Kvass: Nutrients, What Research Shows and Safety
Kvass is a lightly sour, fizzy drink fermented from rye bread. What one lab study measured for alcohol, sugar and fiber, and safety points on gluten, sugar and alcohol.
Content last updated . This page has not been medically reviewed.
Kvass is a traditional Eastern European drink made by fermenting rye bread (or dried bread rusks) in sweetened water. Yeast and lactic acid bacteria work together, so the drink becomes slightly sour, gently fizzy and deep brown. [1] People drink it cold in summer, and some say it is a "probiotic" or a "healthy soda." This page keeps real fermented kvass apart from bottled drinks sold under the same name, and says what is and is not shown.
Read this first
- Bottled "kvass" is not always fermented kvass. A Polish study notes that many drinks sold as kvass are made from malt concentrate with additives, not from bread fermented by yeast and bacteria. [1]
- Trace alcohol: in that study, lab-made bread kvass had about 0.34% alcohol by volume, and the authors say it stays under 0.5%. Two commercial drinks tested had none. [1] Home batches left to ferment longer may differ; we did not read measurements of home batches.
- Sugar varies a lot: the same study found about 4 to 4.6 g sugar per 100 mL in the bread-fermented kvass and one bread-based commercial drink, but 12 g per 100 mL in another commercial "kvass." [1]
- Gluten: kvass made from rye bread is made from a gluten grain. NIDDK lists wheat, barley and rye as the grains that trigger celiac disease. [3] Do not assume it is gluten-free.
- Evidence in one line: we did not find a trial of kvass in people. The health claims rest on lab composition and general reviews. [1] [2]
What is in it (USDA values)
The USDA data file for kvass is empty, so we show no USDA numbers or % Daily Value. The values below come from one peer-reviewed food-science study (Gambuś et al., 2015, University of Agriculture in Krakow) that made kvass from wholemeal rye bread in the lab and compared it with two commercial drinks. [1] These are per 100 mL of drink in that study.
| Measure | Lab-made kvass from wholemeal rye bread | Commercial bread-based kvass | Commercial malt-concentrate drink |
|---|---|---|---|
| Alcohol (% by volume) | 0.34 | 0.00 | 0.00 |
| Sugars (g per 100 mL) | 4.1 to 4.6 | 4.2 | 12.0 |
| Dietary fiber (g per 100 mL) | 0.3 to 0.5 | 0.2 | 0.1 |
| Protein (% of dry matter) | 0.12 to 0.13 | 0.1 | 0.3 |
For a standard 240 mL glass, simple arithmetic from those numbers gives roughly 10 to 11 g sugar for the lab-made kvass and about 29 g for the sweetest commercial drink. These are rough figures for one study and will not match every product. The paper's introduction also quotes about 32 kcal per 100 g and says kvass is rich in B vitamins, but it cites other authors for this and the study did not measure vitamins itself. [1] The study found zinc and copper far too low to matter nutritionally. [1]
Plant compounds: the authors report higher antioxidant activity in their lab-made kvass than in commercial ones, but the increase came mostly from added caramel and citric acid, not from the fermentation. [1] This is a lab measurement, not a health effect in people.
What research says
| Health goal | What the sources found | Strength of evidence | What was studied |
|---|---|---|---|
| Fiber and sugar compared with soda | Lab-made kvass had about twice the fiber of the commercial drinks and about one third of the sugar of the sweetest one. [1] The amounts of fiber are small (0.3 to 0.5 g per 100 mL). | Lab or animal only (composition, not a health outcome) | One lab study, 3 drinks |
| Antioxidant activity | Higher in lab-made kvass, mainly due to caramel and citric acid additions. [1] | Lab or animal only | Lab test tube assays |
| Gut bacteria / probiotic effect | The authors say true kvass can be considered probiotic if made by natural fermentation without heat treatment, but they did not test it in people. [1] A 2025 review of Eastern European fermented foods says artisanal variability and few standardized human studies limit firm conclusions. [2] A review of human trials of traditional fermented foods found that many are understudied. [8] A general review says microbes from fermented foods may pass through the gut and that effects depend on the food and the person. [7] | Insufficient evidence | Reviews and lab work |
| Blood pressure peptides | The same 2025 review reports peptides with blood-pressure-lowering effects in fermented foods generally. [2] | Lab or animal only for kvass | Narrative review |
| Digestive complaints, metabolism | Claims in the paper's introduction are cited to secondary authors and not tested. [1] | No good evidence of benefit found in the sources we read | Not tested |
Eaten as food vs taken as a supplement. Everything above is the drink. We did not read a trial of a kvass extract or supplement. For the difference between live fermented foods and probiotic supplements, see fermented foods vs probiotic supplements.
