Kvass: The breakfast of champions

Yesterday morning, as I waited in the dark at a bus stop at 7 a.m. for the bus to take me to Riga, a watery-eyed guy emerged from a side street carrying a hedge cutter and backpack. He then pulled out a 2-liter bottle of kvass, took a mighty swig, and held the bottle to me and an elderly man who was standing by me. The elderly man took a drink, but I politely declined with a "Ne, paldies." I then asked, "brokastis?", but he didn't understand my accent and held the bottle to me again. I still refused, but had never thought of kvass as a breakfast drink before.