Beetroot Kvass is a tangy, deep-red fermented drink, and in my kitchen it mostly earns its keep as the base for a proper Polish beetroot soup. A good barszcz starts with a good kvass, so this is where that flavour really begins.
It could not be much simpler: raw beetroot, water and salt, with garlic, bay, allspice and peppercorns going in alongside them, then about a week on the counter while the fermentation does the work. It comes out sour and savoury rather than sweet, and full of the live bacteria plenty of people ferment for. I use beetroot from my own allotment, which is sweeter and nowhere near as bitter as a lot of what the shops sell, so if you are buying, look for organic.
I use mine in my Polish Beetroot Soup (Barszcz), but plenty of people drink it on its own as a probiotic. Take it a small glass at a time rather than by the tumbler, because it is salty, and dilute it with water if it is too much. Fermenting is one of the foundations of Polish cooking, and my guide to Polish food covers that pantry.
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Pin itKvass in the Polish Kitchen
Kvass is an old Slavic ferment, and the beetroot version earned its place in Polish and Ukrainian kitchens as the deep, earthy base for a proper barszcz, especially at Christmas Eve dinner. Plenty of people also drink it on its own for the gut. For another traditional Slavic ferment, try my Ogórki Kiszone, or for a jar with beetroot in it that you eat rather than drink, my fermented radish, carrot and beetroot.
The barszcz this kvass is made for is already on the site. Ukrainian borsch is a different soup, thick with cabbage and potato and eaten with a spoon, and that one I have never written. Iryna at Lavender & Macarons has a Ukrainian borsch I like very much.
What Water to Use for Fermentation?
Water quality is key to successful fermentation, as microbes thrive in clean water with plenty of natural minerals. I highly recommend using filtered or bottled water for the best results. A carbon water filter is an excellent option for removing chlorine, heavy metals, chemicals, and microplastics from tap water. Not only does this benefit your health, but it also creates an optimal environment for the microbes essential to fermentation.
If filtered or bottled water isn’t an option, you can still ferment with tap water. To make it more suitable, boil the water to remove chlorine and other impurities, then allow it to cool to room temperature before use. This extra step ensures a cleaner, more microbe-friendly environment, helping your fermentation process succeed.
What Salt is Best for Fermenting Foods?
While you can ferment foods with regular table salt, for the best quality and flavour, I recommend using unrefined sea salt or rock salt. These salts are rich in natural minerals that benefit both your health and the microbes essential for successful fermentation.
Want to scale this up or down? My fermentation brine calculator works out the exact salt for any batch size.
Every fermenting cook I have read says to avoid iodised table salt, and I would too, though the usual explanation - that the iodine kills the bacteria - is not something I can point to a study for. What is documented is smaller and more practical: iodide reacts with the chlorine in tap water and can throw a faint seaweed-like smell, and table salt also carries anti-caking additives that do not dissolve cleanly and cloud a brine, which is exactly why salts sold for pickling leave them out. Unrefined sea salt or rock salt, then, and you avoid the whole question.
How Salty, and How Warm
My brine is a strong one and it is worth knowing that before you taste it: 20 g of salt to 400 ml of water, which is about five per cent of the water. Most kvass written for drinking sits nearer two, so mine is noticeably saltier than the average.
That is deliberate, because of where most of mine ends up. A kvass made for barszcz gets stirred into a whole pot of soup at the end, so the salt disappears into it and the sourness is what you are actually after. If yours is going into a glass rather than a pan, either dilute it with water when you pour it, or make the next batch with 8 to 10 g of salt instead and expect it to ferment a little faster.
Temperature matters more than most recipes admit. An ordinary warm room, somewhere around 18 to 21°C, is the range this wants. Do not start it in the fridge, which is simply too cold to get going. A British kitchen in winter sits right at the bottom of that range, so expect a slow ferment rather than a failed one - give it longer and keep tasting instead of adding more salt or more warmth. A very warm kitchen is the other risk, and it is the one readers blame most often when a batch goes mouldy.
Equipment You’ll Need
Barely any kit, but the jar itself does real work.
