Think of this as a multivitamin for your yeast. It's a mix of nitrogen, zinc, amino acids and vitamins that gives your yeast everything it needs to get through fermentation without struggling. You don't need it for every brew, but it's worth having on hand for the bigger stuff - high-gravity beers, brews with a lot of adjuncts like corn or rice, or if you're re-pitching yeast that's already done a job of work and could use a pick-me-up. It won't make fermentation go faster, but it helps stop it stalling out before it's done, and tired, stressed yeast is often where off-flavours come from - so this is cheap insurance against that. Just stir it into your wort before you pitch, or add it to a yeast starter if you're making one. Each pack is sized for a standard 23L batch.