That is a good question.
Been seeing those nicely bottled products recently and I remind myself of the fermented tea I left in my fridge for I think ..almost a year.. provided the scoby don't die. What is SCOBY? That is the fungi looking something that got mutated from a jelly fish and a plant that grows in the drink. It's basically a Symbiotic Colony Of Bacteria & Yeast and not the scooby snacks from scooby-doo.
Just an off note, the by product CONTAINS ALCOHOL that is derived from the sugars , similar to a cider and dependent on your usage, I like to make it into more or less a natural balsamic vinegar.
How much it cost? Quite hefty actually... and it can only hold fresh for 2 weeks before it becomes sour... .... I do have mine like I said for a year...did not try it yet....
Lets see later when I post the pics