Nutritional yeast is deactivated (dead) yeast — almost always the species Saccharomyces cerevisiae, the same microbe used to leaven bread and ferment beer — grown for food, then heat-killed, washed and dried into pale-gold flakes, granules or powder. Naturally rich in B-complex vitamins and complete protein, it carries a savoury, cheesy, nutty umami flavour and is a staple seasoning of vegan and vegetarian cooking, sprinkled on pasta, popcorn and salads or stirred into sauces in place of grated cheese.