This post lists the spoilage times for different simple syrups. You can use it to determine how long until simple syrup will spoil.
Simple syrup is never just that simple. Some people make it 1:1 sugar to water. Others make it 2:1, and call it "rich simple syrup."
One-to-one simple syrup is easy to make- put equal amounts sugar and water in a bottle and shake it up. No heat is necessary. For rich simple syrup if you shake and wait and shake and wait you can get it into solution without heat, but most people heat up the water first on the stove and the sugar dissolves almost instantly (but then you have to wait for it to cool before using). Either way, you need to plan for it.
So why would anyone bother with rich simple syrup? Because you can use less of it in a drink to get the same amount of sweetening, but more importantly it lasts longer before spoiling in your refrigerator.
To test this, I made up four syrups and decided to wait to see how long it was until they spoiled. For each ratio, I added a tablespoon of vodka, as this is another method of making syrup last longer before spoiling.
- 1:1 simple syrup
- 1:1 simple syrup plus one tablespoon vodka
- 2:1 rich simple syrup
- 2:1 rich simple syrup plus one tablespoon vodka
Then I put them all in the refrigerator and waited. Eventually, the syrup would become cloudy then that cloudiness would start to mold. I stopped the experiment when the cloudiness appeared.
- 1:1 simple syrup lasted One Month
- 1:1 simple syrup plus one tablespoon vodka lasted Three Months
- 2:1 rich simple syrup lasted Six Months
- 2:1 rich simple syrup plus one tablespoon vodka lasted more than six months
So depending on how fast you go through simple syrup you may want to adjust the syrup that you make. Of course, you'll have to go back and adjust all your drink recipes too.