Zsiadłe Mleko

Soured Milk (Fermented, Cultured Milk)

” Through natural fermentation, fresh raw milk undergoes a transformative process, guided by the bacteria — resulting in a curd-like texture that’s simply irresistible.”

How to pronounce it?
zshiadleh mlekoh
‘Play’ to hear:

Soured Milk in a glass

Soured Milk is a light tart beverage – a little bit like yoghurt, but better! Traditionally, it was simply fresh raw milk that was kept in a warm place for a day – often by a kitchen stove. 

Milk acidifies naturally with time, thanks to the bacteria that are already there. These cultures would slowly “eat” the lactose away. With time, they multiply throughout – acidifying the milk by releasing lactic acid. Eventually, the milk sets and forms a curd.

For the full list of ingredients & detailed instructions, please see the recipe card at the end of this post. But before you scroll, there’s important stuff to know below.

I wasn’t sure if it is not too trivial to talk about something as simple as Soured Milk, but after all, it’s a staple of Polish cuisine (perhaps a bit forgotten, but still). 

Soured Milk is a great base for many summery dishes, it works great in baking too. Plus, there wouldn’t be ‘Twaróg’ (Polish-style farmer’s cheese) without it. Give it a go, it’s easy to make at home.

Do you need any special ingredients to make Soured Milk?

You’ll need one of the following:

  • Raw Milk (unpasteurised, unsterilized),
  • A combo of regular, pasteurized whole milk, together with sour cream.

Raw Milk: Souring the milk is a piece of cake if we can get it fresh. Raw, unpasteurized, unsterilized – basically straight from the cow’s teat. 

Milk cans stored outdoors

🇵🇱 In Poland, raw milk is sold at farmer’s markets, mlekomats (fresh milk vending machines) or you can order it online (e.g. from Rano Zebrano, Lokalny Rolnik)

🇺🇸 Getting raw milk in the US can be a bit trickier. I hear that selling raw milk is illegal in some states. If you’re a lucky cow owner – problem solved. If you have a farm nearby – great, here’s a Raw Milk finder for your reference.

🇬🇧 In the UK, I used to buy raw milk at the farmer’s market. A quick Google search tells me that some farms offer raw milk directly in their farm stores (or with delivery). Overall, it seems selling raw milk in the EU is totally legal.

Fresh Pasteurized Milk and Sour Cream: The trick here is to acidify the regular, pasteurized milk with some friendly bacteria. That can be done with a spoonful of soured milk from before, but who has that on hand? Instead, an addition of a regular sour cream works just as well. 

Fresh milk in bottles

When buying milk and cream, it’s worth reading the label. The list of ingredients should be as short as possible. Get the “organic” or “bio” products if you can, without any artificial additives or preservatives.

Important note: a shelf-stable UHT (Ultra-Pasteurized) milk won’t work at all. The milk will turn bitter. 

How should you serve this Soured Milk?

In Polish cuisine it’s common to serve a glass of cold Soured Milk alongside some young potatoes (baked or boiled), lightly sprinkled with chopped chives or dill.

They’re served together with eggs on the side – sunny side up. It’s a great lunch for a hot, summer day.

Can you make this Soured Milk another way?

  • Some recipes mention acidifying the milk with vinegar or lemon juice – but by doing so, the beverage won’t be cultured. We would be losing out on all the beneficial probiotics. And secondly, I find that there’s a difference in flavour and texture. Subtle hint: fermented milk is sooo much better!
  • If you can get cultured buttercream, you can use it instead of (or in addition to) sour cream.

What dishes can you make with Soured Milk?

Soured Milk can be used in cakes, pancakes, scones, muffins, cookies and other baked goods. Whenever you see milk, yoghurt or sour cream mentioned in a recipe – it can be substituted for Soured Milk. 

But there is more. Many Polish recipes use Soured Milk to make various ‘Chłodnik’ soups (cold soups).

It’s the key ingredient to make ‘Twaróg’ – a Polish-style farmer’s cheese. And ‘Twaróg’ goes everywhere: as a Pierogi filling, as a Crêpe filling, into ‘Leniwe’ dumplings, and crucially – into a Polish-style cheesecake.

What diets is Soured Milk suitable for?

Soured Milk is meat-free, therefore suitable for vegetarians. 

It’s also a probiotic superfood, supporting your digestive health. Try it – your gut bacteria will be over the moon. More on the health benefits of Soured Milk here.

