Saving tomato seeds is very easy and a great way to continue growing your favorite variety of heirloom tomatoes for years to come. By saving the seeds from the best fruits of the season, you are assuring the continuation of excellent fruit production in the coming seasons. You are selecting the best from your own particular growing conditions, not some generalized hybrid seed meant to be grown anywhere.
Here is all you need to do...
Squeeze the seeds from a tomato into a clean jar. Remember, use one of your top quality specimens.
Add some water to the jar...
Cover the jar with plastic and poke some holes in the plastic. Place the jar on a shelf out of direct sunlight for several days.
After three or four days a layer of mold will have formed on the surface of the water, and you will notice that the seeds have settled on the bottom. Use a spoon to remove the mold from the jar.
Now gently run water into the jar and carefully pour off the rinse water. The seeds will stay on the bottom of the jar as long as you pour the water off gently. Keep doing this until the water runs clear and all that is left is clean seeds. Pour these seeds onto a coffee filter. You can also use a paper towel, but the seeds tend to stick to paper towels.
Place the coffee filter on a plate and set it back on the shelf to dry for a few days. When completely dry, you can now store the seeds for next season. I usually just wrap them up in the same coffee filter and then put them into a white envelope. Make sure you label the envelope with the name of the tomato variety and the year you saved them.