I'm no food technologist but squeeze an orange and put it in a glass, which is pure orange guice (100%?) and leave it on a table, and do the same with the 100% store bought one. The one from a bottle or cardboard box, not the "squeezed today" ones which are refrigerated. There will certainly be a difference, the freshly squeezed one will be stale, possibly ransid within a day. The bought one, not so sure... So there is obviously "something" else. Either preservative or some process done to the fruite.
Have you actually tried this? What did you find? Because I actually conducted something very similar to this experiment with someone else once, because they said the same thing as you just did and I was skeptical. We left the one we squeezed in the fridge for several days (I want to say almost a week, but it's been a few years so I don't remember exactly) and it was fine when we drank it after. We did cover the whole glass to avoid constant air exchange etc. (I didn't try doing it without that) but it was a fairly decent debunking as far as I was concerned.
Not intentionally, but generally yes, just by forgetting a glass. However, it also has not happened recently, I don't drink any kind of bought juice any more. I squeeze it myself.
Well next time you squeeze one, try this yourself intentionally. Fill a glass with orange juice, put some plastic wrap tightly over it, leave it in the fridge for a week (or however long you think is the average selling period for your local store), then try drinking it and seeing if it tastes rancid like you expect. Then ask yourself honestly if what you observed is significant support for the notion that the store-bought ones have preservatives or something.
I have done this repeatedly over the last few years (I drank a lot of freshly squeezed orange juice for a while and squeezed it in bulk) and I can therefore say with certainty that orange juice that is fresh will start tasting weird after 1-2 days in the fridge (kind of tingly, like it's fermented). This doesn't happen with fruit juice of any kind from a carton, to say nothing of the fact that orange juice from a carton is fairly disgusting.
How much air contact do you let your squeezed juice have while it's in the fridge? Also, what do the labels on your carton say? (Like ingredients, "from concentrate", "pasteurized", anything else potentially relevant?)
I've tried pasteurized and from concentrate. It should surprise nobody that those don't really grow things, but then I store both types in whatever carton they come in or that I decant them into (I had bottles for the squeezed orange juice). I kept neither completely open in the fridge, as that makes everything smell like orange juice and the orange juice itself taste like fridge.
If your question is merely why yours only lasts a couple days when mine lasted a week, it might've just been due to a difference in air contact or something, since in my case I think I pretty much filled a glass to the brim, put plastic wrap over it, and left it like that in the fridge for a week. I think my goal in that particular experiment was just to show orange juice doesn't inherently need special treatment to last that long.
But I thought the whole debate here is whether they're doing something to commercial juice that's different from what you get when you squeeze your own. In which case... shouldn't you be comparing home-squeezed vs. the store-bought ones that are not pasteurized or from concentrate? The ones that are claiming they're absolutely nothing but just squeezed orange juice? If the label already says it's been treated differently then there's nothing to investigate...
I will readily admit that I don't believe such a juice exists in any shops close to me. Anything that claims to be fresh is from concentrate, pasteurized or barely the juice that it claims to be (eg 90% apple juice, 7% the juice that you want, 3% unaccounted for).
Ah I see. It depends on where/which country you are I guess. As a couple examples, if you're somewhere with a Target, Simply Orange [1] claims to be pasteurized, whereas Tropicana does not [2], and neither is from concentrate. Although it's possible they both are pasteurized and the labeling isn't required... I don't know if it is.
However, if your next-best option is pasteurized juice, that sounds... just fine, if not even better? I mean I hope you're not finding pasteurization a horrifying Big Ag conspiracy of some sort. And pasteurization seems like a pretty plausible explanation of the difference you see compared to what you squeeze yourself... so then what's the huge worry?
Not to mention the taste.