Harvest squash seeds from fully mature squash. According to the website, What's Cooking America, squash is mature 50 to 55 days from planting. Winter squash varieties include Fairy Tale Pumpkin squash and Buttercup squash. Summer varieties include Delicata squash and Banana squash. The best time to harvest all squash is after autumn's chill sets in. Within that time frame, you have plenty of time to allow any variety of squash to mature.
Allow squash to go to seed on the vine. Rather than pick squash at the peak of ripeness, allow it to go to seed. Harvest squash when the skin is very hard and textured. Leave picked squash in the sun to dry. This curing process takes about three weeks and allows seeds to ripen.
Set the squash on a large cutting board. The skin will be quite hard. Chop the squash in half with a heavy knife.
Remove mature seeds. Mature seeds are hard and thick. Scoop out the seeds and rinse in a strainer. Remove all fibers under warm running water.
Dry seeds with a smooth towel. If you plan to roast the seeds, you can do so immediately after extracting them from the fruit. To save for next year planting, spread dry seeds on a cookie sheet or other flat surface. Once the seeds are dry, store in glass jars in a cool dry location.