Burger King is serving a version of its signature sandwich made from cows that spew less methane, a nasty greenhouse gas that’s contributing to climate change.

The cows that produce the special patties — which go on sale in five cities Tuesday — are fed with a special diet that the Restaurant Brands International-owned chain developed in an effort to lighten its environmental footprint.

Burger King’s research in collaboration with scientists from the Autonomous University at the State of Mexico and the University of California, Berkeley yielded a simple secret: Adding 100 grams of lemongrass leaves to cows’ daily diet in the last four months of their lives can cut the amount of methane they fart, burp and poop into the air by up to a third.

The fast-food giant said it’s making its findings public so other companies can slash methane emissions, a crucial step in curbing climate change. Livestock account for 14.5 percent of the world’s total greenhouse gas emissions, according to the United Nations Food and Agriculture Organization.

“This an open source approach to a real problem,” Fernando Machado, global chief marketing officer at Restaurant Brands International, said in a statement. “If the whole industry, from farmers, meat suppliers, and other brands join us, we can increase scale and collectively help reduce methane emissions that affect climate change.”

The “Reduced Methane Emissions Beef Whopper” will be available while supplies last at five Burger King restaurants in New York, Los Angeles, Austin, Miami and Portland, Oregon.

Burger King has also rolled out a meatless Whopper made with patties from Impossible Foods, which says its product generates 89 percent fewer greenhouse gas emissions than ground beef from cows.