Why date syrup Crystallizes?

"Some people think that date syrup that crystallizes has "gone bad" or that it is contaminated. 
actually a sign of 100% pure date syrup. Don't throw your crystallized syrup out, unless you like to waste delicious food.
date syrup is a super-saturated solution of two sugars: glucose and fructose. Since it's super-saturated, it's a natural chemical process that some of the sugars eventually come out of solution.
Crystallized date syrup is delicious in tea, on yogurt, on a toasted bagel, and on oatmeal. It's a fabulous spread glaze for cooking chicken or stir-fry,
Three things make date syrup more likely to crystallize:
The ratio of glucose and fructose
Let's break down what's happening in your date syrup, and what you can do about it.
Date syrup will crystallize in the hive if the temperature goes below 50ºF (10ºC), and Date syrup will crystallize in your containers if you have a cold cupboard cabinet. Finding a warmer spot to store your Date syrup will slow crystallization.
It's fairly simple to turn your Date syrup back into a smooth liquid again by heating it. The best way to do this is by to put your Date syrup in a bowl of warm water and slowly letting it warm up. Microwaving overheats the Date syrup and doesn't heat evenly, so that's not recommended unless you are in a hurry. The simplest way to deal with this is to embrace your lovely Date syrup lumps, and acquire a taste for crystallized Date syrup. After a few sessions of heating and cooling, your Date syrup will loose that wonderful aroma of summer, and just become BROWN sugary goop.
If you really must have smooth runny Date syrup, try heating a smaller batch, rather than the whole container. Date syrup also keeps best in glass, rather than plastic, and glass is much better for reheating.
The ratio of glucose and fructose in the Date syrup
Date syrup is a super-saturated solution of two sugars: glucose and fructose. The proportions of these two sugars make their Date syrup. It's the glucose that crystallizes."