At my house, I refridgerate the ketchup, once opened. In the winter, my cupboards are pretty cool (on an outside wall) but in summer, my kitchen gets pretty toasty-it's the heat that causes items to deteriorate. I don't leave bread out either for this reason. I suppose if your house has central ac, it would not fluctuate this way. Mine does, so I keep all the condiments in the fridge, and butter and bread too.