Short answers, pulled from the story.
The word kvass traces its roots to the Proto-Indo-European base *kwh₂et-, meaning 'to become sour'. This linguistic lineage connects the modern Slavic drink to ancient concepts of fermentation and acidity. The first written mention appears in the Primary Chronicle describing Vladimir the Great's baptism in 988.
Home fermentation begins with dried rye bread or a combination of rye flour and rye malt soaked in hot water. The mixture incubates for 12 hours at room temperature before bread yeast and sugar are added. A second fermentation period follows, lasting another 12 hours at the same ambient temperature.
Commercial production began in earnest during the second half of the 19th century alongside military engagement and large-scale projects like the Trans-Siberian Railway. By the year ended the 30th of June 1912, seventeen factories in the Governorate of Livonia produced a total of 437,255 gallons of kvass.
Alcohol by volume usually does not exceed 1.5%, though it can reach as high as 2.0% depending on ingredients. Naturally fermented kvass contains 5.9%±0.02 carbohydrates, of which 5.7%±0.02 are sugars mostly fructose, glucose, and maltose.
Coca-Cola launched its own brand of kvass in May 2008 marking the first appreciable entrance by a foreign company into the market. This occurred after the Russian company Nikola promoted its brand with an advertising campaign emphasizing anti-cola-nisation while per capita consumption reached three litres that same year.