Because we counted them! We regularly take samples of Quas for analysis to make sure our kvass is of the highest quality. Part of the process includes counting the number of live bacteria present in 1 mL of Quas. Because there are so many bacteria in Quas, we first need to dilute it to be able to count the bacteria. After diluting Quas 1 million times (!), we transfer tiny droplets of diluted Quas onto a petri dish containing special growth media. A few days later, separate ‘colonies’ of bacteria appear on the plate, where each ‘colony’ was started from a single bacterium. Now you know why these are called ‘colony-forming units’ or CFU, in short. We then count all colonies and do some maths. On average, there are over 1.5 billion live bacteria in 1 mL of Quas or over 500 billion CFU per 330 mL of Quas! Check out our Science page to see how it is actually done.