Impossible Burgers' additive that makes plant-based food 'bleed' needs more FDA testing, claims suit that questions whether 'heme' is safe to eat The Center for Food Safety claims not enough testing was done on soy leghemoglobin, which is genetically engineered for Impossible Burgers The color additive has the effect of making it seem like the plant products bleed The FDA approved Impossible Foods' use of heme in July 2019 Impossible Burgers are available across the country and are sold by prominent national restaurant chains, such as White Castle and Burger King