I know what you’re asking yourself this morning, because I woke up asking it too: why, if preserves are just made of fruit and sugar syrup, can’t you just mix a good thick simple syrup with some cooked fruit and be done with it? The answer is, because what you get via jam making isn’t just any ordinary syrup.
Regular (simple) syrups are made (simply) by heating a mixture of water and sugar until the sugar dissolves. They can be light or heavy, and are used for things like moistening cakes and sweetening drinks like southern sweet tea. The trouble with them is that they eventually re-crystallize, which is why a very dense simple syrup is also called rock candy syrup (and if you’re wondering why that is, try suspending a sugar-coated popsicle stick in a 2-1 sugar-to-water solution for a week…your kids will love the results).
The reason preserves don’t eventually make rock candy of their own is that they are composed of a very special kind of syrup known as invert sugar syrup. It’s what happens when a sugar solution is heated in the presence of an acid (like oh, say, citric acid). The sucrose molecules split in two, resulting in free fructose and glucose. Since neither of these two monosaccharides re-crystallize very easily once they’re separated, the syrup stays liquid.
The neat thing about invert sugar syrup is that it’s actually sweeter tasting than the table sugar from whence it came. The reason: because gram-for-gram fructose tastes about 20% sweeter on the tongue than sucrose.
You know, you’ve got a really active mind early in the morning. Let’s do this more often.