Sunflowers are mature when the back of the head turns yellow and the seeds take on a brownish tinge. If birds begin to pick at the heads before they are mature enough to cut, tie a perforated plastic bag over the head. When the heads are mature, pick them and hang them upside-down in a warm, dry place. When the head is dry, the seeds separate easily. Be sure the seeds are fully dried before putting them in air-tight containers for storage.
Sunflower seeds can be roasted by heating them in a 300 degree F oven for 15-25 minutes. If you want salted seeds, soak them overnight in a brine of 2 tablespoons of salt to 1 cup of water. Boil the seed brine mix for a few minutes and drain. Spread the seeds thinly on a cookie sheet and roast in a 200 degree F oven for 3 hours or until crisp. If roasted long enough, they are easy to shell.
For more information, see the following Planttalk Colorado™ script(s).