Yeast energizer is a 5gm mixture of autolyzed yeast flakes, phosphate, zinc, vitamin b complex. Energizer gives the boost to the yeast to perform stress-free. Ideally, we use it for stuck fermentation troubleshooting.
Stuck fermentation means yeast stopped fermentation while the wine/beer is still too sweet. It can occur due to very low-temperature fermentation like in Lagers. In Barley wine, Porter and Sweet Port wine: high sugar concentration, or other stresses can cause incomplete fermentation. Must have for lagers, ice-wines, and other low-temperature fermentation. Also, yeast energizer removes the off-flavors in beer & wines that come from incomplete stressed yeasts.
Essentially for situations where the yeast often is not able to finish fermentation on its own. These vitamins and special foods are also used to make the yeast starter culture when trying to revive expired dry yeast sachets.
Please follow your recipe for the exact dosage. (~0.25-0.5 gm per liter for beer to 0.5-0.9 gm per liter for wine)