I use citrus zest in some of my beers (you should really use only fresh zest, not the whole peel, but that's another discussion). I put the zest in a weighted hop bag, with long string attached, in a jar and add enough vodka to cover and let that steep for a few days. The bag is weighted with glass marble-like beads used in flower arranging I got from a craft store. When I'm ready, I put the bag in the fermenter, using the string to suspend it roughly in the middle of the beer. I add the steeping vodka tot he beer as well. Then again, sometimes I skip the bag and just dump the steeped zest and vodka into the beer.