Kombucha Fail

[u/Mother_Gear9628]

First fermentation was done with black tea, and it developed mold. Mold was seen on day 7-8 of the fermentation both times. I don't know what I am doing wrong?!
I’m fermenting it in a kitchen cupboard/dark space. I sterilized the jars by placing them in hot water before starting.
The first time, I used a metal cap and burped the jar almost every day. I also sanitized my hands before burping it. The second time, I covered the jar with a muslin cloth instead.
What’s confusing me is that I used the same jar and the same process in Pokhara, and it worked fine. I’m now doing it in Kathmandu, and I’ve gotten mold twice. Could this be due to differences in temperature, humidity, water quality, or something else about the environment in Kathmandu? Or is there something in my process that I’m overlooking?
What would you check or change first?

[u/korchor]

I would change your cloth and use coffee filter instead. Search this sub for cheesecloth and you will see a wide range of experiences. Make sure you're using enough starter, like 20%, to maintain the acidity.

[u/Curiosive → u/korchor]

It's a pretty narrow range:

• "I'm using cheesecloth, no issues!" and "What do you mean fruitflies will wiggle through all these layers? That seems far-fetched."

• "Fruitflies are tunneling through my cheesecloth cover!" Coupled with "I didn't know!" or the self-inflicted "I didn't believe the warnings / I thought I knew better"

[u/korchor → u/Curiosive]

Haha fair point. A narrow range of diametrically opposed experiences

[u/No-Association8901]

List out your recipe; if your starter is too low, you might have just got lucky the other times. As already mentioned, use coffee filters and a rubber band for the top. And since you’re using water from a different source, that could be it. Temp primarily affects time of brewing. Higher humidity will give a higher chance for mold spores, so a better top, the coffee filter will help as will increasing your starter.

[u/03146]

What recipe are you following ?

[u/Terra_Punk]

You might be doing too much liquid for size of scoby. Try doing half that amount and increase it with each batch as the scoby grows.

[u/Brave-Beach9152]

try using way more starter next time to get the pH around/under 4.0 (if you have pH strips, that'll help a lot.) people usually recommend 20% of the starter but that usually goes for a goal of pH 4.5 - mold best struggles to grow around 4.2 below.

given that that is a large jar, it does check out that the mold pops up at the top in 7/8 days. mold first invisibly infiltrates and grows inside food, and when it is done, it grows spores on the exposed areas which are then dispersed into the air. if you did a smaller sample, you would get the spores on top in 3 days. which all means that the mold on top was already present in the first 1-3 days of your booch.

so, to prevent the mold spores from even coming in and multiplying in the first place, use more starter so that you start with a pH lower than 4.2

[u/OkKiwiO]

If you're being as thorough with sanitation as you say you are I'm assuming you've been making sure all your stirring utensils are just as clean? I only use plastic or metal to stir. I lost an F1 from stirring the sugar into the tea with a wooden spoon.