A Closer Look at the Ingredients
Only a few things go into beet kvass:
- Raw beetroot the base; it ferments into a deep, earthy tonic.
- Water filtered if your tap water is heavily chlorinated (see the water note above).
- Rock (non-iodised) salt to guide a clean ferment.
- Optional garlic, bay or caraway for extra flavour.
Chef’s tip: trust your nose. Good kvass smells earthy and sour in a pleasant way at every stage, and it is meant to go hazy and lively as it works - that cloudiness is the bacteria doing their job, not a fault. What you are watching for is different: liquid that has turned thick, ropey or slimy when you pour it, fuzzy patches of green, black or pink, or a smell that is genuinely bad rather than merely sour. Any of those and the batch goes.
How to Make Beetroot Kvass, Step by Step
Five steps, the same five as the recipe card, with the reasons written in.
- Make the brine. Stir 20 g of salt into 400 ml of lukewarm water until it has completely dissolved, and let it come back to room temperature before it meets the beetroot. Lukewarm simply helps the salt go into solution; hot water would set the ferment off badly. If your tap water is heavily chlorinated, boil it and let it cool first, or use filtered, because chlorine is there to kill exactly the sort of bacteria you are trying to encourage.
- Fill the jar. Slice the beetroot into pieces about the thickness of a pound coin - slices rather than grated or blitzed, which matters more than it sounds. Cutting it finer releases far more sugar at once, and a sugar rush is what pushes a ferment towards alcohol instead of a clean sourness. Pack it into a clean 1 litre glass jar with the garlic, bay leaves, allspice berries and peppercorns. Glass or glazed ceramic only: salt and acid will react with metal and scratched plastic holds onto whatever fermented in it last.
- Cover everything with the brine. Pour it over until every piece is under the liquid, and leave a couple of centimetres of space at the top. This is the step that decides whether you get mould: anything sitting proud of the brine is in contact with air, and that is where fuzzy patches start. A small glass weight, a clean jam jar lid or even a folded cabbage leaf will hold the pieces down if they keep bobbing up.
- Leave it to ferment. Close the jar loosely or fit an airlock - not tight, because fermentation makes gas and a sealed jar builds pressure until something gives. Stand it out of direct sunlight somewhere around room temperature and leave it for seven to ten days. From day three, taste a spoonful every couple of days: it should be getting sourer and more savoury, and the colour should be deepening to something close to ink. It will go cloudy and may fizz gently, and both are signs it is working. Stop when it tastes right to you rather than when the calendar says so.
- Strain it and chill it. Pour it through a sieve, keeping the liquid and pressing nothing through. Bottle it in a clean jar and put it in the fridge, where the cold slows the fermentation almost to a stop and it will keep two to three weeks. It carries on souring very slowly in there, so an older bottle is sharper than a fresh one, which is no bad thing in a soup. Do not throw the beetroot away either: it is good chopped into a salad or eaten as it is.
Recipe Card for Beetroot Kvass
Beetroot Kvass Recipe: Traditional Base for Borscht & Medicinal Tonic
Learn how to make traditional Beetroot Kvass, a fermented drink perfect as a borscht base or a healthy probiotic tonic for gut health
Equipment I Use
Ingredients
Instructions
Close the jar loosely or with an airlock and store it away from direct sunlight at room temperature.
Allow the fermentation to proceed for 7 to 10 days. Check the aroma and taste every few days.
Once the kvass has developed a tangy, earthy flavour, remove the beets and other solids from the liquid. You can use a sieve for separation.
Transfer the kvass to the fridge to slow down the fermentation. It will keep for a few weeks.
Chef’s notes
This is a strong brine, about five per cent of the water, which suits a kvass destined for barszcz. If you are drinking it rather than cooking with it, dilute it in the glass or use 8 to 10 g of salt next time.
Slice the beetroot, do not grate it. Cutting it finer releases sugar too fast and pushes the ferment towards alcohol instead of a clean sourness.
Everything under the brine. Anything sitting proud of the liquid is where mould starts. Weigh the pieces down if they float.
