My 5yr. old saved an heirloom 3lb Lithuanian tomato seed, that I almost threw in the garbage, thinking it to be of no good use. She sprouted them the following year and we planted them in the garden next to an orange type we like. She ended up with a variety of her very own now that we named after her, the Daisy Mae! They grow to 2-3 lbs in size and as orange as the sun. The pick below says it all! She's learning and loving it!
To begin saving tomato seeds, just squeeze out the "innards" of your best looking tomatoes, into a cup that you write on with a permanent marker. Pics at bottom show cup full of moldy stuff, that's what you want. The fermentation breaks down that gel sack.
Labeling is real important to figuring what's in there in a few days, trust me on this. We have neglected to label and it doesn't turn out good to guess at which color cup had what. Especially all filled with scum! Also they should be open pollenated not hybrids. Hybrids will not grow out true, most of the time. Next cover with water, this will need to sit a few days to form a bacteria (rot) that will eat away the gel sack on the tomato seed. I let it sit for three or four days on top of frig where temp is slightly warmer and Viola! You've got scum. Just what company wants to see, lots of cups or bowls growing mold in your kitchen, ha ha. Ok, getting on with it. Then just dump into strainer and rinse all scum away. Wash thoroughly with cold water and place on napkin-ish thing to dry. I don't use much paper products (big $$$ out the window) so here I used a coffee filter. You get hundreds on the dollar so I splurged and used these. Paper plates will spill, and napkin-ish items (you could even use a wash cloth) hold onto the seed slightly and give you something to write on. You again must label for after it dries, you will want to know what it is. Label, label, label! Trust me you will be super disappointed if you don't and can't remember which is which. Or just say it's a surprise, which we do that also. When the seeds end up growing out you may see label rubs off or gets sun bleached or what not and so it just goes in the surprise section of the garden. When they are TOTALLY dry, remove and place in sandwich Baggie with label, the put into a larger FREEZER bag. It really does need to be freezer so to keep out as much moisture as possible. Here is my collection of heirloom seeds all first individually bagged then in all together in a larger bag in which I keep a little silica packet (from a shoe box or vitamin bottle) and this keeps in the freezer for years These are the exact same steps for saving Cucumber seed, non-hybrid. They are also seeds in cased in a gel sack and must be fermented. If a six year old can do it you can too!