Zakwas: Sour Rye Starter for Żurek (and Other Soups)

Zakwas Żytni na Żur, Żurek i Zalewajkę

Sour Rye Starter is the soul of Żurek, one of the most flavour-packed Polish soups. Even if you live thousands of miles away, it’s easy to recreate it at home.

All you need is good rye flour, water and…time. Just let the lacto-bacteria and wild yeast do their thing.

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.

If you’re familiar with sourdough bread baking, this recipe will sound familiar. In essence, making Rye ‘Zakwas’ starter is a very similar process. The key differences lie in proportions and an addition of garlic, but the principles stay the same. 

Once your Rye ‘Zakwas’ has fermented, try using it following these recipes:

  • Classic Żurek Soup
  • Żurek Wielkanocny (also known as ‘Polish Easter Soup’)

If you would like to learn more about flour ‘zakwas’ in Polish cuisine and what’s exactly going on inside the jar, here’s the full guide on Polish flour starters.

Do you need any special ingredients to make this Rye Starter?

There’s only one ingredient that might be trickier to source: wholemeal rye flour, ideally organic. This type of flour should be available in larger supermarkets and health stores.

It’s worth looking up your local flour miller online. They often offer their products directly – at competitive prices and much better quality.

🇺🇸 In the US: I’ve seen wholemeal rye flour available “in stock” on Walmart and Wholefoods websites. If you have trouble finding it in-store, you can get it off Amazon, for instance this Organic ‘Food to Live’ Rye Flour. (affiliate link)

This post contains affiliate links: Find out what that means.

🇬🇧 In the UK: Big supermarket chains (Tesco, Asda, Sainsbury’s etc.). Here’s a list of UK artisan millers, listed by region.

🇵🇱 In Poland, look out for ‘Mąka Żytnia Razowa 2000’. It’s available in larger supermarkets, health stores and online.

What dishes can you make with this Rye ‘Zakwas’?

Rye ‘Zakwas’ Starter is the magic ingredient behind an array of Polish soups, such as Żur, Żurek and Zalewajka. It’s also used to thicken the consistency of sauces and stews. 

Can you make this Rye ‘Zakwas’ another way?

Yes, if you’re a home baker. If you keep a rye sourdough starter alive, you can use it to kick-start our Zakwas. Just add some of it to the recipe (at the bottom of the post), and Zakwas will be ready faster – even in just 2 days!  

How do you know when this Rye Starter is ready?

Rye ‘Zakwas’ Starter needs 4-5 days to become ready. Properly fermented ‘Zakwas’ has a sharp, sour (yet pleasant) aroma. This smell reminds me of the leftover pickle juice (the fermented kind, not vinegary). If it turns bitter, that means something went wrong – check the FAQs below.

What diets is this Rye Starter suitable for?

Rye contains gluten, therefore the Rye ‘Zakwas’ is not suitable for gluten-free diets. I would recommend a Buckwheat-based Starter instead.

How long can you keep this Rye ‘Zakwas’ in the fridge?

Once Rye Starter has soured, it can be used straight away. Alternatively, pour it over into a jar, close the lid and store in the fridge for up to 2 weeks. 

Can I freeze this Rye ‘Zakwas’?

I don’t think you can, at least not with satisfying results. I couldn’t find any information about it online or in literature. But it’s common to freeze the end product – the soup. 

If you decide to freeze ‘Zakwas’ anyway, please let me know how it went. I’m curious what the result will be.

How do I reheat this Rye Starter?

There is no need to reheat it. Once added to the brewing soup, it will warm up naturally.

FAQ & Troubleshooting

Here you’ll find answers to the most common questions regarding Rye ‘Zakwas’ Starter. If you can’t find an answer to your question, please let me know.

🤔 Can you buy a ready-made Rye ‘Zakwas’ Starter?

In Poland ‘Zakwas’ for Żurek is sold in jars or bottles. It’s available in almost every store and in some bakeries. Make sure that the ingredients list is as short as possible: ideally just rye, water and garlic. If you have a Polish deli nearby, it’s worth asking if they have it in stock.

🤔 Flour sediment forms at the bottom of the jar. Should I discard it?

In short – no. To expand on that answer: it depends how thick you would like your soup to be.  

The more of that floury ‘mud’ you add to the soup, the thicker it will be. If you’re unsure how to proceed, add the clear part first. Then slowly start adding the floury part, one tablespoon at the time. Taste as you go. Is the soup sour enough? Is it thick enough? If not, keep on tinkering with it.

🤔 How much Rye Starter do I need for a soup?

The more ‘zakwas’ you add, the sourer the soup will be. For 1 litre (approx. 1 lq quart) of a ready Żurek:

  • You’ll need from 150 ml (10 tbsp) for a mildly sour flavour, 
  • up to 250 ml (1 cup) for a ‘properly’ sour soup. Or more, just taste and adjust.

