Heirloom tomatoes are simply open-pollinated tomatoes that have the ability to be grown from seeds. If you have a passion for gardening or growing your own food, you can harvest the seeds from an heirloom tomato. Those seeds must then be prepared in order to save them until the following spring when it is time to get your garden ready for planting.
Rinse off several ripe heirloom tomatoes and slice them in half with a sharp kitchen knife. Dull knives won't cut through the tomato skin.
Squeeze the seeds from the tomato out into a glass jar. Pour water into the jar until it reaches at least 2 inches above the seeds.
Wait three to four days for white mold to begin growing on your seeds. When this happens, remove the mold, water and any seeds that were floating in the glass jar. You want to save the seeds that are still sitting at the bottom of the jar.
Place the remaining heirloom tomato seeds in a fine mesh strainer. Rinse them under cold, running water.
Set the rinsed seeds on a paper plate so that they are in a single layer. Wait three to four days for the seeds to completely dry.
Transfer your heirloom tomato seeds to an envelope. Label the envelope so that you know what type of seeds are inside. Store in a cool, dry place.