Either use stale bread or toast the bread before cutting into large cubes.
Place into a large sterilised jar with the remaining ingredients. Give it a good stir.
Loosely cover with paper or paper towel, or even a piece of cheesecloth and secure with an elastic band. Sit on the bench out of direct light for 2-3 days before checking the flavours and fizziness.
Initial Fermentation:
After toasting the bread, soaking it in water, and adding a starter (like sourdough starter), the mixture will begin to ferment.
Visible Signs:
Within 2-3 days, you should see bubbling and movement in the liquid, especially if kept at a warm room temperature. The bread will also likely shrink in volume.
Taste Test:
Begin tasting the kvass after 3 days. The taste will change as the fermentation progresses, becoming more sour and less sweet.
Monitoring:
You can stir the mixture once a day and burp any pressure that builds up, especially if using a sealed container.
Ready for Strain and Bottle:
Once the kvass reaches your preferred level of tartness, you can strain out the bread solids and bottle it, optionally adding raisins for further carbonation.
Re-Fermentation (Bottling):
After the initial fermentation, the kvass is bottled, often with additional raisins or other flavourings.
The bottled kvass is usually kept at room temperature for a day or two, and then chilled in the refrigerator.
The longer it ferments in the bottle, the more carbonated it will become, and the more alcohol it will develop (though still usually low, around 0.5-2%).
Burping:
During both the initial and secondary fermentation, it's important to burp the bottles (release excess CO2) to prevent explosions, especially when using glass bottles.
Safety:
Plastic bottles are often preferred for secondary fermentation due to safety reasons, as they allow you to gauge the pressure build-up.
Flavour:
The longer the fermentation, the more the flavour will develop, potentially becoming more sour and yeasty.
Add fresh mint, sliced apple, berries, raisins, or even lemon peel to change it up.
It will be ready to drink after 3 days in the fridge. However, it will continue to ferment for another 1-2 weeks until all the sugars have been consumed by the yeast. At that point, it will no longer be sweet and it will have developed some alcohol content. I recommend drinking it within the first 3 to 7 days for the best flavour. Having said that, we made it in August 2025 and as of January 2026 we are still drinking it, and I may even like it more than I first thought!