I have collected over 10000 tomato seeds, for the first time, this year. In order to collect tomato seeds to be used in your garden the following year, you have to first ferment them.
A tomato seed is typically encased in a gel sac. The gel sac prohibits germination. Think about it. The tomato is mostly water and the seeds sit in the tomato at a cozy 80 degrees or more. The tomato itself is a perfect environment for seed germination. The tomato naturally suppresses germination by encasing the seeds. When a tomato rots, it typically is fermenting. The get sac gets dissolved and the seed is now free to germinate. You have to create this process so the tomato seeds will be ready for germination when you need them.
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Step 1: The Jar, the Gel Sac, and Tomato Seeds
You will need a jar with a lid. You can use whatever you would like. The fermenting seeds will smell badly and a tight lid is a good way to manage the smells.
The get sac is the sac that surronds a tomato seed. You can see them easily with the naked eye. They easiest way to collect the seeds is to cut up a tomato and scrape the seeds and the tomato gel and liquid into a large bowl.
You WANT the tomato liquid and gel mixed with your seeds. The seeds need to ferment in the liquid. Try and keep out larger pieces of tomato if you can. The pictures will show you the seeds surrounded in a gel sac and basic other steps.
Step 2: Scrape the Tomato Seeds Into a Bowl and Pour Them Into the Jar
There are no style points for this process. It is a bit messy. Just fill your bowl with the tomato seeds and tomato liquid. When you reached your goal, pour the mix of seeds and liquid into the jar.
The important part of this step is to make sure there is enough liquid in the jar with the tomato seeds to allow the contents room to separate during the fermentation process.
If the jar is about 1/2 full with tomato liquid then add some water to fill the jar to about 3/4 quarters full. If the jar is under 1/2 full then add water to fill it to 1/2 full. You can't really mess this up so don't spent too much time stressing about it. My jars are often nearly full to the top because of the tomato liquid.
The pictures are of different points in the fermentation process.
Step 3: Seal the Jar and Let It Ferment for 5-7 Days
Different recipes will tell you different time frames for the fermentation process. I found 5-7 days to be fine. If this is your first time, let them go 7 days. With experience you will be able to eye-ball the seeds and tell when they are ready.
Once sealed in the jar, the fermentation starts within 48 hours. Give the jar a brisk shake each moring. The goal is to remove the gel sac from the seeds. A little agitation helps. On the second day you should notice bubbling and there will be pressure released when you open the lid. So, you do need to open the lid on the second day and smell. It should smell sour and foul. That is GOOD!
You will also notice the liquid and seeds stratify. That is also good. You will see your seeds float to the top. They are most likely your healthy bunch. The other stuff in there will soften and decay and sink. After 7 days you will clean up the seeds.
Step 4: After 7 Days, Pour the Contents Into a Sieve and Rinse
In 7 days you will have tomato seeds that are ready to be cleaned and then dried. You should purchase a fine mesh sieve that won't let the seeds through. Pour the contents into the sieve and rinse with cold water. You will have to GENTLY rub the seeds along the sieve. The tomato matter left, is decayed, and will easily press through the sieve leaving you hundreds of tomato seeds. Rinse them well with cold water.
Step 5: Dry the Tomato Seeds and Label Them
Tomato seeds will dry and stick strongly to paper towels and napkins. So beware and use coffee filters for the drying process. To set up the seed drying, get a plate and line it with 2 or 3 paper towel sheets. Put the tomato seeds on the coffee filter and spread them out and sit the filter on the paper towels. The water will be wicked away.
The drying process is important. You want to let them dry 7-10 days. Make sure you spread them out nicely on the coffee filter.
And don't forget to label the paper towels. You will forget what is what if you do more then one variety of seeds.
Step 6: Store Your Tomato Seeds
You can store your tomato seeds in anything really. The best practice is a sealed container, in the dark and in a cool place. It doesn't have to be the refrigerator. Make sure you label your containers.
Test germination is also something you can do. In brief, just place some tomato seeds in-between damp paper towels, place them in zip lock plastic bag and wait 7 days. They should germinate in 5 to 10 days. I will write an Instructable for the test germination process later.
Please visit my very active gardening blog at the Rusted Vegetable Garden.