Put all ingredients in mason jar.
Add lid and gently shake to mix
Leave on the counter
Check daily. Crack the lid. Taste for fizziness and flavor. Depending on heat in house, it can take 2-7 days to fully ferment. (Be careful with highly fermentable fruits like pomegranate or ginger.)
When it reaches your preferred level of fermentation, filter out the fruit using a sieve or cheesecloth. Save fruit to add to smoothies later.
Serve kvass over ice.