How do things expire once you open them/ expose them to oxygen when they clearly had to be exposed to air before being sealed?

Question

Like milk goes bad a week or two after opening it but if you don’t open it, it will stay good until the expiration date? Like yogurt, sour cream, shredded cheese. All those things. I’m confused

In: Other

Answer 1

As others have mentioned during the packaging process they have the ability to remove all oxygen from the packaging which will far lengthen the shelf life of the item until it’s opened.

My buddy works in agricultural insurance and recently toured a new state of the art potato processing plant. Once the potatoes arrive they are cleaned and then they enter the massive building as whole potatoes, the entire building is air tight with no oxygen or light inside, the entire process is automated, first they are skinned, then cut into specific shapes/sized, dried (a few other steps in the process as well I’m sure), packaged in air tight wrap and boxed, all of which is done in a sterile environment without any light or oxygen, this drastically increases how they can last in their packaging. After this they will be shipped in either fridge or freezer trucks to distribution.

So for this example they actually haven’t been exposed to any oxygen whatsoever since they were cut, and uncut/fresh they naturally preserve for a pretty long period..