Why are shelf stable food items (like sauces, broths, etc) recommend to be used within a few days after opening? Do they actually go bad?

Question

I tend to keep condiments and things of that nature for a very long time in my fridge even though most Google searches say use within 3-5 days after opening. How can a sauce or can of broth or any other shelf stable thing last for months, if not longer, in my pantry, but if I open to use it for a few seconds and put it in my fridge it’s supposed to be used with if a few days? I’m talking anything from pickles to mustard to broth. All of those items seem perfectly fine in the fridge even after weeks or sometimes months.

In: Other

Answer 1

They do go bad because generally products like those come in sealed containers meaning that they aren’t exposed to the surrounding environment(microbes) and the factory probsbly also sterilizes them(boil in high heat). When you open them they are suddenly exposed to an environment filled with microorganisms that feed and grow on the food. Salty, Acidic environments prevent growth