UPDATE: The most recent batches of the Original Quas were canned on Wed 17th of July. Order now.

Learn More About Kvass

Below you will find answers to the most frequently asked questions about kvass.

What is kvass?

Kvass is a 1000-year-old all-natural healthy fermented beverage made from rye and barley.

Learn what makes kvass different

How is Quas different from kvass available in shops?

In short, they are almost completely different drinks! Commercial kvass available in shops is made by diluting concentrate, mixing it with sugars and acidity regulators, and artificially carbonating it with carbon dioxide. Often, there is no fermentation involved at all! Other producers might use baker’s yeast for fermentation (without probiotic bacteria), which is then filtered out or killed by pasteurisation. Since yeast does not produce organic acids, acidity regulators and preservatives are added. In either case, commercial kvass does not have any health benefits, while the high sugar content is similar to that of a standard can of cola. You can easily recognise commercial kvass by looking at the best-before date, which can extend to 12-36 months at room temperature.

On the other hand, Quas is fermented using a sourdough starter culture where a rich community of over 100 types of good bacteria and yeast are present. After the fermentation process, Quas is not filtered or pasteurised, meaning that you get over 500 billion live bacteria with every can of Quas! We do not add preservatives, acidity regulators or artificial or natural flavours. All organic acids, vitamins and enzymes are naturally produced by the bacteria present in Quas. Moreover, Quas contains less than half of the sugar found in commercial kvass! We make fresh Quas weekly in small batches. After delivery, Quas always needs to be stored in the fridge and should be consumed within 4-8 weeks.

Why is kvass better than other healthy drinks?

‘Better’ is a very subjective definition, but genuine kvass takes the concept of ‘healthy’ to a completely new level! Let us explain. You probably know that vitamins and antioxidants are good for you. You often see them on product labels of natural products, such as orange juice, or artificially formulated products, such as vitamin-infused water. Natural sources of vitamins are almost always better for our body compared to artificially formulated supplements. However, the amount of sugar present in natural juices is often simply too much for our modern diets (orange juice: 8 g; apple juice: 10 g; pineapple juice: 14 g; Coca-Cola: 11 g per 100 mL). Meanwhile, nutrients and additives in artificially formulated zero-sugar products and food supplements are well-defined but limited. This is also why doctors often say that supplements do not constitute a healthy varied diet.

In contrast, kvass naturally contains vitamins (B1, B3, B2 and B6), dietary fibres and microelements (zinc and copper), while containing only 3.8 g of sugar per 100 mL (Ignat et al., 2020). Most importantly, the microorganisms present in kvass are able to produce thousands (!) of other molecules and enzymes with functional properties that are not present in other healthy drinks! These molecules, together with the live bacteria, are responsible for functions that are unique to the benefits attributed to probiotic products (Chung and Kamal-Eldin, 2020):

  • fighting harmful bacteria in the gut
  • enhancement of metabolic activities and nutritional value
  • antioxidant, anti-inflammatory and immune-modulating effects
  • reduction of allergies and improvement of gut function
  • reduction of cardiovascular disease risk
  • reduction of cancer risk

How is kvass different from kefir?

Both kvass and kefir are considered to be probiotic products since they both contain live cultures that benefit human health. Interestingly, they also both originate from the same geographical region - Eastern Europe. There are, however, some important differences. Kvass is made from fermented cereal grains (rye and barley) using sourdough, while kefir is made from fermented milk using kefir grains. Because of that, kefir naturally contains lactose, which you might want to avoid if you have lactose intolerance. However, genuine kefir produced from kefir grains on small independent farms is one of the best probiotic products that you can buy on the market today!

The key differences stem from the starter culture that is used for fermentation (kefir grains vs sourdough). Genuine kefir milk produced using kefir grains contains 22-61 strains of different bacteria and is dominated by Lactococcus spp. which belongs to the Streptococcaceae family (Bourrie et al., 2016). Only a few species of Lactococcus have been confirmed to have useful health benefits (Kondrotiene et al., 2020). In contrast, we have found at least 132 different types of bacteria present in kvass. This rich diversity is dominated by Lactobacillus spp. which belongs to the Lactobacillaceae family. Interestingly, the majority of known probiotic strains belong to Lactobacillus spp. (Frakolaki et al., 2020). In kvass, there are at least 20 different types of bacteria that belong to this group!

How is kvass different from kombucha?

The cultures of kvass are dominated by lactic acid bacteria (LAB), while kombucha’s culture is dominated by acetic acid-producing bacteria (AAB), which results in a vinegary taste that is off-putting for some people. More importantly, the ingredients used for kombucha production (tea and sugar), simply do not contain the microbial diversity that would match the lost diversity in the modern population. This is because kombucha cultures are dominated by the Acetobacteraceae family, while the majority of the known probiotic bacteria belong to the Lactobacillaceae family (Gaggia et al., 2019; Frakolaki et al., 2020). In contrast, cereals (e.g. bread, grains, malts) that could be used for the fermentation of kvass provide a natural environment for the cultivation of the microbial community of bacteria that well matches the lost community of the gut (Ignat et al., 2020)!

