Beet kvass is a salty, sour, deep-red drink made by fermenting chunks of raw beetroot in salted water for a few days. It’s the beet cousin of bread kvass in name only – there’s no bread or yeast – and in Eastern European kitchens fermented beet liquid is also used to sour soups such as borscht. It tastes earthy and tangy, like the brine of fermented beets, because that’s essentially what it is: more water, fewer beets, strained after a short ferment.
How It Works
Lactic acid bacteria that live on the beets turn some of their sugar into lactic acid, souring the liquid and keeping out spoilage microbes – the same process as any brined vegetable. The rules are the same too: weigh the salt, keep the beets under the liquid (the bacteria don’t need air; molds do), and keep the jar at cool room temperature (NCHFP).
Spontaneous fermentation is a little unpredictable. In a Polish study of fermented red beetroot, adding a starter of lactic acid bacteria let Lactobacillus dominate and cut the share of spoilage bacteria compared with jars left to ferment on their own, and a multi-strain starter largely prevented histamine from forming (Choińska et al., 2022). At home, a few spoonfuls of brine from an active, sour vegetable ferment does a similar job.
Salt: Why 2%
Many beet kvass recipes call for “a teaspoon of salt per quart”. That’s only about 0.6% – too little to hold back spoilage bacteria reliably while the acid builds, and the usual reason a batch turns slimy or smells rotten. Weigh it instead: 20 g of non-iodized salt per litre of water (2%). Any non-iodized salt works; anti-caking agents can cloud the brine but don’t stop fermentation.
What Beet Kvass Can and Can’t Do
Unpasteurized beet kvass contains live lactic acid bacteria, and fermentation changes the beets’ pigments and polyphenols – lab studies of fermented beet juice report new betalain forms and higher antioxidant readings in test tubes (Sawicki et al., 2024). That’s not the same as a health effect in people. The blood-pressure evidence for beets comes from trials of beetroot juice in people with high blood pressure (Benjamim et al., 2022), which delivers far more of the beets’ nitrate than a glass of diluted kvass. Drink it because you like it – and remember it’s salty: a 120 ml (½ cup) glass of 2% brine holds about 2.4 g of salt.
Red urine or stools after eating beets is a harmless effect of the pigment. If the kvass smells rotten rather than sour, turns slimy or grows fuzzy mold, discard it (NCHFP); our fermentation troubleshooting guide explains the harmless white film (kahm yeast) as well.
Ways to Use It
- Chilled in a small glass, or topped up with sparkling water.
- To sour and color borscht and other beet soups – add it at the end so it doesn’t boil.
- In vinaigrettes: 3 parts oil, 1 part beet kvass, a little mustard.
- Flavor variations: a few slices of ginger, a strip of orange peel, or garlic and dill in the jar.
