I've saved my tomato seeds using fermentation for years. It's easier to do than you think. Just scrape all the seeds and pulp into a cup, set the cup outside and in 2-3 days (depending on the temp, the hotter the quicker the mold forms) there should be a layer of gross mold on top. Good seeds will be at the bottom of the cup, debris and immature seeds will float. Pour out mold and rinse out the seed water until it's fairly clear. Dump entire contents into a mesh strainer and blast them with a strong stream of water. Using a spoon I scrape and spread them into a paper plate. Days later sit down and break up dried clumps of seeds and bag them up.
