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Little Caesars is joining the plant-based protein trend with a pizza topped with non-meat sausage.

The pizza chain said Monday that it is testing out the Impossible Supreme pizza — topped with a meatless sausage made by Impossible Foods — in Florida, New Mexico and Washington state.

Consumers are increasingly interested in eating plant-based protein for health and environmental reasons, and the market for meat-like, but meatless, protein is growing. By 2023, the U.S. meat-substitute retail market could reach $2.5 billion, compared to $1.4 billion last year, according to the research firm Euromonitor International. Globally, the market could grow from about $18.7 billion in 2018 to $23 billion in 2023, according to Euromonitor International.

Restaurant chains are hoping to get a piece of that pie. Burger King, White Castle, Qdoba, Carl’s Jr., Bareburger and others sell items featuring plant-based protein in US markets. McDonald’s is selling a meatless burger in Europe, and Tim Horton’s recently announced that it is testing out three breakfast sandwiches with plant-based sausages made by Beyond Meat, Impossible’s competitor, in Canada.

The plant-based sausage is a first for Impossible, and was designed to appeal to Little Caesars customers.

Little Caesars started working with Impossible to develop a menu item featuring a plant-based protein in October, Ed Gleich, the pizza company’s chief innovation officer, told CNN Business. The company started paying attention to the trend earlier, when it noticed that more meat eaters were swapping out meat for vegetarian alternatives.

“These kind of flexitarians have been growing in nature,” he said. “They’re not hard core” vegans or vegetarians, but “they’re more adventurous” in their choices. The Impossible Supreme pizza is designed to appeal to meat eaters, and isn’t vegan (it’s topped with cheese, along with the fake sausage and other items).

Every Little Caesars product has to appeal “to our loyal, mostly carnivorous, fans,” said Little Caesars president and CEO David Scrivano in a statement, adding that “this is likely just the beginning of plant-based menu items from Little Caesars.”

At first, the plan was to add Impossible’s signature plant-based beef patty to Little Caesars pizzas. But Little Caesars shared with Impossible that more customers order sausage-topped pizzas than beef-topped pizzas, so Impossible came up with a new product. Gleich said he was pleasantly surprised.

“Normally companies want to sell you the product they have,” he said, “not a product they’ve got to get out and put some R&D time in, and put resources against and develop.”

Impossible customers have been asking the company to make a sausage product for years, Impossible CEO Patrick Brown said in a statement, adding that Impossible came up with 50 prototypes for Little Caesars.

Impossible’s protein is designed to be flexible and customizable, Impossible CFO David Lee told CNN Business. Seasoning and cooking methods can help make the protein taste and feel like a sausage, a burger, or something else.

Little Caesars plans to test the product for about four weeks in the three markets where it is available before deciding whether to roll out the product more broadly, Gleich said. If the chain, which has stores in 50 states, does decide to add the menu item to all locations, Impossible could struggle to fill the orders.

Impossible said last month that it is running out of product because demand for its patties is so high. Impossible serves about 7,000 locations, and that figure is expected to at least double this year as Burger King makes its Impossible Whopper available nationally.

To help meet demand, Impossible plans to open more manufacturing facilities and hire more employees. Recently, the private company announced that it has raised another $300 million in funding. It has raised over $750 million since launching in 2011.

But “we haven’t solved the problem” of shortages, Lee said, adding that he thinks Impossible will continue to struggle to meet “sky-rocketing” demand for some time.

“We are continuing to spare no expense and attempt to add capacity every day,” he said.

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