Impossible Foods discovered a scalable, affordable way to make heme without animals: the company engineers and ferments yeast to produce a heme protein naturally found in plants, called soy leghemoglobin. The heme in the Impossible Burger is identical to the essential heme humans have been consuming for hundreds of thousands of years in meat — and while it delivers all the craveable depth of beef, it uses far fewer resources.

This transition follows a months-long review of White Castle's supply chain, and is an issue the company has been working alongside The Humane Society of the United States to address since last year.