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

If you find your milk going bad/shredded cheese going moldy/bad before you consume all of it, try Ultra High Pasteurized (uht) milk from a warehouse store and if the shredded cheese is used in a cooked dish, freeze the unused portion, the texture will be off when defrosted but the flavor is identical in cooked dishes.