What happens if you add pure food grade lactic acid that is free of bacteria to fresh pasteurized milk? What chemical reactions would take place? What does it taste like straight after mixing and a short time later (not so much later that bacteria could multiply and sour the milk) Does it smell and taste like sour milk? Or like yogurt?

I'm asking the question as part of my amateur research into sour milk. I am not especially interested in yogurt. I am especially interested in how similar or not fresh milk with lactic acid added is to slightly sour (revolting smell and taste) milk.

Is fresh milk with lactic acid added anything like sour milk in taste or smell?

  • $\begingroup$ The sour smell of yogurt, cheese, sweaty socks,.... comes from acetic acid and many other fermentation byproducts. Lactic acid is basically free from scent, tastes simply sour. $\endgroup$
    – Poutnik
    Apr 29 '21 at 21:14
  • $\begingroup$ What is the down voting for? $\endgroup$ Apr 30 '21 at 20:55
  • $\begingroup$ I did not vote and do not know why others voted, but maybe a reason is to be found in the old Latin expression: de gustibus non disputandum est. People have no way of knowing how other people perceive particular smells and tastes. Just my two cents. $\endgroup$
    – Ed V
    Apr 30 '21 at 22:31
  • $\begingroup$ @EdV One should not argue about matters of taste. One of my favorite maxims. But I asked what chemical reactions would take place, and how similar to sour milk the taste of the mixture would be. The disparaging remarks about sour milk were just for clarity and to make the text more readable. Anyway, thanks for hazarding a guess. $\endgroup$ Apr 30 '21 at 23:37
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    $\begingroup$ I find the question interesting but it seems mostly about the taste of a particular food. You might really want to give seasoned advice SE a try: cooking.stackexchange.com/questions/100389/… $\endgroup$
    – Buck Thorn
    May 1 '21 at 8:10

Likely, you'd get a yogurt-like mixture, and, eventually, cottage cheese: "Cheesemakers create cottage cheese by heating... milk, then mixing it with an acid -— which could be lactic acid-producing bacteria cultures or an acid like rennet, vinegar, or lemon juice. This acid causes the curds and whey to separate."

There are differences between just adding lactic acid and letting lactic-acid producing bacteria do the work.

  • The bacteria consume some of the milk sugars, reducing sweetness.
  • The bacteria have other waste products, which produce accustomed flavors of yogurt.

As for skipping the pre-heating step, I don't think it will greatly change flavor, but it might allow growth of undesirable microbes and it would likely increase the time for the curds to coagulate.

It seems that you'd need to experiment to see if you like the taste of the product.

  • $\begingroup$ The vile smell and taste of sour milk is surely unmistakable. I don't AFAIK have access to lactic acid, otherwise of course I would try the experiment.Interesting point about the bacteria consuming sugar and reducing sweetness that way. I hadn't thought of that. On the other hand, adding sugar to sour milk does not make it any less revolting. $\endgroup$ Apr 30 '21 at 21:01
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    $\begingroup$ It depends on which bacteria colonize the milk first... The "vile smell" is likely from butyric-acid producing bacteria, which may even be desirable in some aged cheeses. If you're lucky, though, the a more pleasant lactobacillus may make yogurt or buttermilk. Don't sour on making your own cheese! $\endgroup$ Apr 30 '21 at 21:33
  • $\begingroup$ Which bacteria and which aged cheeses? I'm surprised to hear that anyone would want to eat cheese that tastes of sour milk. I'm focused on sour milk right now, but making my own cheese is interesting, especially if I could use sour milk to do it. $\endgroup$ Apr 30 '21 at 23:32

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