Cook just the tomatoes or cook all the salsa the night before? Cooking just the tomatoes would be a waste of time since cooking all the ingredients together is what allows the flavors to blend before canning it. And if you had to re-cook them the next day after adding all the other ingredients then the tomatoes are going to be really mushy.

But cooking the salsa itself - all mixed together - is no problem if it is then kept refrigerated overnight and re-heated the next day before filling the jars.

Just make sure you are using a safe, tested and approved recipe since salsa is nothing to fool around with given it is low-acid vegetables.

Dave

PS: I am assuming you understand that the salt is optional anyway.

In addition to the salt being optional, you could cook everything else and add the salt while reheating prior to filling your jars.

In this case, you could also use regular table salt since the clarity of brine isn't an issue. It isn't normally recommended because it has anti-caking ingredients that can cause cloudiness, but salsa isn't transparent anyway.

In the future, you may want to freeze your tomatoes (just rinse and toss them in a ziploc bag) until you're ready to actually can them.

Deanna