It is not uncommon for a gardener to save seeds of favorite vegetables for the next year. Saving tomato seeds may seem more challenging because of the slippery pulp that encases the tomato seed. Removing this pulp, which inhibits germination, is not difficult and will result in an abundance of seeds to plant next year to grow your favorite tomatoes.
Removing the Pulp
Choose a ripe tomato from a plant you want to save seeds from for next year. The tomato fruit needs to be ripe to very ripe so you know the seeds inside are fully mature.
Cut your tomato lengthwise.
Scoop out the seeds and pulp from the cut tomato. Try to remove as much of the pulp as you can at this time without loosing too many seeds. Put the remaining seeds and pulp into a clean wide-mouth jar, like a peanut butter, pickle or a mayonnaise jar.
Add to the seeds and pulp about 1/4 cup water and screw on the jar lid. If you do not have a lid, you can put a layer of foil over the jar opening and secure it with a rubber band.
Place the jar in a warm spot. The warmer the temperature is during this fermentation period, the faster the pulp breakdown will happen. Ninety degrees F is ideal, but lower temperatures only mean it will take longer for the fermentation. During this time, take the lid off and stir the water and tomato pulp mixture every day. After two to seven days, depending on the temperature, you should see bubbles, the seeds settling to the bottom, and possibly a layer of mold on the surface. When you see the bubbles and seeds on the bottom, the pulp has separated from your tomato seeds. Add enough water to double the mixture and stir well; this will stop the fermentation process.
Skim off the pulp debris at the surface of the mixture with a spoon. Continue to stir and skim off the debris until only the seeds and water remain.
Drying the Tomato Seeds
Rinse the remaining seeds thoroughly, using a sieve.
Place your cleaned tomato seeds on a paper towel. Spread the seeds evenly and in a single layer over the paper towel.
Put the paper towel in a warm, but not hot, location. Too hot of a location, over 95 degrees F, will effect the germination of your seeds next year. Dry your tomato seeds for at least one week. You can check the dryness of your seeds by testing their hardness. If the seeds are too hard to bite or smash, they are dry enough.
Roll up the seeds in the paper towel. Store the paper towel with seeds in an airtight container. Label the container and place it in a cool place until you are ready to plant your tomatoes next year.