I'm trying to determine the source of a couple of mornings of extra time in the bathroom (feel free to read between the lines). My food has been my usual mostly Paleo diet, which usually includes a few frozen berries with a few spoonfuls of coconut milk before bed. It usally takes me about a week to get through a can of coconut milk. I keep the milk in a sealed Ziploc container in the fridge. I notice it gets a little less sweet toward the end of the week, but I am wondering if it sours like dairy milk and thus may lead to increased loose bowels. Other than the extra time on the john, I feel great so don't think I have a bug.
Coconut milk definitely goes sour after a few days. Often you can see the fats separate and/or a rancid smell. Sometimes the milk even gets a bluish hue. A week is pushing it in my opinion. Just smell it and taste it first before using.
I'm not sure if coconut milk will spoil, but I usually use mine up in a few days. You might try putting it in the freezer and see if that helps. You would have to take it out a little bit before you used it though.