Campden tablets are used to inhibit bacterial growth. I use them when I use berries in my wine too. Defrost, crush a couple up and toss em in, seal sanitized container and leave it for 24 hours. Probably overkill since the berries are already sanitized (storebought) but if using fresh berries they're a must(haha get it?). Anyways, they're fine and dandy, like sour candy.