I always use yeast nutrient, yeast energizer & a little extra D.A.P. (diammonium phosphate) in my fermentations whether I'm making cider, wine or mead. I'd rather spend the extra 25 cents & add the stuff rather than not add it & run the risk of getting off flavours from stressed yeast. There are certainly nutrients in fruit/juice, but there may or may not be enough, or maybe not the right type for the particular strain of yeast. Some strains need more nitrogen than others, especially wine yeasts. I'm not as familiar with beer yeast, but I'll wager they would also benefit from aded nutrients, especially when they're fermenting things other than what they were bred for. Regards, GF.