Fermenting accomplishes several things. First off, all of the gunk surrounding the seed gets removed, including the anti-germination compounds found in the gel. Viable and non-viable seeds get seperated. And seed-borne pathogens are destroyed.

 

Because tomatoes are in-bred, you can, in theory, just save seed from one fruit. But to be safe, you should save seed from the fruit of at least three plants.

 

Fermentation is the height of simplicity.

 

Start by removing the seeds, juice, and gel coat into a waterproof container. I use the cheap, throw-away plastic drinking cups available everywhere. Most people merely squeeze the tomatoes into a container. I prefer not losing the flesh, so quarter them, remove the seed mass with a spoon, and freeze the flesh until there's enough to make sauce.

 

Once you have the container of seed, add an equal volume of water. Then set the container in a warm place (but not in direct sunlight), stirring it once a day. Fermentation takes 5-7 days. You sometimes can actually see bubbles rising as it happens.

 

All of the debris---the dissolved gell coat, no-viable seeds, other crud will float on the surface. You may even see a white mold form. Viable seeds will sink to the bottom.

 

Once the process is complete, clean the seed. Gently fill the container with water and pour off the mold and crud. Rinse the viable seed several times to remove as much non-seed stuff as possible. Most folk stop here. I pour the seed into a very fine mesh strainer and, under running water, gently rub the seed against the mesh.

 

Drain the seed and spread it on a paper or foam plate. Set aside in a warm place to dry. As it dries, rub the seed between your fingers and the palms of your hands, to seperate it as much as possible.

 

When fully dry (depending on conditions, 2-4 weeks) package and label the seed.

 

Depending on variety, tomato seed remains viable for 4-10 years.