How much is a normal serving
We did not find an official serving size for kvass (USDA, MyPlate, NHS or EFSA). For comparison, 240 mL (about 1 cup) is a common glass size, which is how we did the sugar arithmetic above. That is information, not a prescription.
Safety, allergy and medicines
- Gluten and celiac disease: rye contains gluten. [3] Bread kvass is not safe for people with celiac disease, and malt-concentrate drinks use rye and barley malt. [1] Check labels.
- Alcohol: alcohol is a by-product of the yeast. The lab-made kvass had 0.34% by volume. [1] If you avoid alcohol completely (for example in pregnancy, in recovery, or with certain medicines), choose a product labeled alcohol-free and ask your doctor. We did not read an official statement about trace-alcohol fermented drinks.
- Sugar and diabetes: sugar differed more than threefold between the drinks tested. [1] People with diabetes should read the label.
- Children: the authors say natural kvass can be given to all ages because the alcohol is a trace. [1] That is the authors' view in one paper, not official guidance. We did not read a pediatric source.
- Allergy: rye is a gluten grain but not one of the nine major US allergens (milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, soy and sesame). [4] Some kvass has flavors such as raisins, honey or other ingredients. Call 911 for trouble breathing or swelling of the face, lips or throat.
- Medicines: we did not read any source describing a direct interaction between kvass and a medicine. Yeast extracts and fermented soy foods can matter for MAOI antidepressants, but kvass is not named in the source we read. [5] Ask a pharmacist if you take one.
- Kidney disease: we did not read potassium or phosphorus values for kvass.
- Home fermentation: official home-fermentation advice says to use tested recipes and not to cut the salt or change the acidity in vegetable ferments. [6] We found no official guidance for kvass. Use clean bottles, do not seal them tightly during active fermentation (pressure can build), and discard a batch that looks moldy or smells rotten.
Choosing, storing and food safety
- Look for the ingredient list: bread, water, sugar and yeast mean a fermented drink; "malt concentrate" or added flavors mean a different product. [1]
- A live, unpasteurized kvass keeps fermenting, so it should be kept cold. The authors say a proven recipe can be made at home and kept in the refrigerator for several weeks. [1]
- The authors say kvass can only be called probiotic if it is made by natural fermentation and not heat-treated. [1] Check the label for "pasteurized" or "live."
Related pages
Health connections for Kvass
What research links to eating or drinking this food, and how strong the evidence is. Many studies are observational or use juice, powder, oil or extracts rather than the food as eaten; each card says which.
Kvass compared with soda: sugar and fiber
Lab or animal research onlyIn one lab study, bread kvass had about 4.1 to 4.6 g sugar and 0.3 to 0.5 g fiber per 100 mL, versus 12 g sugar and 0.1 g fiber in a malt-concentrate drink sold as kvass. Amounts of fiber are small.
Supplements: Dietary role only; this is a food, not a supplement. No supplement was tested.
Antioxidant activity of kvass
Lab or animal research onlyLab-made kvass had higher antioxidant activity than commercial drinks, but the increase came mostly from added caramel and citric acid, not from fermentation.
Supplements: Dietary role only; this is a food, not a supplement. No supplement was tested.
