Nutritional yeast is made from a single-celled organism, Saccharomyces Cerevisiae, which is grown on molasses and then harvested, washed and dried with heat to kill or "deactivate" it. It is inactive and therefore does not froth or grow like baking yeast does so it has no leavening ability.
Nutritional yeast is packed with nutrition, particularly B-vitamins, folic acid, selenium, zinc and protein. It is low in fat, is gluten-free and contains no added sugars or preservatives.
The vitamins and minerals are a definite bonus but the real star factor of nutritional yeast is its flavor, which has been described as cheesy, nutty and savory. Just a tablespoon or two can add richness to soups, gravies and other dishes. Larger amounts can make "cheese" sauces and eggless scrambles taste cheesy. It is also great on non-GMO popcorn. The most popular brand in health food stores is Red Star Flakes.