I have occasionally received a few more McDonald’s sweet and sour sauce packets than I actually need, and so I’ve saved them to use later. However, I’ve discovered that the sauce, even in the completely sealed packages, gradually turns dark over time. I found one packet whose contents were almost black. What causes this? Is the old sauce still edible?
There’s air inside the sealed container to react and oxidize with. Even if there weren’t, it’s unlikely that McDonald’s hermetically seals its condiment packages; air can still get in eventually.