It turns out that trying to keep things really clean (or even sterile!) isn't going to help much. There's a lot of mold spores everywhere, all the time. Not much chance of keeping it away.
However, you can do a lot to make things unfriendly for molds. They don't grow on really acidic stuff. So the trick with kombucha is to drop the pH as quickly as possible.
Remember that when you make kombucha, it goes like this:
1. Brew strong, sweet tea
2. Cool to body temperature
3. Add a peice of a kombucha "mushroom" and 10-20% fresh kombucha from a previous batch.
The "mushroom" (pancake, sponge, SCOBY, whatever) has the most cultures in it. The previous kombucha is primarily to lower the pH.
I like my kombucha a little sweet. After 5 days, I find it very yummy. I am trying to limit my sugar intake, so I'm more sensitive to sugar than most people (who drink a lot of cola). That also means I want to let it go a little longer, so the culture removes more sugar. I aim for about 7 days.
(I really should taste it every day until it reaches the tartness I like.)
Anyway, one of the tricks for preventing mold is to use a very acidic starter. Let a batch brew for 15 days and it will be very acidic. Hard for most people to drink, but a good substitue for vinegar on a salad.
So I started up 2 batches:
- A large batch (3qts of kombucha in a 4qt bowl). Used distilled vinegar to help lower the pH. After 7 days, drank it & started a new batch.
- A small batch (1qt in a 2qt bowl). Let it go a long time to lower the pH. Will use this for starters only, not for drinking.
Hopefully I'll find a replacement at the thrifts store. Even better, I'll find 2-3 good bowls, and be able to make enough kombucha to share with friends.