Choose ripe, healthy tomatoes from disease-free plants
Cut the tomato open and scoop out the seeds with the surrounding gel
Place the seeds and gel in a clean jar or container
Add a small amount of water if needed to cover the seeds
Let the mixture ferment at room temperature for 2 to 4 days
Stir once a day and wait for mold to form on top
Add water, then pour off the floating pulp and bad seeds
Rinse the good seeds thoroughly in a fine strainer
Spread the seeds in a single layer on a paper towel, coffee filter, or plate
Dry the seeds completely in a cool, shaded, well-ventilated place
Store the dried seeds in a labeled paper envelope or airtight container
Keep the seeds in a cool, dry, dark place until planting time