Burger King is trying to save the environment one cow at a time.

Cows release large amounts of methane, a greenhouse gas that traps the sun’s heat and contributes to global warming. Livestock represent roughly 14.5 percent of greenhouse gas emissions, and within that amount, 41 percent comes from beef production, according to the Food and Agriculture Organization of the United Nation.

To combat this problem, the fast-food chain worked with scientists to test and develop a new diet for cows that reduces their methane output. Alongside researchers from the Autonomous of the State of Mexico and U.C. Davis, Burger King refined a new menu for cows. The researchers discovered that by adding 100 grams of dried lemongrass leaves during the three-to-four month “fattening” stages of production, daily methane emissions dropped as much as 33 percent on average.

“Beef is one of the top commodities that we buy at Burger King,” said Matt Banton, Burger King’s head of innovation and sustainability, in a statement. “We also know that cattle are one of the top contributors to overall greenhouse gas emissions, so our job is to understand how we can continue to grow our business while still reducing the emissions from cattle over time.”

On Wednesday, certain Burger King units in Miami, New York, Austin, Portland, and Los Angeles will offer the Reduced Methane Emissions Beef Whopper sandwich, sourced from cows with lowered methane emissions.  

Burger King made the research publicly available so other brands, suppliers, and farmers can test, replicate, and refine the process.

“RBI’s Sustainability strategy is grounded in one simple principle—doing what’s right,” RBI CEO José Cil said in a statement. “And this project is a really good example; it’s a scalable solution to help reduce methane emissions.”