Fermenting Kvass: A Slavic Bread-Based Ale

When starting my co-op at Escarpment Labs it was recommended that I devise a project involving fermentation. I decided to try making kvass, a beverage my parents enjoy, but I had never tried. Despite my parents being from Eastern Europe, they hadn’t had kvass before moving to Canada, hence their taste for kvass developed. Kvass is a mildly alcoholic fermented drink (0.5-2.5%) traditionally made using stale rye bread, yeast, sugar, and dried fruits for flavouring; it has a sweet/sour taste. After spending months brewing kvass I have grown to enjoy it in all its iterations. 

Getting Started with Kvass

The general brewing of kvass involves steeping toasted stale or dry bread in water, then draining the liquid into a fermentation container. Yeast and sugar are added and the mixture is left to ferment. 

I went through 3 rounds of making kvass. The first was to try out a recipe and do some troubleshooting, the second was to try making kvass using different types of yeast, and the third round was an exploration of flavouring the kvass with fruits, herbs, and spices. 

I searched the internet for kvass recipes until I found one that offered clear instructions (the original recipe I followed) and then altered the recipe to better suit the yeast and supplies I was using/had access to. I also used a recipe to make the sourdough rye for the kvass. (Note: By no means do you have to make your own bread for the sole purpose of making kvass, but you can if you want to!) 

Round 1: Finding a Recipe

For the first round of kvass brewing I used homemade rye, which I toasted in the oven. The rye bread used became a standard amongst all trials, however stale bread is preferred to minimize waste. I also used homemade sourdough starter as the yeast along with granulated white sugar which was added after soaking the bread. In order to ensure fermentation was occurring, I checked the gravity of the kvass every other day. It is here I learned that unlike beer, kvass does not reach a stable gravity, and will continue to ferment. So an important takeaway is that once the kvass hits your desired gravity transfer the container to the fridge

Round 2: Finding a Yeast Strain

For the second round of kvass brewing I made four different kvasses using different yeasts and bacteria. I had made the same base as the previous trial, however I used less sugar (to minimize over fermentation) and dissolved the sugar in 150 mL of warm water before being added to the bread infused water. 

The strains of yeast that I used were Voss kveik, Finnish Sahti, and the same homemade sourdough starter. I also made a fourth kvass that combined Voss and lactobacillus plantarum to create a “sour” kvass. For the sour kvass I had pitched the lactobacillus without the yeast and allowed the bacteria to grow for 3 days (this ended up being a bit too much), measuring the pH each day to ensure it was dropping. Using the knowledge I had gained from the first trial I had checked the specific gravity each day and used an ABV calculator to determine the alcohol content of the kvass, then put them into the fridge when they reached the desired percent. 

The kvass was left for two days in the fridge until I poured off the liquid into growlers. I ran a sensory on the finished product, all were generally on the flatter side of carbonation, refreshing, and the (bit too) “sour” kvass was the clear favourite.

Round 3: Finding the Flavour

For the third round of kvass brewing I made 5 flavoured kvasses. After brainstorming some flavour combinations and using knowledge I had gained from the last two trials, I chose to make:

  • An orange peel, ginger Sahti kvass 
  • A lime peel lacto/Voss kvass
  • A dried cherry lacto/Voss kvass
  • An apple Sahti kvass
  • A rosewater, raspberry Voss kvass

I repeated the same process making the previous kvasses, adding the fruits and flavourings along with the yeast and sugar. Checking the gravity everyday, I put the kvass into the fridge earlier to allow them to ferment more in their final containers and increase carbonation. I decided to use different containers for serving the kvass and purged them with CO2 before transferring the settled kvass. I then left them to sit at room temperature for another 2 days to ferment some more. I again encountered problems with carbonation, apart from the rosewater, raspberry kvass, so adding more sugar or adding it during secondary fermentation might also help (if adding more sugar, there is the chance that it over-carbonates).

Finally, I ran a sensory on the flavoured kvass, and the rosewater raspberry kvass was the favourite. It received high scores on the sensory for sweetness and aroma, and had the highest scores for fruitiness and carbonation. Check out the interactive graphs below (made by our resident Data Scientist, Hana Knill) to view results from this sensory!

This interactive graph displays the ranking of preferred flavour combinations. Hover your mouse over each percentage to see the name, vote count, and flavours identified. You can click the strains in the legend to add or remove from the graph itself.


This interactive graph displays the most frequent sensory notes. You can click the strains in the legend to add or remove from the graph itself to interpret the results.

Recipe for Rosewater Raspberry Kvass


  • 1 lb of bread (rye recommended)
  • 3 litres of water 
  • ½ cup of sugar (100 grams)
  • 15 mL of yeast slurry (Voss Kveik recommended) or 1 Tbsp sourdough starter
  • ½ teaspoon rosewater combined with 80 g frozen raspberries

* Given that process involves live yeast it is best practice to avoid contamination in any way possible, using sanitizers, clean and or sterile equipment and working in a clean environment.


  1. Cut bread into crouton sized cubes, toast them in the oven at 350 degrees Fahrenheit for around 20 mins, toss half way through to brown evenly or toast to your liking in a pan on the stove.
  2. Place bread cubes into a bowl, jar or vessel of your choice. Bring 3L of water to a boil, then pour over the bread. Let soak for min 4 hours, max 24 hours.  (To measure three litres of water, I placed the jar onto a scale and poured until the scale read 3 kilograms)
  3. Strain steeped bread water into a suitable fermentation container using a strainer or funnel lined with cheesecloth or hop bags that have been soaked in PAA or sterilized in some other method, wring out the soaked bread.
  4. Weigh 100 grams of sugar and allow to dissolve into 150 mL of warm water. Stir yeast and sugar into the strained liquid, add ½ teaspoon and 80 grams frozen raspberries (individually flash frozen raspberries are useful for weighing) 
  5. Leave to ferment in a warm location for around 1 week. If you can check the gravity of the kvass, do so, and allow the gravity to drop until final ABV is between 0.5 and 2% 
  6. Place into the fridge when desired gravity is reached. The sediment will settle after 2 days minimum. 
  7. Decant kvass into sterile growlers or other pressure proof containers of your choosing and allow to sit at room temperature for an additional 2 days. Put the kvass back into the fridge to allow it to cool and enjoy.

*If desired, flavourings can be omitted from this recipe 

*If you want to add lacto to “sour” your kvass add 15mL of the lactobacillus of your choice, allow bacteria to lower pH of solution to desired pH (1-2 days worked for me)

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