Re: Which substances wil elevate the freezing point of water?

How to answer? To the best of my knowledge (and that of the colleagues 
that I have polled), there aren't any substances that can INCREASE the 
freezing point of water. This has to do with the molecular mechanism of 
the process of freezing point depression/boiling point elevation.

In essence, the freezing point curve is based on the vapour pressure - on 
the pressure/temperature relationship - for water. By including a 
substance, you "block" water molecules from escaping the surface, 
altering the triple point, and shifting both the boiling and freezing 
points at any constant pressure. Because this blocking is only dependent 
upon the presence of a substance and not on its nature, it is 
a "colligative" property. That is, it depends solely on the number of 
particles that a substance forms. To have water freeze at a higher level, 
there would have to be some mechanism for increasing the vapour pressure 
of water. But giving a "110%" is not a possibility!

So, what is happening in your refridgerator? Good question! It is 
possible that you are not generating ice crystals but crystals of 
something else - say, some fat or sugar crystallizing out of solution as 
you have modified the temperature and therefore, their solubility. Or it 
could have something to do with differential cold spots in your fridge 
that are taking the temperature below zero. Or that there is something 
contained in your mixtures that is very volatile, and in evaporating 
within your fridge, thereby producing a local cooling effect. But I don't 
know how you could be getting ice crystals. And any of these would likely 
be a "one off" and not a continuing occurrence.

Sorry that this is not much of an answer. It is certainly an interesting 
phenomenon!

ADMIN NOTE:
I had a similar problem with fruit juice in my fridge freezing.  My fridge has
the freezer part inside the fridge, at the top,  and I kept the juice on the top
shelf.  I found that if I turned down the thermostat on the fridge a bit,  the
problem went away - it might just be "leakage" from the freezer.