I bought a bottle of pasteurized milk (not UHT) on Tuesday and accidentally left it out for two warm days. I went to discard it when I found it because of the curdling, but the smell was really pleasant, like fresh yoghurt or light kefir. I know the putrid smell of spoiled milk and this was definitely not it. If I didn't knew better, I'd try eating it as it is, it was a really nice smell.

I wanted to boil the milk for 30 minutes and use it for kefir but during boiling the curds separated even more and it turned into white cheese, which is fine as well. Is this cheese still safe to eat? I know that botulinum toxin gets neutralized after 10 minutes of boiling but what about other potential pathogens in milk? I'm really hung up on the fact that there was no unpleasant smell - can milk smell good and still be dangerous, even after boiling?

EDIT: this question was marked as a duplicate of Can adequate heating transform spoiled food into safe food?. The difference is that this question asks specifically about unopened, curdled pasteurized milk that doesn't have an off-smell and that was left out for only 2 days. This significantly limits the type of microbes and biological process that could be present in the milk and it's safety after cooking. The other question makes no differentiation between what appears to be naturally-made sour milk and rotten meats, neither does any of the answers to that question. I'll preemptively also add that Can pasteurized milk turn into yogurt by itself? is also not a duplicate, because it makes no mention of reboiling the milk to make it safe again.

Additionally, I'd like to mention that in my opinion this is an important question to ask and answer because online there are many resources that claim that slightly spoiled milk is safe for cooking, from potentially safe: in recipes that are heat-treated; to definitely unsafe: as a replacement for yoghurt, without heating. Naturally soured milk was also traditionally consumed and also spoiled on purpose in traditional recipes. Considering that this a potentially unsafe practice that is supported by tradition, I have a strong opinion that it deserves being answered.

I'll restate - this question asks about safety of seemingly safe (no smell) but soured milk after repasteurization. Any answer that doesn't address this specific question is not a duplicate.

  • I know that "food safety" is a term that gets used very loosely. On our site, it's defined very strictly: we only answer in line with official food safety regulations. The regulations don't make provisions for treating milk differently from other foods, so this is clearly a duplicate. For further detail see the tag wiki,cooking.stackexchange.com/tags/food-safety/info. If you wish to apply a different standard of "safe", you need to find a different source of information outside of our site.
    – rumtscho
    Commented Jul 7, 2023 at 17:15
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    Basically, boiling it won't make it safe: either it is already safe, i.e. you have successfully made aludttej "slept milk"; or you've grown some lovely toxins that'll just get concentrated by boiling. We can't tell you which scenario applies to you, so you'll have to make your own decision.
    – Marti
    Commented Jul 7, 2023 at 17:17