When it comes to saving heirloom seeds tomatoes in my opinion can be some of the easiest seeds to harvest and save. The process is relatively straightforward and works with all varieties of tomatoes. The first thing you'll need of course is a ripe tomato even overly ripe is okay. Below I've listed the other items you will need to save tomato seeds.
*Clean glass jar with a lid
*Label for your jar
*Coffee Filter or paper plate
Okay so once you have everything you need the first thing you'll want to do is cut the tomato horizontally to expose the seeds pits that surround the core.
Then fill your glass jar about half way with water. Once you have your jar ready simply squeeze the tomato over the jar as seen in the picture below.
You can also use your knife to dig around in the seed pits to remove any tomato seeds that did not originally come out.
After you have removed all the tomato seeds you can then add the lid to the jar and shake it lightly. And if you haven't already, you'll want to add a label to the jar. This especially important if you have other varieties you are saving as well.
Then place the jar out of direct sunlight for three to four days. Also loosen the lid slightly so the jar can breathe and allow fermentation to occur more readily. The fermentation process is needed to break down the gelatinous material that surrounds the tomato seed.
If you like you can gently tighten the lid and shake the jar for a few seconds each day, just make sure to loosen the lid before putting them back up.
Once you are ready to clean the seeds simply tighten the lid on the jar and shake it once last time. After you have shaken the jar go outside and remove the lid and pour off the top liquid. I say go outside because the smell can be quite atrocious! Then once you have completed the last few steps pour the remainder of the jar into a fine mesh strainer and rinse with cold water. You can lightly rub the seeds against the mesh to remove any trash remaining.
By now most of the material left in the strainer should be the seeds themselves, but it's okay if a little flesh remains. You can either leave them in the strainer to dry or you can remove them and place them on coffee filters or paper plates. I don't recommend paper towel because after drying for a while the seeds may stick. Once the seeds are good and dry put them into either a small sandwich bag or paper envelope for later planting.
It's that simple! And again this method works for all tomato varieties. Well that pretty much sums up how to save tomato seeds, but if you have any questions feel free to ask.
Thanks for reading and Happy Gardening!