Brewer's yeast requires an adequate supply of vital nutrients and trace minerals in order for it to carry out a healthy fermentation cycle. The nutrients and trace minerals the yeast needs are naturally present, in adequate quantities, in malted barley or manufactured by enzymes during the malting or mashing process.
The addition of extra-prepackaged yeast nutrient to all malt extract beers is unnecessary. The only time that a home brewer needs to consider its addition is if you've used more than 40 percent adjuncts-that is, ingredients other than malt extract or malted barley. Yeast nutrients are recommended when making mead and wine.