🤔 It didn’t work! Zakwas is off / mouldy / bitter / smells funky…

Well, that happens sometimes. You have to remember that we’re letting the bacteria and yeast roam free, therefore the results aren’t 100% predictable. Here’s what you could try next time:

  • Try with different flour. A different brand perhaps. 
  • Make sure that nothing floats above the water level. 
  • Limit the ingredients to a minimum – flour, water and garlic is enough. Some recipes mention adding a piece of rye bread into the jar, but every time I do so, my ‘zakwas’ goes mouldy.
  • Make sure your jar is 100% clean.
  • Is your room warm enough? Cold temperatures aren’t starter-friendly.

A jar with rye 'zakwas' - a fermented flour starter for Polish Żurek soup
Fermented Rye Flour in a Jar, ready to be used in Polish Sour Rye Soup

Zakwas Żytni: Sour Rye Flour Starter for Żurek (Polish Sour Rye Soup)

Yield: 6-8
Prep Time: 10 minutes
Additional Time: 5 days
Total Time: 5 days 10 minutes

Sour Rye Flour Starter - or ‘Zakwas Żytni’ as we call it - is a tangy, lacto-fermented liquid. It’s used as a base for traditional Polish soups (such as Żur, Żurek and Zalewajka), but also to thicken stews and sauces. It’s easy to make: some flour, quite a bit of water and...tons of patience.

This recipe makes around 500ml (just over 2 cups) of Zakwas, that’s enough for around 2.5 litres (2.6 liquid quarts) of Żurek (that’s roughly 8 portions)

Ingredients

  • 7 tbsp (100g) Wholemeal Rye Flour
  • 2 1/4 cups (500ml) Water
  • 4 garlic cloves

Spices (optional, see the 'Notes' section):

  • 4 bay leaves
  • 5 all-spice berries
  • 5 back peppercorns
  • 1 tsp dry marjoram

Instructions

    1. At a later stage, you’ll need a cooled boiled water. I’m mentioning it now, so that the water has time to cool. If you have an activated carbon filter at home, you can use that filtered water instead.
    2. Prepare a 16 oz (500 ml) jar. We don’t want any bacteria in there, so it needs to get clean. There are two easy ways to sterilize a jar:

      In a microwave: pour some water into the jar, set it on the highest setting for 2 minutes. Normally, we would sterilize the lid in a pot of boiling water, but this time the lid won’t be necessary. Dry up the jar completely. 

      On the stove: Using a detergent, wash the jar in the sink. Rinse thoroughly. Place the jar in a cooking pot, and pour boiling water over it. Wait a minute or two and remove carefully with a jar lifter.

      Alternatively, you can pour cold water over and around the jar and bring the water to a boil, cook for a few minutes. Then remove carefully from the pot.

      Check out a post on Wikihow for more tips on sterilizing jars.
    3. You don’t have to measure the amounts exactly. A general rule of thumb is: “one part of flour to three parts of water”. For the size of our jar, drop in ⅔ US cup (100 g) of rye flour.
    4. Pour a little bit (3-4 tablespoons) of boiling water in and mix well with a spoon. This will “wake up” the gluten present inside the flour.
    5. If you got some gooey mud at this stage - you’re in the right spot.
    6. Now, add the garlic. It’s also a good moment to add the spices in (all-spice berries, peppercorns, bay leaf, marjoram), but personally I skip this step - see my explanation under the “Notes” section.
    7. Fill the rest of the jar with cooled boiled water (or with water filtered using activated carbon filter). Mix everything together with a spoon. 
    8. We don’t want any bugs in our 'Zakwas'.  Cover the jar with a piece of muslin, cheesecloth, or any other natural cloth and secure it with an elastic band or a piece of string. For that purpose, I use a muslin square that I chop into smaller pieces.
    9. The flour needs to ferment for 4-5 days, ideally in a shaded, but warm spot - 77°F/25°C would be ideal.
    10. Check on the jar every day. There is no need to open it and stir it - just let it be. 
    11. In the first 3 days, you’ll notice tons of activity. If the garlic (or spices if you used any)  floats to the surface, I just rock the jar a little bit to submerge it.
    12. After 4-5 days at room temperature, 'Zakwas' is ready. The fragrance should be pleasant: distinctively sour, but not overbearing, not razor-sharp.
    13. Once it’s done fermenting, screw the lid on and keep 'Zakwas' in the fridge. It will be good for 2 weeks.
    14. Now you can use your Rye Starter to make Żurek Soup. If you skipped the spices in 'Zakwas' (as I usually do), remember to add them when brewing the soup.

Notes

Many recipes for Rye Flour Starter include spices, such as all-spice berries, bay leaves and more. 

Personally, I avoid them. They don’t seem to improve the fermentation process. In fact, they tend to float to the surface, inducing mould formation - and the whole jar of spoiled ‘Zakwas’ has to end up in a bin. Since the starter ends up in a soup anyway, I choose to spice the soup instead.

You can try both methods and see what works better for you.

Save this “Rye Starter for Sour Rye Soup” recipe to your “POLISH FERMENTATION” Pinterest board! And let’s be friends on Pinterest!

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Kasia Kronenberger Polish food blogger

Cześć, I’m Kasia.

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