Martino's Roma Tomato (Solanum lycopersicum)

carefully selecting and saving seeds from their best plants, season after season. You can define ‘best’ to be whatever characteristic you’re after. Choose tomatoes in their prime. Since you’re just saving the seeds, you’ll get to eat most of the tomato anyhow, so this isn’t a real sacrifice. To maintain good genetic diversity, it’s best to save seeds from multiple tomatoes, and preferably from more than one plant of the same variety.

Cut the tomato in half and scoop or squeeze out the seeds and gel into a small container. Set the rest of the tomato aside for eating. Add 1/4 to 1/2 cup of water. Set the container aside, out of the sun, for 3 to 5 days. A moldy film will probably form on top.

To separate the seeds: First carefully remove the film. Then add some more water and stir. Good seeds will sink, so carefully pour off the water and the floating bits of pulp. Repeat until all the pulp is gone and you have clean seeds. Drain them as well as you can, then spread them in a single layer on a screen or a paper plate to dry.

Once the seeds are thoroughly dry, place in an airtight container for storage. Tomato seeds remain viable for years, even stored at room temperature

Information from Agriculture & Natural Resources, Cooperative Extension, Santa Clara County