I got a question last night as to whether cake syrup qualifies as an invert sugar. Talk about an early Christmas gift, that’s my favorite question! The answer is, in this case, yes. Not every sugar syrup is an “invert sugar” of course. Some are simply solutions of melted sugar in water (these will eventually crystallize again if left to sit). But the recipe that I put up yesterday qualifies as an invert sugar because it contains acid (orange juice), and sucrose + acid + heat = invert sugar. Why? Because heat and acid go to work on sucrose molecules (double-sugars made from one molecule each of glucose and fructose), breaking them into their component parts (a process known as hydrolysis). The result is a solution made up of about 37% glucose, 37% fructose and 25% sucrose.
What’s the difference? For one, it won’t crystallize, since free glucose and fructose tend not to form crystals (and keep the remaining sucrose from doing it). But invert syrup is also sweeter than a simple sugar syrup, since fructose tastes about 20% sweeter to our taste buds than regular table sugar. Also, it’s a better moisture retainer than simple syrup, which is of course a good thing for cake makers.