Post #749410 by Limbo Lizard on Tue, Aug 18, 2015 11:16 AM

The reason one adds a little lemon or lime juice to hot-process, 'invert sugar' simple syrup is because the citric acid acts as a catalyst, assisting the heat in breaking apart the complex sucrose molecule into the simple sugars, glucose and fructose. But fruit juice contains other organic material - mold food! - in addition to the citric acid. I started using pure citric acid crystals, instead of fresh juice, in simple syrup, falernum, etc., and ceased having mold problems. For the same reason, if you want a hint of vanilla in your simple syrup, use the extract, not a vanilla bean.
I share Swanky's experience, that if you heat the mixture so that you convert enough sucrose to 'invert sugar', it is stable and mold-free, without refrigeration. A small bit of citric acid - not enough to change the taste - helps the process move more quickly and with less time heating, but is not essential.

P.S.: I'll ad a link to a previous post I made in another thread on this subject, which in turn, had a link to an informative post by a one-time-only poster, in yet another thread on the subject:
http://www.tikicentral.com/viewtopic.php?topic=36401&forum=10&vpost=530845

And, you might notice, Swanky has been educating about the "hows-and-whys" of creating invert sugar syrup for a good many years, now!

"The rum's the thing..."

[ Edited by: Limbo Lizard 2015-08-18 11:58 ]