The Snarky Gardener shows you how to save tomato seeds using a 5 step process
1. Let the tomatoes ripen. The riper, the better. I usually seed save from tomatoes that are too far gone to eat. Remember, every year tomatoes fall off into the garden and “volunteer” the following season. What we are doing is speeding up the process by fermenting them in the house.
2. Cut open the tomato and scoop out the seeds. A spoon will be of good use to you here.
3. Put the seeds (and the pulp that will be with them) into a glass, mug, or jar. Add water. Cover with something that will let a little air in and keep the fruit flies out. For me, that means plastic wrap with a few holes poked in it. You will also want to mark each vessel with a label or write directly on it with non-permanent marker. It’s really easy to mix up multiple cups with tomato seeds in them.
4. Let sit for 3 days or so on a windowsill or somewhere else warm, swirling the “gunk” around once a day. You might notice some mold forming on the top. That’s to be expected.
5. After the 3 days, pour the liquid through a strainer and rinse the seeds carefully with water. Put the seeds at the bottom of the strainer onto a plate to let dry for a few days. For me, this usually takes a good “smack” to get the seeds onto the plate. I use plastic covered paper plates so the seeds don’t stick and so I can write on the plate what the seeds are. Again, it’s very easy to mix up your seeds, especially when you have 5 or 6 plates going at once. During the drying phase, you may want to break up any seeds globs that form so they don’t all stick together. The end result should be seeds that look like the ones you buy from a commercial seed house.