Short answers, pulled from the story.
Kvass is traditionally made from dried rye bread or rye flour and malt, soaked in hot water and fermented with bread yeast and sugar for around 12 hours at room temperature. Industrial versions use a wort concentrate blended with sugar and water, then fermented with baker's yeast and lactic acid bacteria for 12-24 hours.
Kvass is usually 0.5-1.0 percent alcohol by weight, though it can sometimes reach as high as 2.0 percent. Latvian law caps kvass at a maximum ABV of 1.2 percent.
The first written mention of kvass appears in the Primary Chronicle, describing the baptism celebration of Vladimir the Great in 988, when kvass was distributed alongside mead and food to the citizens of Kiev.
Kali is the Estonian name for kvass, while gira is the Lithuanian name for the same type of fermented bread drink. These are non-cognates, meaning they do not share the Slavic root of the word kvass, though the beverages are closely related.
In 1998, Latvian kvass producers began selling bottled kvass at roughly half the price of Coca-Cola. Within three years, kvass captured as much as 30 percent of Latvia's soft drink market, while Coca-Cola's share fell from 65 percent to 44 percent. Coca-Cola reported losses in Latvia of about one million dollars each in 1999 and 2000, and eventually responded by purchasing kvass manufacturers.
Kvass appears in two well-known Russian expressions. One, perebivatsa s khleba na kvas, means to live from hand to mouth. The other, kvassnoj patriotizm, was coined by the poet Pyotr Vyazemsky in an 1823 letter and means unqualified praise of everything one considers their own, a term for uncritical nationalism.