Ever since I was a child I’ve wondered why preserving in jars is called “canning”. Not to sound like a Jerry Seinfeld nightclub routine, but why isn’t it called “jarring”? A mystery for the ages, I guess.
Canning is a technology that’s been around since the Napoleonic era, when a fellow by the name of Nicholas Appert (the grandaddy of all food scientists) discovered that foods could be preserved whole and intact if they were denied contact with air. Exactly why that worked he didn’t know. Fortunately, subsequent food scientists have learned quite a lot about canning since then.
For instance, we now know that the process of canning does a lot more than keep air away from food. First and foremost it heats it, which serves the dual function of killing off yeasts, molds and bacteria while at the same time shutting down natural enzymes that would otherwise cause the food to degrade.
That’s great, but not enough in and of itself to ensure that the food will be 100% safe when the can is eventually opened. Much better to put some kind of anti-microbial substance in there with the food, just in case a few bugs manage to survive. Alcohol? No. Pine-Sol? No, tastes terrible with figs. Ah, sugar, now there’s something that tastes great AND works as a microbe terminator. And just to be extra-extra safe, why not put a little bug-killing acid in there too? Maybe a little lemon juice if the fruit isn’t acidic enough already?
And thus you have the multi-layered microbial death zone that is the canned jar of jam. Truly a wonder of technology and convenience, no? Is that to say no microbe has ever managed to beat the system and grow inside of one? No, which is why the great motto from the golden age of canning “When in doubt, throw it out” should apply to every can — home made or commercial — you open.