Brewer's yeast is an inactive yeast is rich in protein and B vitamins which is used as a nutritional supplement. It is a deactivated form of beer yeast and as a by-product of beer-making, it has a slightly bitter flavor. If you object to the bitterness, try nutritional yeast, which is made from the same yeast strain but grown on molasses. It's more expensive but has a more pleasant flavor. You can also buy debittered brewer's yeast. Brewer's yeast comes powdered (the most potent form), in flakes (best for health shakes), and in tablets. Don't confuse this with active forms of yeast, like the kinds bakers, brewers, and winemakers use. If you eat them, active yeasts will continue to grow in your intestine, robbing your body of valuable nutrients.