Nutritional yeast, unlike other yeasts used to brew or bake, is dead (i.e. inactive). It kinda sounds like a weird thing to eat, but it actually has a wonderful savory umami flavor. Plus, among other nutrients, it contains essential amino acids and is usually fortified with B vitamins.
Nutritional yeast can be incorporated into sauces, soups, and other savory dishes for flavor, or even sprinkled directly on top of finished foods like baked potatoes or popcorn. It’s also often used in vegetarian and vegan cooking to simulate or replace cheesy, eggy, or chicken-like flavors, such as in this vegan “chicken” soup.
Nutritional yeast is usually sold either as flakes (pictured above) or as a powder. It’s the same stuff, but measures differently because flaked has so much more air space due to it’s chunky shape. If subbing powdered for flaked, use about half as much as the recipe calls for. If subbing flaked for powdered, us about twice as much as the recipe calls for.
A helpful tip when working with nooch (especially powdered) is to try not to inhale it! It’s not dangerous or anything, but for some reason it’s really good at making you cough.