Aside from using finely grated citrus rind in recipes, I also make Chocolate Coated Citrus rind. I remove the rind in segments (which give more evenly-sized pieces when coated with chocolate) - it's easy to scoop out the pith with a teaspoon this way, too. Then I freeze it in a plastic bag until it's required. Some of it I'll put through the food processor - just a zap or two will give 'finely grated' - and I put that into a separate plastic bag and freeze it. I make sure that it's packed flat and thin, like a pancake. You can make several 'pancakes', divided by plastic wrap. That way, it's easy to break off a piece of the required size - if you freeze it in fat lump, you'll need a hammer and chisel! Then back into the freezer until next time. You can also cut the rind segments into very thin strips for garnishes etc and freeze them separately, if desired.