Refridgerate after opening...why?

I have found a few no refrigerated foods that ask us to fridge it after opening. Why? I figure its got something with the opening (hence…after opening. Smart man I is.) but why? Is it the preservatives (and I believe it mostly the heavily chemical stuff that asks this) or what? Is the air waiting for something like this to degrade it and the deep cold protect our dips from disappearing? WHY WHY WHY?

You got to thank Pasteur for this. He demonstrated that there’s a lot of microscopic organisms in the air. Once you open that can or jar, bacteria and such land on it and start feasting. If you don’t refrigerate, then the food becomes a mass of bacterium that will make you sick. But that’s just nature’s way of recycling. If there weren’t any bacteria around dead stuff would lay around for ever.

dammit…I thought aging the mayo in the cupboard a few weeks would made it taste better

It’s also worth noting that refrigeration doesn’t stop the bacteria; it just slows them down. Eventually stuff in the fridge will go off (at varying rates).

Uh, actually, you can age that mayo if you feel like; it’s just not going to improve the flavor any. Or so says Ann Landers, anyway. Of course, she’s pretty well known around these parts for spreading ULs and other falsehoods in her column, but for once it looks like she actually did her homework:

(emphasis mine)

Further confirmation, of sorts, comes from the Hellmann’s Best Foods FAQ, which remarkably, I’ve posted a link to before:

Notice the conspicuous absence of any warnings about disease or illness as a reason to keep your mayo in the fridge.

(For some reason the Hellmann’s link looked really screwed up in preview, so here it is: )