When grating citrus fruits for zest, make sure you only get the coloured part of the peel. Don’t go all the way through to the white pith; this will taste unpleasantly bitter. It’s possible but difficult to do this with even the sharpest of knives; I recommend getting a proper zester even if you only use it a few times a year. Traditional zesters
are good for doing a couple of fruit but can get tedious if you’re doing a large batch of zest. I’m a big fan of Microplane and their coarse grater should give you a good amount pretty quickly.