Nutritional yeast gives this 100% plant based cheese sauce much of its cheesy flavor. Nutritional yeast adds a surprising "cheesy" flavor to foods and mimics the umami flavor often derived from parmesan or cheddar cheese. Starch and vegetable oil or vegan butter are also important to the texture of this cheese sauce. This is important because one of the biggest components of taste is texture. Even if the flavor of a food is good, if the texture is "off" it will affect how we feel about the food's flavor.