When you first get into making alcoholic beverages, the amount of information can be overwhelming. I want to clarify one group of additives that pop up from time to time, especially when making alternative kinds of wine.
Yeast nutrients are a source of nitrogen (from diammonium phosphate and urea) added at the beginning of brewing to nourished yeast culture with the most basic and essential nutrients for fermentation.
A yeast energizer also contains nitrogen elements but with additional trace nutrients (yeast hulls, magnesium sulphate, vitamin B complex) that spur on fermentation. You use a yeast energizer when a fermentation is “stuck” (it stops fermenting before you’re happy with the results).
You’ll find calls for these sorts of additives in brews that have a lot of sugar relative to nutrients. A standard beer or wine kit will have plenty of nutrients from the grains or grapes for beer or wine yearts.
A dandelion wine, ginger beer or mead, on the other hand, will have insufficient nutrients for these strains of yeast.
If you want to be frugal, save your “trub” (the hibernating yeast that sink to the bottom of your brews) and freeze it as a yeast nutrient for later brews. Make sure to add it during the boil so no surviving yeasts compete with your desired added yeasts.