Selecting Tomato Seeds for Saving and Starting the Process
Seeds from many plants can be saved simply by collecting them as they dry. Tomatoes take a bit more work. Tomato seeds are enclosed in a gel-like sack that contains growth inhibitors, which prevent the seeds from sprouting inside the tomato. The best way to remove this gel covering is to allow the fruits to rot and ferment. In nature, this happens when the fruit falls off the plant. For seed savers, we're going to speed up the process.
The first step is to choose your best-looking tomatoes. You want to save seed from the finest fruit, so that next year's plant will have good genes. Remember you should only save seed from open-pollinated (OP) tomatoes. That includes all the heirlooms.
To start the process, slice the fruit in half so that the stem end is on one side and the blossom end on the other. This will expose the seed cavities better than if you sliced through the stem end.
In some paste and smaller tomatoes, the seeds are so concentrated in the cavity that you can scoop them out and still be able to use the flesh of the tomato for cooking. Many slicing tomatoes will require scooping out all of the flesh with the seeds. Whichever the case, scoop the seeds into a clean bowl or jar.
Fermenting the Seeds Improves Germination
If there is not enough liquid from the tomato pulp for the seeds to float in, add up to a cup of water to help separate the seeds from the pulp. Then set the bowl or jar of tomato seeds and pulp in a warm, out of the way spot. You will need to allow 2 - 4 days for the fermentation to take place. As it does so, the mixture is going to begin to smell awful, so store the bowl where you won't pass by it frequently.
If you have glass canning jars available, they make a good container for fermenting tomato seeds. The extra space at the top of the jar controls some of the odor and the clear sides let you keep tabs on what is happening. Covering the top of the jar with cheesecloth or paper towel will keep fruit flies out and also diminish the spread of the unpleasant odor.
Remember to label each variety!
Fermentation is Complete
What you eventually want to see is a layer of mold on top of your seeds & pulp. The process is done when bubbles start rising from the mixture or when the entire layer of tomato pulp is covered with mold. Don't leave the seeds fermenting past this stage or they may begin to germinate.
Checking the Seeds in the Jar
It is harder to see the layer of mold through the glass jar, but you can generally tell the fermentation is complete when the seeds settle to the bottom of the jar in a watery liquid and the thicker pulp and mold sit on top of them.
Getting the Tomato Seeds Ready to Save
Finally, you can remove and dispose of the mold covering. Lifting it before rinsing the seeds will make rinsing easier, but it's not necessary. You can add some water to the jar or bowl and stir or shake vigorously. The good seeds will settle to the bottom, allowing you to drain off the excess first.
Cleaning Your Fermented Tomato Seeds
Strain the seed mixture into a colander and rinse the seeds well under running water. Try to remove any remaining pulp bits and mold, so that only clean seeds remain.
Drying Tomato Seeds
Spread the seeds onto either a paper plate or glass dish, to dry. Don't use paper or paper towels or the seeds will stick to them and be difficult to remove. Set them in a warm, dry spot and allow to dry completely. Shake them on the plate daily to make sure they don't clump and that they dry evenly. Don't try to speed the process by using heat or you might destroy the seed.
Storing and Saving Tomato Seeds
Once the seeds are thoroughly dry, you can store them in an airtight container, in a cool, dry place. The envelope shown here will be placed in a canning jar. Remember to label and date your seeds!