Info Thursday
Why Does Nutella Harden in the Refrigerator?

I was curious about this question, so I did some digging and found that palm oil, an ingredient in the US type of Nutella, hardens in a cold environment.

Sources:
http://www.nutellausa.com/ingredients.htm
http://www.americanpalmoil.com/publications/Guideline%20for%20Handling%20and%20Storage%20of%20Palm%20Oil%20Product.pdf
http://www.lonelyplanet.com/thorntree/thread.jspa?threadID=1753730
http://www.ehow.com/facts_5819492_palm-oil-biodiesel-disadvantages.html