Got mold on second batch. What happened?

[KombuchaLA]

My first ever batch was a success. I used a kit I bought from amazon along with a new gallon jug.

From that batch, I got a new, but not fully formed SCOBY.

For the second batch, I brewed rooibos tea and put in the new SCOBY after it cooled. Two days later I see mold spots growing on the top and the SCOBY is at the bottom. It never floated to the top as I thought it would.

This is the process I took to transfer the SCOBY to the tea. I did mess up a bit in the process, but I want to know where things got contaminated.

0. Cleaned hands
1. Brewed tea in the jar. Let it seep for about 5-7 min
2. Used clean tongs to take out tea leaves, which were in a large tea bag
3. Let tea cool overnight, covered with tissue and rubber band. Meanwhile, first batch with new SCOBY is in original jar in about 2 cups of it's original juice (I bottled the rest)
4. Next day, I realized I forgot to put in sugar. I put a cup of sugar in a bowl with a little bit of hot water and mixed with single, clean chopstick. Poured it into tea and mixed with chopstick.
5. Cleaned hands, took out SCOBY with bare hand and placed into the jar. Covered with tissue and rubber band and placed in closet.

Where did I go wrong and what should I do to minimize contamination risk next time? Thank you!

 

[gnomebrew]

A couple of things, I think:

The culture didn't have the proper nutrients to feed it, and allowed mold the chance to hop into the brew. Kombucha really needs Tea, as in Camellia sinensis: black tea, green tea, or oolong (maybe some others too, I don't recall). You can use rooibos for flavoring after fermentation. Actually you could probably add it to the primary ferment, so long as you have enough black tea to support the culture.

Also, the late sugar addition would have prevented the Kombucha cultures from getting off to a good start before other things invaded.

I think for a gallon batch you may want to hold back a little more Kombucha from the batch. I don't really ever measure, I just eyeball about 10-20% of the container and hold that much back. It's more than two cups though. That should keep a good enough acid balance to prevent riff raff like mold from easily hopping in.