re: Freezing salsa

If you can salsa, you have to worry about botulism, it would never be safe to thicken it before freezing. Plus, the acid level is so critical when canning it, too.
However, frozen, it is fine. You don't have to worry if you are freezing it.

The Clear Jel is stable, it doesn't break down like regular cornstarch will. That is what the commercial industry uses, modified food starch, which can be Clear Jel. They have some other products they use, too, but Clear Jel is one of them and the one available to homecanners for canning pie fillings.