Saving seed is usually pretty straight forward....for instance a bell pepper. Scrape out seed, let them dry. Store. Easy peasy.
Not so with the beloved tomato.
Tomatoes come with a built in sprout inhibitor and need to ferment in order to easily separate the seed from the goo that surrounds them and achieve a better germination rate.
Yes.... "Goo" is a technical term.
Let's get one thing clear. You don’t absolutely have to ferment the seeds for them to be viable. But it makes the seeds much easier to separate from the gelatenous goo and eliminates a germination inhibitor. If you’re going to trade seeds with other people, it’s considered good etiquette to ferment your seeds.
Set the container aside, out of the sun, for 3 to 5 days. Once a moldy film of scanky nastiness forms on the top, you have achieved your goal.
To separate the seeds:
First carefully remove the film. Then add some more water and stir. Good seeds will sink, so carefully pour off the water and the floating bits of pulp. Repeat until all the pulp is gone and you have clean seeds.
Cut the tomato in half and scoop or squeeze out the seeds and gel into a small container. Add enough water to cover the seed and allow seed to settle to the bottom of container as they ferment.
Store the seeds:
Drain them as well as you can (a kitchen sieve works nicely) and blot with paper towels to dry as much water as possible. Then spread them in a single layer on a plate to dry. The seeds will stick to paper towels and paper plates. Spare yourself the agony and use a kitchen dinner plate. When the seeds are dry, store them in an envelope in a dry location. I have always used the crisper in the fridge to store my seeds, and I have always used a ziplock plastic baggie. Snack sized are so much fun! BUT the experts say use an envelope -- to each his own.