If you enjoy kombucha, double-check the best-before date next time you pick a bottle. Does it expire in 3, 6 or 12 months from now? A recent 3 months study found that although yeasts in kombucha survived 3-months of storage, the number of live acetic acid bacteria was significantly reduced after 1.5 months (Grassi et al., 2022). Importantly, the most beneficial lactic acid bacteria in kombucha were reduced after just 3 days of storage in the fridge so that by day 20 no live bacteria were alive.

How is kvass different from other probiotic drinks?

Unlike the majority of mainstream probiotic beverages, kvass is lactose-free, caffeine-free and vegan. Probiotic drinks made by large brands such as Actimel, Yakult and Biomel only contain 1-3 types of probiotic bacteria and up to 20 billion colony-forming units (CFU) per dose. Since our gut microbiome normally contains 500-1000 types of different bacteria, these probiotic drinks are like a drop in the ocean when it comes to increasing the diversity of the gut microbiome. In contrast, Quas is made using our natural 180-year-old sourdough starter culture, which contains over 100 types of bacteria and yeast! Moreover, each can contains at least 500 billion CFU of live bacteria, making it the most concentrated and most strain-diverse probiotic product on the market in the UK today.

How is kvass different from probiotic supplements?

Probiotic supplements contain bacteria that have been grown in the lab and then either formulated into a liquid product or dried into a powder and packed into pills. The issue is that we still cannot grow the vast majority of the bacteria (Lewis et al., 2020)! As a result, this limits the variety of probiotic bacteria that we can get from supplements. Moreover, many bacteria simply do not survive the drying process or die later in storage before arriving in your gut. In contrast, we make Quas weekly in small batches with a shelf-life of 4-8 weeks in the fridge. This ensures that by the time you have a can of Quas, the majority of the probiotic bacteria are happy and alive! That is why we call it ‘Live Fermented Quas’!

What is the difference between kvass and beer/non-alcoholic beer?

Kvass and beer are both produced during the fermentation of cereal grains. However, they are completely different products! Most modern beer is brewed with hops using alcoholic fermentation which normally continues until yeast converts all available sugars in beer into alcohol and carbon dioxide. In some sour beers, lactic acid bacteria (LAB) are added to create sourness. After the fermentation, the yeast is removed using filtration and the final beer is often pasteurised to deactivate the remaining yeast.

Production of low- or non-alcoholic beer, is somewhat similar, with the exception that the alcohol is either removed from the final product or the fermentation step is modified to produce limited alcohol content (Salanta et al., 2020). However, in either case, the final packaged beer does not contain any live yeast or bacteria.

In contrast, genuine kvass is always produced using mixed cultures of bacteria and yeast, and is never filtered or pasteurised at the end. The fermentation of kvass is unfinished, meaning there are still fermentable sugars present in each can that microorganisms can feed off. This is also why you can taste a bit of sweetness in kvass compared to beer. Also, the traditional kvass recipe does not include hops, so all the rich fruity flavours are created by the bacteria and yeast during the fermentation!

If you are looking for a healthier option, a can of Quas (330 mL) contains 64-65 calories, which is slightly less than average non-alcoholic beer (70 cal) and much less than full-strength alcoholic beer (150 cal) (free-beer.co.uk). Most importantly, beer and alcohol consumption overall brings more harm than benefit to your health (Wikipedia). In contrast, every can of kvass will only make you feel better and healthier from so many different perspectives!


Is kvass a non-alcoholic beverage?

Similar to fermented drinks such as kombucha and kefir, kvass is considered a non-alcoholic beverage. However, a small amount of alcohol is naturally produced during the fermentation process in all of these products. At Quas we thoroughly monitor and control the alcohol content, so most likely your can of Quas will contain about 0.5-0.75% (ABV) of alcohol.

Interestingly, according to NHS, 1 unit of alcohol is the amount of alcohol the average adult can process in 1 hour. In our case, 0.75% (ABV) in a 330 mL can is about 0.25 units, which should be completely gone from your body within just 15 minutes!

Is kvass vegetarian/vegan?

Kvass is made from fermented rye and barley. Ginger kvass also contains 10 grams of freshly pressed ginger. In addition to cereals, spiced kvass contains spices. No products of animal origin are used during the production process. Therefore, kvass is both vegetarian and vegan friendly.

What is the shelf-life of Quas?

The shelf-life of kvass is around 4-8 weeks from the moment you receive your order. Always remember that Quas can only be stored in the fridge. This is a relatively short shelf-life compared to other soft drinks or non-alcoholic beers. However, it ensures that whenever you decide to have a can of Quas, the good bacteria and yeast inside are alive and happy!

Quas is still completely safe to drink even after the best-before date! We also found over a billion live bacteria present even 8 months after the best-before date. However, by that point, the majority of sugars will be converted into organic acids, which will make Quas appear more sour than you might like it.

Why does Quas need to be always refrigerated?