How long can you keep this Soured Milk in the fridge?

Once the milk has soured, keep it refrigerated and consume it within 2 to 3 days.

Can I freeze Soured Milk?

No, I wouldn’t recommend freezing it. It turns grainy, fat separates from the liquid, the texture becomes uneven.

FAQ & Troubleshooting

🤔 What are substitutes for Soured Milk?

The best substitutes for soured milk are: buttermilk, sour cream or natural yoghurt (regular or Greek-style). They work well when cooking and baking.

🤔 How do you know that Soured Milk is off?

Have a taste – if it tastes bitter, that means it has spoilt. That happens sometimes, usually when:

  • The temperature during fermentation was too low. If we want the bacteria to transform our milk into a delicious beverage, it’s best to keep it souring at room temperature.
  • The milk (or a part of it) was in fact UHT (Ultra-Pasteurized) milk. Read the labels carefully – the ingredients list should be as short and natural as possible. Get the “organic” or “bio” type if you can, without artificial additives or preservatives.
A glass of Soured Milk beside a milk can
Yield: 1

Soured Milk (Fermented, Cultured Milk)

Soured Milk in a glass

Great for your gut health, homemade Soured Milk is THE beverage for a hot, summer day.

Here's a rule of thumb: You need 1 heaped teaspoon of sour cream per 1 cup of milk.

P.S. If you're using raw milk, there's no need for sour cream at all.

Prep Time 5 minutes
Cook Time 3 minutes
Additional Time 1 day
Total Time 1 day 8 minutes


  • 1 cup (250 ml) whole milk, pasteurized
  • 1 tsp sour cream, natural, cultured


  1. Heat up the milk to a warm temperature (it shouldn't be hot, just slightly warm). If you’re using raw milk and a cream forms on top - you can remove it.
  2. When using raw milk, no sour cream is needed. Just proceed to Step 5.
  3. When using pasteurized milk from a store, add 1 heaped teaspoon of sour cream (or more) per 1 cup of milk. For larger quantities, just use the same ratio. In general, there is no need to measure the ingredients exactly, just eye-ball it. 
  4. Mix milk and sour cream together with a fork. 
  5. Pour the milk mixture into a container of your choice. If you’re aiming for more liquid soured milk, pour it into a larger container - for example a large jar or a bowl. Personally, I prefer a firmer (almost solid) texture, so I’m pouring it into individual glasses. 
  6. Cover the container (that’s optional). Some people leave the container uncovered, some cover it with a cheesecloth - mainly to keep the insects away. I used a piece of a muslin square just to be safe.
  7. Leave in a warm place, for example - on the kitchen counter. Don’t stir it, don’t poke it, just let it be. 
  8. The fermentation process can anywhere from a few hours, up to 2 days. It depends on the temperature - if you live in a warmer climate, it should be ready within a day.
  9. Observe the milk. Once it has curdled, the consistency turns jelly-like and the flavour becomes pleasantly sour - it’s done.
  10. Refrigerate the beverage and consume within 2 days.


  • There is no need to measure the ingredients exactly, just eye-ball it.
  • Reminder: a shelf-stable UHT (Ultra-Pasteurized) milk won’t work at all.
  • Other Polish names for ‘Zsiadłe Mleko’ are: Skwaszone Mleko, Kwaśne Mleko, Silesians call it “Kiszka”
  • Nutrition Information:



    Serving Size:


    Amount Per Serving: Calories: 134Total Fat: 6gSaturated Fat: 3gTrans Fat: 0gUnsaturated Fat: 2gCholesterol: 22mgSodium: 129mgCarbohydrates: 12gFiber: 0gSugar: 0gProtein: 9g

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    Recipe Information

    Filed under:

    Alternative traditional/regional names:
    Skwaszone Mleko, Kwaśne Mleko, Kiszka (Silesian term), Ukwaszone Mleko
    Also known / Misspelt internationally as:
    Lacto-fermented Milk, Cultured Milk

    Tested by:

    First published on:

    Recipe by / Adapted from:

    Story by:

    Bibliography / References:

    Test Kitchen‘s recipes come from diverse Polish publications, authored by chefs, home cooks, recipe developers, and bulletin subscribers.

    Tested with pleasure in Warsaw, Poland, we offer an honest review of each recipe alongside additional guidance, cooking tips and serving suggestions.

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