For future reference - we keep grated cheese in the freezer. To use it we take the bag out of the freezer, take out what I think I will use and put the bag right back in the freezer. if it thaws, be careful when you re-freeze it to take the bag out and break it up before it freezes too solidly again. Re-freezing cheese is OK, the problem with cheese going bad is when it either goes dry and hard (when it becomes fondue fodder) or it goes mouldy. The bacteria in bad cheese are different ones to what you get in other bad food, especially in bad meat. Cheese is a lot more forgiving. Unless the mozzarella was at some stage left out at room temperature or stored uncovered or unwrapped (and therefore contaminated) Thanksgiving should not be too old for mozzarella. Unless it had gone mouldy.
There might have been something else he ate that was old and more rotten.
Marg
