Is sour milk, soured milk, and milk that has gone sour, all the exact same thing? Related to this question: Is buttermilk another term for sour milk or some part of sour milk? and especially this answer to it: https://cooking.stackexchange.com/a/115571/93811 and two of the comments appended to that answer, specifically:

"Is soured milk the same as sour milk as in, 'I kept this milk in the fridge too long after opening, and now it is sour, although it was okay yesterday, and so I need to chuck it out and buy some more'. – Matthew Christopher Bartsh yesterday

@MatthewChristopherBartsh Not exactly. “Kept in the fridge and something grew” is the problem - you don’t know what grew. Way back before commercial milk production, there was a good(-ish) change that something desirable grew - souring meant “let stand, it’ll be thick by tomorrow” or it meant “add some of the existing product and let the microorganisms from that multiply and do their thing”. It’s too complicated for a comment to explain why exactly the former is less likely to work today than back in our (great...)grandparents’ time. – Stephie♦


1 Answer 1


Yes, it is the same. It refers to milk which has been left out until it has gone sour with whatever wild bacteria it has managed to catch, be they pathogenic, healthy, or neutral. It curdles a bit and changes in smell and taste.

If you find a person or author who makes a difference, then you have discovered either some regionally restricted distinction which is not widespread (maybe even restricted to that one author), or a too-literal translation from some other language.

Update, since you seem to be asking about the exact meaning of Stephie's comment. What she means is that back in the day, when milk went sour, the actual risks were lower than when today's milk goes sour. (not to speak of the perceived risks and of the implicit risks/reward calculations people make by gut feeling). The difference in her comment is not between "sour milk" and "soured milk", but between "milk that was freshly milked from a single healthy cow and left at room temperature until it went sour" and "commercially produced and processed milk which was distributed to me and left in the fridge until it went sour". There are no terms in the English language which make this distinction, both are called "sour milk" or "soured milk" - so the product is probabilistically different, but the words are not.

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    But, that doesn't make it exactly the same. Like sour cream vs cream that's gone sour - one was intentional & further pasteurised to prevent it going any further; the other was left in the fridge until something random grew in it.
    – Tetsujin
    Commented May 11, 2021 at 9:00
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    @Tetsujin I have never seen somebody make this distinction by using the word "sour" for milk. Milk which has had some culture added has a different name in English, depending on the culture/process: yogurt, buttermilk, kefir, etc. Other languages do use the term, that's why I mentioned the too-literal translation.
    – rumtscho
    Commented May 11, 2021 at 9:04
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    tbh, I've never seen "sour milk" for sale anywhere, but sour cream I can get in any supermarket.
    – Tetsujin
    Commented May 11, 2021 at 9:06
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    Yes, it was absolutely acceptable and common. In fact, my own grandparents' generation did it, and it was widespread. And if it was too-far-gone, it was "hidden" by using it as a baking ingredient instead. It is absolutely normal that tastes and attitudes towards food are part of culture and not absolute - you shouldn't use your own experience to predict other people's preferences and reactions to certain foods.
    – rumtscho
    Commented May 15, 2021 at 11:51
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    Rule of thumb: if it’s sour because it’s a carton of store-bought milk forgotten in the fridge, forget it. If it’s sour because it’s a batch of raw milk left at room temperature, it’s dubious. If you added the bacteria on purpose, enjoy!
    – Stephie
    Commented May 18, 2021 at 15:08

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