Yes, but you must add a substantial amount of acid to the mix in order to can it safely. Vegetables and other low-acid foods either have to be sealed in jars and sterilized in a pressure canner or have enough acid added to essentially pickle them, so that they can be sterilized in a simple boiling water bath.
Here’s one recipe; we’ve also included another recipe that has you freeze the salsa instead. The downside of either, of course, is that salsa is best when fresh, and either cooking or freezing will degrade the texture somewhat. But that's a small price to pay for being able to enjoy your homemade salsa through the dark months.
Cooked Tomato & Pepper Salsa
1-1/2 pounds sweet peppers 2 to 3 red or green chiles, seeded 1 large red onion 2 garlic cloves peeled 3 Tbsp olive or vegetable oil 3 Tbsp red wine vinegar or lemon juice 2 tsp salt 1 pound firm tomatoes, peeled, seeded, and coarsely chopped 3 Tbsp chopped cilantro or parsley
Coarsely chop the peppers and onion, then add them to the food processor along with the garlic, oil, vinegar or lemon juice, and salt. Process until finely chopped. Put the mixture and the tomatoes and herbs in a saucepan, bring to a boil, then simmer for five minutes. Pour the mixture into sterilized jars, and process in a boiling water bath for 20 minutes. Makes about a quart, and will keep for 6 months.
Frozen Tomato Salsa
2 Tbsp olive oil 1 medium onion, finely chopped 1-1/2 stalks of celery, minced 2 Tbsp serrano peppers, seeded and chopped 1 clove of garlic 4 medium tomatoes, seeded and quartered 2 Tbsp lime juice 1 tsp mild honey 1 tsp chopped fresh basil or 1/2 tsp dried 3 Tbsp chopped cilantro 1/4 tsp ground cumin 1/4 tsp chili powder
Heat the oil in a skillet and add the onions, celery, peppers, and garlic. Sauté until soft, about 5 minutes. Add the other ingredients, bring the mixture to a boil, cover and reduce the head, and simmer for 15 minutes. You should be able to pick out the tomato skins as the mixture cools. Ladle the salsa into two 1-cup freezer containers and let cool.
You can keep the salsa in the freezer for at least 6 months. Thaw it in the refrigerator before using.