Yeast is the single-celled microorganisms that are responsible for fermenting sugar (maltose, glucose, fructose, sucrose, etc.) to ethanol. In the absence of oxygen, these yeasts do the transformation which converts your grain/fruit into a beverage. Yeast nutrients, on the other hand, are food for the yeast. On their own nutrients achieve nothing more than making a comfortable home for the yeast to function at its best capacity. Yeast energizer, on the other hand, is an SOS remedy needed to recover from stuck fermentation or incomplete fermentation or excessively low-temperature fermentation which can make yeast sluggish.
Although Yeast Energizers are types of nutrient blends, they also contain components such as vitamin B, diammonium phosphate, tricalcium phosphate, magnesium sulfate, and yeast hulls. Yeast energizers are particularly useful to restart a Stuck Fermentation, as it allows yeast populations to increase in a batch of beer or wine which likely has been depleted of these components due to an earlier yeast population growth. The additional components included in Yeast Energizers are most effective when for high gravity fermentation (high sugar high alcohol), low-temperature lagering, excessively low pH, high ash content (molasses) and other extreme fermentation styles.