The yeast is generally sterilized around 250 F (121 C) for about 20 seconds, then dried.
Some Inactive Yeasts are used commercially as “dough conditioners” — to help the dough relax and stretch.
Nutritional yeasts are yeasts, grown specially for their nutritional value in a nutrient mixture of molasses, then killed through sterilization, dried and sold in powder and pill format. Beyond the nutritional value in the yeast, they are also often supplemented (e.g. vitamin B12 is often added to give it a full range of B vitamins; vegetarians are often lacking in B12, which we otherwise get from meat.)
Nutritional yeast differs from brewer’s yeast in that while nutritional yeast is purpose grown, brewer’s yeast is a by-product of the beer brewing process. After being used about 5 or 10 times, brewing yeast has no more life left in it and dies. This yeast often has a bit of a bitter taste to it.
Nutrition
Some people say you should never eat live yeast, as it will grow inside your intestines, consuming nutrients that your body should get. Others advise that live yeast products, such as Kefir (which contains Saccharomyces kefir and Torula kefir yeast strains), are good for you. Home brewers disagree on whether drinking the dregs containing live yeast is good for you, or gives you diarrhea.
Equivalents
1 tbsp of powdered = 2 tbsp flaked