Pick fully ripe, healthy tomatoes from the best-looking plants.

Cut the tomato in half (horizontally across the equator).

Scoop the seeds and surrounding gel into a clean jar or cup.

Ferment the seeds by adding a little water to the jar, just enough to cover the seeds.

Loosely cover the jar (with a paper towel or coffee filter).

Leave it at room temperature for 2–4 days, stirring or swirling once a day.

You'll notice bubbles, foam, maybe a little mold and a slight odor, this is normal!

After 2–4 days, fill the jar with water. Stir well, then let it sit for a few seconds. The good seeds sink, while pulp and bad seeds float. Pour off the top layer (pulp, mold, bad seeds). Repeat rinsing 2–3 times until water is clear.

Pour off the clean water and spread the seeds on a nonstick surface so they can dry.

Let them dry for 5–10 days in a well-ventilated, cool, dark place. Stir daily to prevent clumping and mold.

Store in a paper envelope or glass jar with a tight lid. Label with variety name and date.

Keep in a cool, dark, dry place (or refrigerator if storing long term).