Room temperature, about 18 to 21C, and never the fridge to start. A cold kitchen means a slow ferment rather than a failed one, so give it longer and keep tasting.
Cloudy is normal. Discard it only for thick or ropey liquid, fuzzy coloured mould, or a smell that is off rather than sour. A flat white film is usually kahm yeast: skim it and carry on.
Nutrition per serving
Check out my other Recipes:
Fermentation Tips and Troubleshooting
Fermentation is an art, and even the smallest details can make a big difference. Here are some tips to ensure your beet kvass turns out perfect every time:
- Keep it Clean: Always sterilise your jar and utensils with boiling water to prevent contamination.
- Submerge Ingredients Fully: Make sure the beets and spices are completely covered with brine to avoid mould growth.
- Choose the Right Environment: Store your jar at room temperature, away from direct sunlight, to maintain consistent fermentation conditions.
- Check the Aroma: During fermentation, your kvass should smell earthy and tangy. If it smells rotten or develops mould, discard it and start again.
Troubleshooting
- If the fermentation seems slow, ensure your water doesn’t contain chlorine, which can inhibit microbial growth.
- If your kvass tastes too salty, dilute it with water before drinking.
Storing and Shelf Life of Beet Kvass
Proper storage is key to maintaining the freshness and flavour of your Beet Kvass. Once the fermentation process is complete, strain the liquid and transfer it to a clean, airtight container. Store the kvass in the refrigerator, where the cool temperature will slow down further fermentation.
Beet Kvass will keep for 2-3 weeks in the fridge. For the best flavour and benefits, consume it within this time frame. If the taste becomes overly sour or the smell changes, it’s time to discard it. Always use clean utensils when pouring to avoid introducing contaminants that could spoil the kvass.
With proper care, your kvass will remain a refreshing and healthful addition to your diet!
Pin itFAQ for Beetroot Kvass
How do I know when my beetroot kvass is ready?
Taste and smell are your guides. It should smell pleasant and earthy and taste pleasantly tangy and savoury - and it should be clear, not cloudy. When it tastes good to you (usually several days to a couple of weeks), it is ready.
My kvass has gone cloudy. Is it ruined?
No, and a clear jar would be the odd one out. A lacto-ferment clouds as it works because the bacteria multiplying in it are what make it hazy, and ours goes deep and murky before it settles. The things that do mean throwing it away are liquid that has turned thick, ropey or slimy as you pour it, fuzzy coloured patches of mould, or a smell that is off rather than sour. A flat white film on the surface is neither of those - see the kahm yeast question below.
How long does it take to ferment?
Usually a few days to two weeks at room temperature, depending on how warm the room is - warmer ferments faster. Taste it regularly and stop when you like the flavour.
What do I use beetroot kvass for?
It is the traditional base for a deep, tangy barszcz (borscht), especially for Christmas Eve, and many people drink a small glass of it on its own as a health tonic.
How do I store it?
Once it tastes right, strain it and keep it in the fridge, where fermentation slows right down. It keeps for several weeks.
There is a white film on top - is my kvass mouldy?
Usually not. A thin white film is often kahm yeast, which is harmless - skim it off and carry on. True mould is fuzzy and coloured (green, black or pink); if you see that, throw the batch out and start again. Keeping the beetroot fully under the brine and giving the jar a gentle shake every couple of days helps prevent both.
How do I turn the kvass into barszcz?
Cook your barszcz first with the stock and vegetables, then stir the zakwas in at the very end and warm it through gently. Do not let it boil, or you lose the bright ruby colour and the good tang.
More recipes you’ll like
- Polish Żurek - Sour Rye Soup, the other Polish ferment that starts with a jar on the counter, and Mastering Kimchi in Vacuum Bags if you want to ferment without a crock
- Or my Bigos Królewski - Polish Hunter’s Stew and Authentic Polish Braised Cabbage
A Few Words from the Chef
Most of my kvass goes into barszcz rather than into a glass. Barszcz was my childhood favourite and it is the first thing on the table on Christmas Eve, and one built on kvass tastes nothing like one built on stock and vinegar. Tell me how yours turns out in the comments.
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