(Editor's Note: this article was originally published on March 10, 2007)

I love the idea of self-sufficiency in the garden, and heirloom/open-pollinated varieties of vegetables fit very well into that mind frame. One of the many benefits of heirlooms is that you can save the seed from each crop you grow and use them the following season. Unlike hybrids, which force you to buy new seeds each year, heirlooms will always produce the same fruit year after year, giving you true self-sufficiency in this area.

Saving seeds from tomatoes, however, is far from intuitive and many methods have been used to varying levels of success. Behold now as I forever put to rest the mystery of tomato seed saving as I unlock the mystery of fermentation!

So, you've harvested a bunch of tomatoes, and you are ready to save the seed. In addition to the tomatoes, you will need a clean knife and jar or cup, as well as a sharpee-type marker.
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Remove the stem from each fruit and turn it over so the bottom is facing up. Then take your knife and make a small cut in the bottom of the tomato.
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Now squeeze the insides of the tomato into a clean container. I use 16-ounce disposable plastic cups for this purpose. When squeezing the insides, you want to get all the seeds and pulp into the cup. Once the seeds are removed, use what's left of the tomato for fresh eating or making salsa (is there any other use for tomatoes?)
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Make sure the container is marked with the type of tomato grown, as well as the date that you harvested these tomatoes. The fermentation process is a bit lengthy and, while you THINK you will remember what variety is in that cup, you can't rely on your memory (trust me on this one). So get your marker out and mark that cup.

Depending on the juiciness of the tomato being processed, you may need to add a little water to give the whole mix a nice soupy consistency. It doesn't hurt the process if you add a bit more water than needed. In the case of the Tiny Tiger tomatoes used in this illustration, I did not need to add any water.
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After a couple days, you should notice a lovely white froth developing on the top of the mixture. This exciting display means that fermentation is well under way and you may now begin dreaming of next year's salsa.
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Once the froth has developed, I like to give it a good stir once or twice a day. This seems to encourage the seeds to seperate from the pulp a bit.
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When the fermentation process has gone for several days, give it one last stir and then fill the container the rest of the way, all the way to the brim, with water. Then stir gently and wait about 10 seconds for the viable seeds to settle on the bottom. Then pour out the top half of the liquid, being careful to avoid dumping the good seeds that sunk to the bottom. The floating seeds on top are bad seeds and deserve to be thrown out with the bathwater.

Then fill it up to the top again, stir, wait, pour out half. Repeat. Repeat again. Repeat again. Yes, repeat again. You will notice that each time you fill and dump, your water will become clearer and clearer and the pulp will eventually be gone. Repeat that process as many times as needed until the water is crystal clear and all you have left is clean water and millions of seeds in the bottom of the cup.

At that point, carefully pour out almost all the water, then dump the seeds out onto some wide container. I use styrofoam dinner plates.

Wick off the excess water from the plate using a paper towel and then spread the seeds into a thin layer. Let dry in a shaded area, out of direct sunlight (I put on my fridge). When they are completely dry, you'll have a big cake of tomato seeds. Rub the cake between your fingers to separate the seeds from each other, the package them up in labeled envelopes and then head directly to the DG Tomatoes forum and trade your seeds for even more heirloom varieties!

Quick note: when I save tomato seeds, I do my best to obtain an equal amount of fruit from ALL the plants of that variety that I grew. This way, I get a diverse group of genes. It also goes without saying that in order to maintain seed purity, you shouldn't grow tomatoes of differing varieties close to each other. I recommend the book "Seed to Seed" to learn about seed purity. Have fun. :)