Kombucha, which is similar to the kefir juice I made except that it is fermented tea instead of fermented juice(juice extracts are often added to kombucha it) is now legally considered “beer”. I didn’t realize this until recently. It has been a while since I’ve bought kombucha from the store or even looked at the label. Last time I bought Synergy Kombucha it it was not legally considered “beer”, and you didn’t need to be 21 or older to purchase.
Since the blueberry kefir juice has a similar amount of alcohol(0.5% to 2% max) and maybe more, it is also a “beer”, legally speaking.