Why did my ginger simple syrup develop such a disgusting consistency? I made a ginger simple syrup. I took a large amount of ginger, simmered it in water to cover for an hour, drained it (reserving the water), and repeated the process with fresh water. I did this three times. I took the reserved ginger water added a bit of sugar and reduced to maybe 1/3rd. Let it cool and stuck it in the fridge. It was cloudy and clearly had some fine ginger particulate floating around in it. It was very strong and tasted great.

I used it for a couple of weeks to make ginger based drinks, and then it got stuck behind something in the fridge to be rediscovered this morning. I made it 43 days ago, and it's probably been untouched in the fridge for 28 days. I checked to see if it was still good and it smelled ok, however, it had the consistency of mucus. It was really, really disgusting. I did not taste it. My wife tried to throw it out but started gagging as it oozed out of the jar. Naturally, I got a camera (unfortunately it's acting up and I can't upload the photos, hopefully they'll follow). 

What on earth caused this to happen?
My guess is that: 

 1) The syrup wasn't acdic enough 


and  

 2) The sugar concentration wasn't high enough.


If the sugar concentration is high enough, the sugar so-to-speak draws the water out of bacteria by osmosis thus killing them. If you don't like the syrup to be too sweet, try adding lemon juice.