(I tried to search for an answer to this; while there are numerous questions about Kombucha, I was unable to find the answer).
I thought perhaps it stated this so the stuff at the bottom wouldn't get mixed in. Though I have yet to see a definitive answer online, I'm going to guess Kombucha, since it is fermented, is actually bubbly? Will it explode out of a new bottle if shaken before opening?
The one bottle of Kombucha that I bought from Whole Foods wasn't bubbly...Then again I didn't shake it up, either, before opening. I use it a bit at a time, to mix in with my smoothies.
Yes, it says on the bottle it has natural effervescence. If you shake it, it bubbles over. And that's a not-so-fun waste of an expensive drink :p
Same reason you do not shake a bottle of coke before you open it. It makes it spew. With Kombucha, there is sediment and people want to break that up. But it is also carbonated, so it will spew out if you shake it then open it. If your previous experience was not bubbly, maybe your next one will be. As a natural product, there is variance from batch to batch.
Yes, it will explode when you open it, and perhaps without you even opening it, if shaken. I find the GT's brand to be less effervescent now that they've re-issued it, though. We used to see it (seemingly) spontaneously burst on the shelves when it had the higher alcohol content due to a longer fermentation phase.
ETA: It's recommended that you gently roll or turn the bottle over slowly to mix the sediment in.
I make my own kombucha - but when I do buy the bottled stuff I open it drink a little then put the lid back on & shake gently. My home made stuff is very carbonated so I only fill my bottles about 3/4 full when I do my second fermentation, otherwise when I open it for the first time it will fizz up & out of the bottle and approx 1/4 of the contents goes down the drain.
You're not supposed to shake it because they don't use a bottle that can hold carbonation like beer or soda (it's more expensive to bottle this way).
Fermentation can continue in raw kombucha even in the refrigerator, raising the alcohol level and CO2 at the same time. So if it's too fizzy it's got more alcohol, and possible much more. This is what got them pulled off the shelf two years ago.
Kombucha doesn't need to be raw because it's not a probiotic drink (much mis-information about that). There are other alternatives like Kombucha Wonder Drink and Clearly Kombucha that won't leak, fizz or make more alcohol.
Like the others answers said, the contents are carbonated (the kombucha yeasts produce the carbon dioxide).
My homemade brew (stored in used GT Dave's bottles) usually has a lot of the dark yeast cultures, which often sink to the bottom. To get some of the solids from the bottle into my glass, I use these steps:
I try to do steps 3 and 4 rather quickly to keep the cultures near the cap.
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