Genuine kvass contains live cultures of bacteria and yeast that are still active. By lowering the temperature, we slow down their activity while still making sure they are alive and happy.

You might wonder how come Quas is not refrigerated during delivery? Fermentation is a complex process and we spent a lot of time optimising every parameter to make sure you get your order in the best condition. Our production process is designed in a way that allows kvass to be not refrigerated during delivery. However, you must keep Quas in the fridge at all times after receiving your order.

What happens to Quas in your fridge?

Quas is a live product, so you can think of every can as a miniature bioreactor! At low temperatures in the fridge, the live biological processes in Quas are slowed down, but they are still active. This means that even in the fridge, these live bacteria and yeast continue slowly eating sugars and making organic acids, vitamins, enzymes, carbon dioxide and alcohol, among other things. As time goes on, Quas gets slightly more sour and less sweet. You should expect Quas to taste like kvass within the best-before date. It tastes a little too sour to our liking after that, however, it is still absolutely safe to drink!

Why is Quas not filtered or pasteurised?

The filtration or pasteurisation step is added to either physically remove live microorganisms from the product or simply kill them with heat. This helps to prevent food spoilage and extend shelf-life. Think of a long-life/UHT milk. However, the health benefits of kvass actually come from the live microorganisms present in each can! At Quas, our goal is to make products of the highest quality while giving the priority to human health, even if it comes at a cost of a shorter shelf-life

How do we know how many live bacteria there are in Quas?

Because we counted them! We regularly take samples of Quas for analysis to make sure our kvass is of the highest quality. Part of the process includes counting the number of live bacteria present in 1 mL of Quas. Because there are so many bacteria in Quas, we first need to dilute it to be able to count the bacteria. After diluting Quas 1 million times (!), we transfer tiny droplets of diluted Quas onto a petri dish containing special growth media. A few days later, separate ‘colonies’ of bacteria appear on the plate, where each ‘colony’ was started from a single bacterium. Now you know why these are called ‘colony-forming units’ or CFU, in short. We then count all colonies and do some maths. On average, there are over 1.5 billion live bacteria in 1 mL of Quas or over 500 billion CFU per 330 mL of Quas! Check out our Science page to see how it is actually done.

Is kvass safe for pregnant women?

There are two possible concerns regarding kvass and pregnancy: probiotics and low alcoholic content. Probiotics generally do not appear to pose any safety concerns for pregnant and lactating women (Elias et al., 2011). Furthermore, a recent systematic review suggested that probiotics may have the potential to reduce infant allergies when administered prenatally (Colquitt et al., 2022).

Regarding alcohol, the official advice from the NHS is to completely avoid any alcohol during pregnancy. However, recent research funded by The UK Medical Research Council called this recommendation mostly a precautionary principle (Mamluk et al., 2017). The researchers further found limited evidence that light drinking (i.e. 2 UK units of alcohol consumed two times per week) in pregnancy causes negative health outcomes compared to complete avoidance of alcohol. We will let you decide for yourself but will remind you that one 330 mL can of Quas contains about 0.75% (ABV), which is equivalent to 0.25 units of alcohol.

Why does kvass have a dark brown colour?

Traditionally, kvass was made from oven-roasted rye bread. In this case, the dark colour comes from the roasting step. On a larger scale, malted rye grains are roasted instead of bread. This results in a slightly sour flavour of roasted rye breadcrumbs and brown colour that contribute to the unique features of the Original Quas.

Can kvass ease irritable bowel syndrome (IBS) symptoms?

Researchers conducted dozens of randomised controlled trials (RCTs) where probiotics containing a single type (single-strain) or multiple types (multi-strain) of bacteria have been used to improve irritable bowel syndrome (IBS) symptoms. Several recent reviews have independently concluded that probiotics can indeed improve IBS symptoms (Dale et al., 2019; Niu and Xiao, 2020). Researchers agreed that a multi-strain probiotic had greater potential to improve IBS symptoms than a single strain. The best positive effect was also found when the probiotic was consumed regularly for a period of 8 weeks or more. We do not yet know which particular types of bacteria help the IBS symptoms the most, so a product containing a broad spectrum of bacteria, such as genuine kvass, could be a great starting point!

Is kvass isotonic to be used as a post-exercise drink?

Isotonic solutions contain nutrients in the same concentration as the human blood. This property allows our body to quickly absorb both liquids and nutrients from the solution. Interestingly, isotonic solutions will hydrate our body faster than water! To be considered isotonic, the solution must have osmolarity of 270-330 mOsm/kg (De Fusco et al., 2019). The osmolarity of Quas is around 285 mOsm/kg, so our kvass can be called an isotonic drink. However, keep in mind that commercial kvass is a hypertonic solution because of its significantly higher sugar content!


Colony forming units in each can


Raw, unpasteurised, unfiltered


Types of bacteria in each can


No additives, sweeteners, flavourings or stabilisers


Low sugar


Fully plant-based

Ginger Quas

Mint Berry Quas

Mixed Pack Quas

Original Quas