When you make kombucha, the starter SCOBY, or mushroom, replicates itself much like a vinegar mother. This new mushroom baby can be given to a friend or used to start another wonderful batch of kombucha. But how on earth do you start making kombucha without a mushroom or kombucha-brewing friends??
Here's the secret: you can grow your own SCOBY with nothing but some kombucha! It takes a few weeks to grow, but it's so easy there is no reason to buy a mushroom.
When you first start using small orphan SCOBYs, the kombucha will be a little weak. Give it some more time to grow. As anyone who has over-brewed kombucha knows, those mushrooms can get really, really big. And yes, they can still be used at that size (just peel it into smaller parts... otherwise it won't fit in the next brewing jar).
I'm not sure if store-bought 'bucha can replicate like this because I never buy kombucha. But it should, right? Somebody out there should give it a try. :)