I was wondering how small a batch of cider/beer I can brew in my primary? It's a 6.6 gal bucket and I usually brew 5-6 gal. I am interesting in trying cider or some flavored beer, but don't know if I want 5 gal at a time. I am worried if I do something too small it won't ferment properly and have enough pressure to push out the airlock. Any ideas? I've heard of trying a small Mr. Beer keg, but I can't get one right now. Thanks!