Kvass as a probiotic or gut-health drink
Not enough evidenceThe authors say naturally fermented, non-heat-treated kvass could count as probiotic but did not test it in people. A 2025 review says few standardized human studies exist for Eastern European ferments.
Supplements: Dietary role only; this is a food, not a supplement. No supplement was tested.
Fermented foods and blood-pressure peptides
Lab or animal research onlyA 2025 review reports peptides with blood-pressure-lowering effects in Eastern European fermented foods in general; not shown for kvass in people.
Supplements: Dietary role only; this is a food, not a supplement. No supplement was tested.
Connected topics
Open a group to see how each topic connects and how strong the evidence is.
Health goals (1)
- Blood Sugar BalanceDocumented risk
Sugar differed more than threefold between the drinks tested (about 4 to 12 g per 100 mL); read the label if you watch sugar.
Root causes (1)
- Poor DietDocumented risk
Some bottled drinks sold as kvass have much more sugar (12 g per 100 mL) than bread-fermented kvass.
Conditions & symptoms (1)
- Celiac DiseaseDocumented risk
Kvass made from rye bread contains gluten; people with celiac disease should avoid it unless the product is certified gluten-free.
Documented risks and interactions (4)
- Trace alcohol in kvass. Lab-made bread kvass had about 0.34% alcohol by volume, and the authors say natural kvass stays under 0.5%. Two commercial drinks had none. Longer or warmer home batches were not measured in the sources we read.
- Gluten in rye-bread kvass. Rye is a gluten grain (NIDDK lists wheat, barley, rye). Bread kvass is not gluten-free by default.
- Home fermentation safety. Official home-fermentation advice is written for vegetables and stresses tested recipes and clean equipment. We found no kvass-specific guidance.
- Food allergy and emergency signs. Rye is not one of the nine major US allergens, but flavorings or other ingredients may be. Trouble breathing or swelling needs emergency care.
Frequently asked questions
Is kvass alcoholic?
In one lab study, bread kvass had about 0.34% alcohol by volume, and the authors say natural kvass stays under 0.5%. [1] Two commercial drinks had none. If you must avoid all alcohol, choose an alcohol-free product.
Is kvass gluten-free?
No, not when it is made from rye bread. Rye is a gluten grain. [3] Check labels if you have celiac disease.
Is kvass a probiotic?
The authors say naturally fermented kvass that is not heat-treated could be considered probiotic, but they did not test it in people. [1] A review says human studies on traditional Eastern European ferments are few. [2]
Is kvass healthier than soda?
In one study, lab-made kvass had about a third of the sugar of the sweetest commercial drink and some fiber. [1] That does not prove health benefits. Compare labels, because some bottled drinks have a lot of sugar.
Can I make kvass at home safely?
Official home-fermentation advice is written for vegetables and stresses tested recipes and clean equipment. [6] We found no kvass-specific official guidance, so ask a local food-safety extension service.
References
- Gambuś H et al. Health benefits of kvass manufactured from rye wholemeal bread. J Microbiol Biotech Food Sci 2015;4(special issue 3):34-39 (full text read; funding not stated in the text we read). Read 2026-10-24.
- Zugravu CA, Constantin C. Eastern European fermented foods: nutritional value, functional potential, and cultural heritage. Foods 2025 (abstract read via Europe PMC). Read 2026-10-24.
- NIDDK. Celiac disease: definition and facts. Last reviewed October 2020. Read 2026-10-24.
- FDA. Food allergies. Page current as of 2026-03-11. Read 2026-10-24.
- Easton-Carr R, Schaffer DH. Monoamine oxidase inhibitor toxicity. StatPearls (page shows update August 2026). Read 2026-10-24.
- National Center for Home Food Preservation. General information on fermenting. Undated page. Read 2026-10-24.
- Park I, Mannaa M. Fermented foods as functional systems: microbial communities and metabolites influencing gut health and systemic outcomes. 2025 (abstract read via Europe PMC). Read 2026-10-24.
- Santa D et al. Health benefits of ethnic fermented foods. Front Nutr 2025 (abstract read via Europe PMC). Read 2026-10-24.