I have had some students ask me how to save tomato seeds for next year's planting. Last week when my mom was collecting tomato seeds I took a couple of pictures so you can see how she does it. It is actually a very easy task. My mom has saved our tomatoes seeds ever since we moved to the Bay Area from Calabria in the 70s. We still grow the same San Marzano variety that we brought with us. Every year she picks the best-looking tomatoes from which to harvest the seeds.
Cut a ripe tomato in half and using only your fingers remove the seeds with the gelatinous stuff around them and place them in a fine mesh strainer.
Rinse the seeds under running water. Move them around to remove any of the gel that might still be clinging to the seeds.
Once the seeds are clean place them on thick paper, like a grocery bag or a paper plate.
Spread them evenly and make sure they are all in one layer.
Allow them to dry thoroughly, keeping them away from direct sun. Three or four days should do it, although my mom usually lets them dry for a week. The seeds will stick to the paper, so carefully loosen them.
You should store the seeds in an air-tight container, like a small glass jar or paper bag or even a plastic 35-mm film container. Make sure you put the containers in a cool, dry place. Also, remember to label and date your seeds so that you will have them ready for next spring's planting.