If beetroot is organic, you don't have to peel the skin. Just spray some vinegar and scrub the dirt off well.
Cut up beetroots in small squares for faster fermenting. But DO NOT shred or grate it as they will ferment too quickly and turn into alcohol. Well, if that's what you want, I guess you can but for probiotic purpose, you don't want to grate it.
Add beet to the jar. Fill up the jar with filtered water, leaving about 2 inches at the top.
Leave the jar on the counter for about 2-5 days. Taste to your liking and keep it refrigerated.
When you have a little bit of kvass left in the jar, you can make a second ferment...or third...until beetroot looks pale. Then, they are spent and you'll have to start a new batch.
You can dilute with water or carbonated water or straight up or add it to your juicing or blending. And add some ice and ENJOY!