Select a jalapeno plant that you want to save the seeds from. Choose a plant that is healthy and growing vigorously with the best tasting peppers of all the plants you have. Avoid any plants that seem sickly or have signs of disease or pests.
Cut the pepper from the plant when it has ripened fully. A fully ripened jalapeno will have turned from waxy green to red and be slightly shriveled and wrinkled.
Slice the ripe jalapeno pepper lengthwise, splitting it into two pieces.
Scrape out the seeds and lay them out in a single layer on a paper towel. Place the paper towel in a warm, dry place, away from bright light for two to three days so the seeds can dry.
Label an envelope with the variety of jalapeno seed and the date.
Put a silica gel packet in the jar. These are the little packets you find in new shoes or jacket pockets labeled "Do not eat." You can buy them at craft stores. Silica gel absorbs moisture in the air and will keep the seeds dry.
Put the labeled envelope of seeds into the jar with the silica gel and seal it up. The seeds will keep for planting in the next season. Multiple types of seeds can be kept in different envelopes inside the same jar. Store the jar in the refrigerator or other cool, dark place between 32 and 41 degrees Fahrenheit.