I am just getting into home brewing and I'm interested in brewing very small (1-gallon) batches at a time. It seems that using a full pack of yeast (typically pitched into 5 gallons) is overkill, and I'm wondering if there are such things as prepackaged yeast in very small quantities. I was told that I can use a whole pack in my 1 gallon jar, but I'd like to either use smaller quantities or at least make the full package of yeast last for multiple batches. I assume that once a packet of yeast is opened, it must be used immediately. Am I right? I wish there was a way to store leftover yeast for future use. Any ideas?