It looks like dark beer but is so low in alcohol that is considered acceptable for consumption by children (but in Russia children also drink highly-differentiated drinks, like milk from radioactive farms and etc). Though sometimes Kvas is thought of as “children’s beer”, it is favored by all ages equally.
In strength, Kvas can be almost alcohol-free and at its strongest is only around 1-1.5% (but even tha air in Russia is saturated around 1-1.5% alcohol..especially the metro). It is often flavoured with fruits or herbs such as strawberries or mint...or anything to tarnish the taste of the chemicals added to make it look natural.
Russians also use kvas for cooking a special summer cold soup, Okroshka (which is rather easy to make: just chop what you can find in the fridge into a bowl of Kvas (but leave aside the green and glowing fungus that takes habitat in fridges made in Ukraine after Chernobyl..actually my old fridge was a farm for itself. I have counted 4 different species living in absolute biological peace)
The most delicious Kvas is sold on the street in unused petrol barrels: Don't miss the hint of siberian premium gasoline taste in your Kvas. (Actually this photo was made in Ukraine... The petrols barrels are always full in Russia: They have to sell more petrol to satisfy their greed for luxury)
The funny thing which I have realised was the sales percentage of the dominant and worldwiode enjoyed brands like Coca-Cola or Pepsi. Russian people (hopefully) have a taste for something more natural and prefer Fruit Juices, Kvas and Vodka. So the overpaid intelligent minds have made some market studies and found out that the "Kvas Market in Russia" reached US$215 million and will be growing 10-15% over next few years...and bad news: The Coca-Cola Kvas (i eagerly wait for the brandname) is soon to be on the shelves...