My mother uses (and my grandmothers used to use) sour milk in the baking of homemade bread. This was generally whole raw milk that had soured.

I'm not so lucky as to be able to get whole raw milk from a source I trust any more but occasionally a carton escapes the thirsty horde at home and goes past its expiration date. If it's only a day or so gone then I'll use it as normal given that I exercise a healthy degree of scepticism anyway about BB dates but if it's any longer then my idea would be that I'd use it in a bread recipe.

To clarify: the carton is unopened and has been refrigerated since purchase. It is not UHT milk as that's relatively rare here with HTST (72C for 15 seconds) pasteurisation the norm (probably owing to the relatively low ambient temperatures here)

The question is how long after the expiry date is it safe to use milk in this manner?

  • Downvoter, care to comment?
    – noonand
    Commented May 2, 2016 at 14:23
  • 2
    Maybe someone didn't like the assumption that sour milk is safe at all? It's hard to tell whether it's safely soured or unsafely spoiled.
    – Cascabel
    Commented May 2, 2016 at 15:42
  • If you really want some tasty sour milk, just drop some absorbic acid in a glass or what ever amount your going to use, A pinch in a glass, ~1/8-1/4 tsp per qt. The more you add the more sour the taste.
    – Jerryf
    Commented Nov 19, 2016 at 10:12

2 Answers 2


I'm not so lucky as to be able to get whole raw milk…

Wait, then there's a flaw in your premise. Check the label. Any milk treated using high-heat processes like UHT, pasteurization or ultra-pasteurized milk doesn't sour like it used to in your grandmother's days; it spoils… goes rotten.

Spoiled milk is not the same as soured milk.

The ultra-pasturized milk sold in the supermarket is essentially a dead product, with little to no live bacteria. When it goes bad, it rots and should be thrown out (or you can make plastic with it). Modern industrial pasteurization kills the “good” bacteria that once made sour milk a wonderful thing for cooking and making bread and cheese.

Substituting "Sour Milk"

If you have a recipe calling for sour milk, put a teaspoon of vinegar in a cup of fresh milk and let it sit for a few minutes. That's about the best you can do if you do not have access to raw milk.

  • 2
    I don't think you even have to say "ultra" here; as far as I know, any pasteurization at all means it'll at least potentially spoil rather than safely souring. And even with raw milk it's not a guarantee. It's much more likely safe, but still, even with most people in the US drinking pasteurized milk, there are around ten outbreaks a year due to raw milk with "bad" bacteria in it. And those people were probably just drinking it fresh. If you let it go sour and your milk was contaminated, you could get much more severe foodborne illness. Maybe not a huge risk, but not really safe either.
    – Cascabel
    Commented May 6, 2016 at 15:22
  • 1
    @Jefromi Yes, you are correct. Low-heat pasteurization methods aren't in wide-spread use that supposedly retain more of the healthy properties that high-heat kills. Nothing guarantees against bacterial contamination, but I was writing more on the defensive side in case someone wanted to call out that not all pasteurization creates a near-aseptic product. Commented May 6, 2016 at 15:33
  • The clincher here for me is the phrase "spoiled milk is not the same as sour milk". Here in Ireland UHT is relatively rare with HTST (72C for 15 seconds) pasteurisation the norm (probably owing to the relatively low ambient temperatures here)
    – noonand
    Commented May 7, 2016 at 10:57

It's not a specific date, as there are just too many variables -- what temperature it's been stored at, and how many days since the seal has been broken are likely more significant.

Growing up, my mom would use it for pancakes and baking once it started to smell a little bit off, but would dispose of it when it started to curdle (separate & get chunky).


As for the dates -- they're often not 'expiration', but dates to get stores to rotate their stock. (and if the stores or customers trash the product, the manufacturer makes more money, so doesn't care). They're dates like 'sell by' or 'best by' and such like that. See :

And there's usually a few news reports at any given time talking about how they're kinda crap (except for infant formula). Today's is from Canada.

  • 1
    Agreed. With milk, your nose knows. With whole milk I get AT LEAST a week after the "sell by" date. 2% doesn't last as long. Commented May 2, 2016 at 17:16
  • 1
    The biggest variable is what it's been contaminated with after pasteurization, in particular after opening. Very often it will never turn into safe soured milk: it'll go from not sour to spoiled. It may still last well past the expiration date, for sure, but without being sour.
    – Cascabel
    Commented May 7, 2016 at 0:41
  • FWIW the dates on milk cartons in Ireland are specifically "use by" dates (with the usual caveat that once opened you use it within 3 days). The original question refers to an unopened carton that's been refrigerated since purchase.
    – noonand
    Commented May 7, 2016 at 11:02
  • @ChrisBergin Re the "nose knows", I agree wholeheartedly but didn't express it as succinctly when I said that I exercise a healthy degree of scepticism anyway about BB dates.
    – noonand
    Commented May 7, 2016 at 11:08

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