critterologist sent me seeds of a wonderful crinkley-leaved Italian basil strain years ago, and I've kept it going since (thanks again, critter). We had our first hard freeze a couple of nights ago, so the afternoon before I cut the basil stalks and brought them inside to freeze for use and to save seeds.
I've read that basil seed stalks should turn brown before seeds are collected, but I think that's wrong. By the time the stalks are brown, most all the tiny seeds are gone - scattered on the ground. Basil seed stalks are a bunch of tiny "bells", and each bell holds four seeds. In my experience, seeds are ready to collect when the seed stalks are still green but the seeds have turned brown/black (photo). Then I snip the seed stalks off with scissors and put them in a paper grocery bag. Keep the bag indoors for the winter, and by planting time next spring the seeds will shatter off and be in the bottom of the bag.
My wife and I save garden basil in ice cube trays, and she finds it real handy that way. I pick the wilting leaves off the stalks and we wash and dry them. Then I combine the leaves with just a little water and turn them into a mush in a small electric food chopper (photo). That mush goes into ice cube trays which we freeze overnight, then pop the cubes out into a zip-lock freezer bag and put back in the freezer. When my wife wants basil in a recipe, she simply opens the bag and drops a "basil cube" or two into the pot. Slick, huh?
