Simple syrup finds its home in any well-stocked bar because sometimes sugar doesn't dissolve easily enough. Simple syrup is traditionally made by dissolving white sugar into water on a stove and then cooling before use, but sometimes, in a pinch, people will shake superfine sugar with room temperature water until dissolved. The ratio of sugar to water varies from between one to one to two to one. If you're shaking superfine sugar, you're probably using a one to one ratio; personally, I prefer to use a two to one ratio because you can always just use less. But no matter how you make it, simple syrup has a frustrating tendency to separate (or worse, grow mold) after a while, usually about a week or a month.
Maybe you go through a roughly quarter of a liter bottle of simple syrup every week to a month, but I certainly don't generally use mine up. So how can you extend the shelf life instead of discarding and making a new batch? Conveniently, chemistry has the answer to this one. You simply invert the basic sugar, sucrose, into its two basic components: glucose and fructose. The term "inverted" comes from measuring the concentration of sugar syrup through a polarimeter: when plane polarized light is passed through pure sucrose solution rotates to the right, but when it is passed through a converted mixture of sucrose, fructose, and glucose it rotates from right to left.
The best part is that if you're already making simple syrup on the stove, it doesn't take much more effort to make inverted sugar syrup instead - just a little more time. Once you have simple syrup boiling on the stove top, just add a pinch of cream of tartar (or if you don't have any on hand, you can add a small amount of lemon juice or another acid) and let the mixture simmer for another 20 minutes. You'll have more than tripled the time you can leave the syrup in the refrigerator.
In addition to making normal inverted sugar syrup, I also made a lavender sugar syrup for cocktails and other drinks by adding dried lavender flowers along with the cream of tartar before simmering:
I then let the flowers sit with the syrup in the refrigerator for three days before straining. We haven't experimented too much with this flavored sugar syrup yet, but we have discovered that adding a little to either a glass of lemonade or a gin and tonic is a delicious decision.
Inverted sugar syrup
- 2 parts white granulated sugar
- 1 part water
- Pinch cream of tartar (alternatively, lemon juice or another acid)
- In a saucepan, combine sugar and water. Bring to a boil, stirring constantly, until the sugar has dissolved.
- Add a pinch of cream of tartar and stir completely into the boiling simple syrup. Turn down the heat to medium low and let simmer, stirring occasionally, for 20 minutes.
- Allow inverted sugar syrup to cool and store in a refrigerator.