How to determine if canning is safe? How can I tell if it is safe to can a particular homemade sauce? Is it just a function of pH and technique (pressure vs boiling water) or are there any other factors in play?

Specifically, I would like to can a tomato sauce that I use as a base for pasta dishes. I do not have an exact recipe but it's basically:


cook down loads of tomatoes until there's very little liquid left
whisk olive oil in to tomatoes
saute some garlic, anchovies, and red pepper flake
stir in to tomatoes


The tomatoes are obviously acidic, and I assume this intensifies as they cook down. Does adding the olive oil, garlic, or fish create issues though?
In regards to your particular tomato sauce. I don't think its acidic enough (a pH of 4.6 that is), and according to this page - the answer is no.  Even when canning fresh tomatoes or other tomato sauces you need to add some lemon juice.  Now you could try lowering the ph, but it would drastically change your recipe probably - whether or not you want to do this is up to you.

If you have a pressure canner, you likely can do it.

Generally, yes - it is a function of temperature and acidity. You need to either sterilize the food through temperature, or create an environment in which the bacteria won't grow - normally a higher acidity.  Pressure canners work by sterilizing, so recipes that are low in acid can still be canned.