Name: Żur z Kaszub: a Kashubian rye soup with fermented rye base
Prep time: 25 min
Cook time: 30 min
Total time: 4375 min
Yield: 6 servings
Cuisine: Polish
Ingredients: 100 g wholemeal rye flour; 1 L water, boiled and cooled to lukewarm; 10 g garlic, crushed; 25 g established active rye sourdough starter; 1.2 L water; 600 g waxy or all-purpose potatoes, peeled; 8 g fine salt; 2 g dried marjoram; 1 g ground black pepper

Kashubian rye soup with potato pieces beside a glass jar of cloudy fermented rye base.

Yield 6 servings

Serving size about 400 ml

Active preparation 25 minutes, plus roughly 3 days for the ferment

Cooking time about 30 minutes

Ingredients ↓

Recipe at a glance

Żur z Kaszub: a Kashubian rye soup with fermented rye base

Żur z Kaszub begins with a cloudy, garlic-scented rye ferment. Here, that tangy base becomes a simple meatless potato soup, a measured home version of the Kashubian Lenten food tradition. Give the ferment about three days, then let its bubbles, aroma and acidity—not the calendar alone—tell you when it is ready.

In Kashubia, żur was a sustaining fasting food, especially during Lent. The Polish Ministry of Agriculture’s Traditional Products List describes Żur z Kaszub as a pale, cloudy liquid with rye-flour sediment and a sour garlic aroma. That description is of the fermented rye base, which is then used to cook soup or add acidity to other foods; the registry does not publish a measured soup recipe.

Local Kashubian food accounts describe whole rye flour, garlic and water left to sour for at least three days, then combined with potatoes, marjoram and pepper. A regional government publication notes that traditional Lenten żur was usually served without bacon garnish. This recipe follows that meatless direction and sets practical quantities for a six-serving home batch. The established rye starter and pH check are modern consistency and safety controls, not claims about the historic method.

The ferment should be cloudy, lightly bubbly and pleasantly sour, with the flour settling when left undisturbed. Stir or shake it before using so the sediment thickens the soup rather than staying at the bottom of the jar. Once the potatoes are tender, stir in the fermented base and simmer it thoroughly; raw flour must never be tasted or served.

This is a gentle, filling soup with a clean sour edge, soft potato cubes and garlic in the background. Keep it meatless for the documented fasting style, or serve it with bread if you want a fuller meal. The recipe itself does not include bacon or other garnish.

Tips for a good result

Use an established, active rye sourdough starter from a maintained culture. It helps the flour-and-water mixture acidify more consistently than relying on an unknown spontaneous ferment.
Use a clean glass vessel and a loose lid. Fermentation releases gas, so do not seal the jar tightly.
Keep the mixture at 20–24°C and check it at around 72 hours. It should be bubbly, smell pleasantly sour and measure pH 4.6 or below. Continue fermenting and checking if it has not reached that point; never use it while the pH is higher.
Flour is raw. Do not taste the ferment, batter, or flour sediment before it has been cooked. Discard the whole batch if you see colored or fuzzy mold, smell a putrid odor, or cannot get the pH to 4.6 or below.
The flour settles as the ferment stands. Stir it well before adding it to the soup for a smooth, evenly thickened broth.
Add the fermented base only after the potatoes are tender. Simmer gently for at least five minutes, stirring the bottom of the pan, so the flour cooks through without scorching.

Ingredients

Fermented rye base

100 g wholemeal rye flour
1 L water, boiled and cooled to lukewarm
10 g garlic, crushed
25 g established active rye sourdough starter

Soup

1.2 L water
600 g waxy or all-purpose potatoes, peeled
8 g fine salt
2 g dried marjoram
1 g ground black pepper

Method

Directions

Start the rye fermentWash your hands and use a clean glass jar and spoon. Whisk the rye flour into the boiled, cooled water until no dry pockets remain. Stir in the crushed garlic and active rye starter. Cover loosely so gas can escape while dust stays out. Ferment at 20–24°C for about 72 hours. Do not taste it raw. When ready, it should show active bubbles, smell pleasantly sour and measure pH 4.6 or below. If it has not reached that acidity, continue fermenting and check again; discard it if colored or fuzzy mold appears or the smell turns putrid.
Cut and simmer the potatoesPeel the potatoes and cut them into even 2 cm cubes so they soften at about the same pace. Add the soup water and salt to a heavy saucepan. Bring to a boil, add the potatoes, then lower the heat and simmer for 15–20 minutes, until a fork slips easily into a cube.
Stir the ferment into the potStir the rye ferment thoroughly to lift the flour sediment from the bottom. Pour the full batch into the potatoes and cooking liquid in a steady stream, stirring continuously. Add the marjoram and black pepper. The broth will become cloudy and lightly thickened.
Cook the sour soup throughBring the soup back to a gentle simmer and cook for at least five minutes, stirring along the pan bottom so the rye flour does not catch. Taste only after this cooking step, then adjust salt if needed. The potatoes should remain tender and intact; the broth should taste pleasantly sour and garlicky.
Serve and chill any leftoversLadle the hot soup into warm bowls. Stir the pot between servings because some flour may settle. If you will not serve the soup within two hours, divide it into shallow containers and refrigerate at or below 4°C. Use within 3–4 days; reheat soup to a rolling boil.

Estimated nutrition per serving

Energy140 kcal
Carbohydrate35 g
Protein4 g
Fat1 g
Fibre5 g
Sodium550 mg
Allergensrye, a gluten-containing cereal

Approximate values for one of six servings, without bread or optional toppings: Values are estimates based on wholemeal rye flour, potatoes and measured salt. The amount of flour sediment that remains in the soup and the size of each bowl can change the final values.

Serving, make-ahead and storage: Serve Żur z Kaszub hot as a light meal or first course. The measured version is meatless, reflecting the fasting style described in regional accounts. Rye bread makes a simple accompaniment, but it is not included in the ingredient quantities. Since rye contains gluten, this soup is not gluten-free.

Serving, make-ahead and storage: The ferment takes about three days and can be prepared ahead. Check its acidity before using; if it is not bubbly, pleasantly sour and at pH 4.6 or below, let it continue fermenting and recheck it. Do not taste the raw mixture. Once the soup is cooked, cool it quickly in shallow containers and refrigerate within two hours at or below 4°C.

Serving, make-ahead and storage: Keep leftovers chilled and use them within 3–4 days. Reheat only the portion you need, bringing soup to a rolling boil while stirring. Add a splash of boiling water if the soup has thickened in the refrigerator. Do not leave the pot at room temperature to cool slowly.

Frequently asked questions

Is Żur z Kaszub the soup or the fermented base?

The Ministry registry’s sensory description is of the fermented rye base: a cloudy, sour, garlic-scented liquid with flour sediment. Regional cooking accounts show that this base is then used to make potato soup. This recipe includes both stages so you can prepare the soup at home.

Why does the ferment need an active rye starter and a pH check?

The active starter helps a home batch sour more consistently. Flour is raw, so do not taste the uncooked mixture. Use the ferment only when it is actively bubbling, smells pleasantly sour and measures pH 4.6 or below, then simmer it in the soup for at least five minutes.

Can I add bacon?

Some regional descriptions include an onion-and-pork-fat garnish, while another regional account says the Lenten soup was usually served without bacon. This version keeps the measured recipe meatless; adding bacon would change its fasting character and nutrition.