will not say how many of the burgers it has sold since introducing them in April, but did say it was enticing more people to enter its stores.

Impossible Foods, the company that makes the burgers for Burger King and White Castle, is struggling to meet surging demand. On Thursday, it announced a new partnership with OSI, one of the world’s largest food producers.

Impossible Foods has doubled the workers at its plant and produced a record number of burgers in June, but demand is still outpacing production.

Impossible Foods introduced the burger as the veggie patty that “bleeds” at the high-end New York restaurant Momofuku in 2016. The burger is a feat of food engineering, attaining its red color from genetically modified yeast.

Demand for plant-based meat alternatives has surged in the last two years as companies pitch the products to consumers conscious of meat’s contribution to the global climate crisis.

The company’s largest rival, Beyond Meat, went public this summer, growing sales and its stock price rapidly after entering the stock market. Beyond Meat’s sales are also buoyed by a patty – the Beyond burger.

Both Impossible Foods and Beyond Meat are competing to offer their products in fast-food chains and directly to consumers – and struggling to meet demand.

Just eight days before Burger King announced the Impossible Whopper, Dunkin’ announced it would offer Beyond Sausage patties on breakfast sandwiches in New York City. Only one day earlier, the US Food and Drug Administration approved Impossible Foods’ products for sale direct to consumers, after it approved leghemoglobin as a color additive.

The Associated Press contributed to this report