Home-brewed sour milk from store-bought milk – why you shouldn’t

Why does milk curdle in the first place?

This is due to the activity of microorganisms that got into it. Lactic acid bacteria consume lactose and release lactic acid, the pH drops, milk protein coagulates — the contents of the jar change in texture.

By the way, milk is an attractive substrate not only for lactic acid bacteria. And if other groups of microorganisms grow there, no one will forbid them from producing any metabolites they want, for example, toxins.

Therefore, for good safe sour milk you need exactly lactic acid bacteria!

How can lactic acid bacteria get there?

Option one — you have a cow. It’s all straightforward — lactic acid bacteria live on the surface of the animal’s skin that provides the milk, and they mostly get there during milking. It’s fair to add that this all happens nicely when the animal is healthy and its owners are not lazy to wash their hands and dishes properly.

Option two — you have a starter culture. Today there is a wide range to choose from; you can make yogurt or kefir to your taste. You simply add a powder that contains lactic acid bacteria to the milk and wait for it to sour. This, by the way, can be done not only with a starter culture but also with ready-made store-bought fermented dairy products. But about this — in the next posts.

And now we recall, why store-bought milk can last so long — it has undergone heat treatment. Lactic acid bacteria — gentle and vulnerable creatures — most of them will die already at 50-60°C. Not so for bacteria that can form spores and survive pasteurization — a kind of great flood on a local scale — if you built an ark — a liter of milk is yours!

So what happens when we try at home to make home-brewed sour milk from pasteurized milk? Lactic acid bacteria lie dead on their bellies, while their adventurous colleagues eagerly hatch from spores and multiply vigorously! And it’s good if they don’t produce toxins or carry antibiotic resistance genes!

If this milk is long-lasting, it will probably stand a bit longer. However, due to the microbial saturation of the air of your kitchen, the fridge, the dishes and yourselves, sooner or later something will fall in and germinate. Will it be exactly these useful and desirable lactic acid bacteria? There is a probability, of course, but, admit it, it’s not that high. Therefore, if you want to sour something yourself, it is worth using a starter culture.

Speaking of homemade milk — if you overheat it, then, of course, lactic acid bacteria will also die. So in that case you should also settle them there somehow — a starter culture, sour cream, or yogurt will be perfect.

If you’ve lost a bit of appetite for drinking such home-brewed stuff, let’s move on to pancakes.

Thermal processing of food has saved us from food poisoning for quite some time — disease-causing bacteria cannot withstand a meeting with a frying pan, as well as most of their temperature-sensitive life processes that have a protein nature. However, there are a number of thermostable toxins, such as thermostable enterotoxin of Escherichia coli or Salmonella, which cause diarrhea and gastroenteritis. Therefore, it is safer to throw such milk away than to play roulette. It’s more pleasant to win in gambling :)