A friend asked me the other day if the tomato jam recipe I posted two weeks (or so) ago can be canned. The answer is yes, the recipe I put up is in fact intended for canning, and now that I’m back up and around I plan to do that very thing (maybe even today). But it’s a very good question, since one should never attempt to can any sort of foodstuff for which there isn’t a safe, exhaustively tested recipe. Of course the Bible for those is the Ball Company Blue Book. Or if you don’t feel like paying out any actual money, the Ball web site. Both are chock-a-block with simple recipes that won’t result in any little surprises like oh, say, botulism.
The reason I make a sole exception for this jam is because of what’s in it. Tomatoes by themselves are highly acidic, so much so that they can virtually be packed as they are in a boiling water canner. But then notice I said “virtually”, which isn’t nearly good enough where canning is concerned, and why every good canned tomato recipe I’ve ever seen employs either lemon juice or powdered citric acid to pull the pH level down to where no microbe can survive.
Great-grandma’s tomato jam has that, though the lethality of the extra acid pales in comparison to the microbial knock-out punch that all that extra sugar delivers. Though I haven’t weighed it precisely, my estimation is that the recipe, once it’s fully simmered, ends up containing as much sugar as tomato flesh by weight (pretty standard for a jam), which means bugs don’t have a prayer. Me, I pack it in half-pint jars and process it for 15 minutes in my boiling water canner. Of course the easiest of all preservation methods is simply to spoon your jam into nice thick baggies and freeze it. It won’t last as long (several months instead of a year), but it’s a true no-brainer. And remember, as my grandmother always said, it’s always better to err on the side of caution if something in your pantry — particularly a canned something — looks or smells dubious to you. When in doubt, throw it out!