Fully ripe disease-free tomatoes are the best candidates for seed saving. Seeds can be saved casually by, for example, squeezing them out in a paper napkin and air drying them, but fermentation is a better route. It removes germination inhibitors and the gelatinous sheath from seeds, and it may treat some seed-borne diseases.
Here’s how it’s done:
*Cut tomatoes open– one variety at a time– and squeeze the pulp, juice, and seeds into a glass or plastic container.
*Fill the container halfway, but never add water as a substitute for tomato juice since water slows fermentation.
*Label and set aside the containers for 96 hours at a temperature not more than 70 degrees.
*Two or three times daily, stir the fermenting juices to submerge the pulpy material.
*After four days, fill the container with water, stir, and pour off the pulpy water, but not the seeds at the bottom.
*Repeat two or three times, and dump the seeds into a fine mesh sieve. Under running water, clean any fruit jelly and debris from the seeds with your fingers.
*Knock the strainer against the sink to remove excess water and quickly flip the strainer over, smacking it on a paper plate to deposit the seeds.
*Spread the seeds out on the plate and label it with the variety name and date.
*Let the seeds dry for 3 or 4 weeks in a well-ventilated place at room temperature.
*Put them in paper packets, and then in an airtight container that’s stored in a dark, dry place.
Believe it or not, refrigerated tomato seeds can be regenerated after 20 or more years when properly stored.