Real talk: Mold
Mold is probably one of the most common fears
home brewers have. But honestly, as long as you’re brewing
kombucha properly (and this site will teach you how!), then
the likelihood of you encountering mold is super, super low.
Below, I’ll go into detail about why mold fears are
exaggerated, how you can prevent mold and what you can
do in the rare instance that you do encounter mold.
You can click these links to jump straight to the topics
below, or you can just keep scrolling to get to 'em all:
Should I be afraid of mold?
In short, no. There’s no reason to be afraid!
Firstly, like I said, mold is super unlikely if you’ve got a good understanding of how kombucha works and you take the steps to do it right.
Secondly, in the rare instance that you do encounter mold, it’s really not as big of a deal as a lot of brewers tend to make it — it’s not any more harmful than mold that grows on old bread or fruit that’s past its prime. I think a lot of people worry that kombucha mold is somehow more “poisonous” than other food mold, so they amp up the drama or the fear accordingly.
Real talk: It’s not. If you get a moldy piece of bread in your kitchen, you just throw it out. You don’t freak out, right? Same goes for kombucha. So unless you have a deathly mold allergy, you don’t need to worry.
Home brewers’ fears are also probably amplified by the fact that kombucha-making is a bit of a gnarly process. There’s a weird-looking SCOBY involved, and funny-looking yeasty bits can grow throughout the process. They don’t always look the same as others’ kombucha brews. It’s not always pretty. (You’ll grow to love it over time, trust me.) But if you’re not sure what to expect, it can be a little daunting.
I will tell you, though, that more often than not, it’s not mold. You should always pay attention to your brew, and you should be aware of the telltale signs of mold, but you should definitely not fear mold!
How do I prevent mold?
The main way to prevent mold is to make sure you’re brewing kombucha properly. This site can walk you through all the info you need and more to make sure you have a solid understanding of how kombucha works. Oftentimes, when people encounter mold, it’s because something in their brewing process isn’t ideal — and it may or may not be their fault.
But here are some precautions you can take to prevent mold:
Use a good amount of starter tea to acidify your brew. The starter tea helps bring the pH down to a low enough level where mold can’t thrive. (But do not use vinegar. Vinegar is not necessary and harmful to kombucha.) I like to use at least 2 cups of starter tea per gallon batch. Learn more about pH's role in the fermentation process here.
Don’t refrigerate your SCOBY, starter tea or brewing vessel. Temperatures below 65 degrees make the yeasts and bacteria go dormant. If they’re asleep, they can’t get the fermentation process going to acidify the brew. If they can’t acidify the brew, the kombucha will be more susceptible to harmful mold and pathogens. Mid- to high-70s is the ideal temperature for kombucha, so keep it somewhere as close to that range as possible. Read more about temperature control here.
Don’t keep your brewing vessel in a moist area with poor air circulation. Or anywhere there might be mold, like near your fruit basket or near house plants. Read more about ideal brewing locations here.
Fully strain your tea. If too many solid tea dregs or other particles get into your brew vessel with your SCOBY, it could attract mold.
Use the right kind of tea and sugar for your brew. It’s also worth saying that you shouldn’t let flavorings or oils (even natural ones) come into contact with your SCOBY or your first ferment. Experimenting with different types of teas during first fermentation can be really fun as long as know what you’re doing and have back-ups in case the unthinkable happens. But if you use a tea with flavorings...or use herbal teas/something other than real tea (camellia sinensis)...or if you use something other than cane sugar, then you could be starving the yeast and bacteria in your brew. Kombucha cultures best feed on pure tea (black tea is best) and cane sugar. It may not be able to eat the experimental ingredients you feed it with. If it starves, then it can’t do its job and acidify the brew. If it can’t acidify the brew, then mold can move in and set up shop in your kombucha. Learn more about the best tea and the best sugar for your kombucha.
Note: Kombucha “sins” like the ones I outlined above can also degrade/weaken your SCOBY over time. So for example, if you tried to first ferment with chamomile or earl gray a few batches ago and it turned out fine, that may not be the case forever. It could be going great until suddenly it’s not. And you may wonder what the cause of it was.
Sometimes, the cause of unexpected mold can be actions that took place a few kombucha SCOBY “generations” or batches ago.
Can mold happen in the bottle?
If you’ve been able to produce a successful batch of first fermented kombucha and you’ve gone over a week without any mold in your brew vessel, it’s very unlikely that you’ll develop mold during second fermentation in the bottle. I’ve actually never heard of this ever happening. Assuming you’ve gone through a successful first fermentation cycle (read here to know what to look out for), then the pH of your kombucha will have dropped to a point that makes it inhospitable to mold.
So you really only run the risk of mold during F1. If you made it past that successfully, then barring some really crazy circumstances, you’re pretty much in the clear.
What does mold look like?
You should definitely be aware of what to look out for just in case. It’ll usually look like what you expect mold to look like— if you’ve ever encountered a moldy piece of bread or cheese or fruit, it’ll usually look very similar to that.
Mold is fuzzy.
Mold always grows on the surface. Mold cannot survive in anaerobic environments.
Translation: it needs air to thrive. So don’t mistake brown stringy yeast or bits of tea for mold.
Concentric circles. Mold doesn’t always take the form of concentric circles, but they very often do.
Mold can be white, green, black, blue, red...if you’re seeing interesting bright colors, that’s a bad sign. SCOBYs are usually white/cream to brown in color, but fuzzy, snowy white is bad, especially if it’s a layer on top of your brew vessel.
Below are a few examples of mold. This isn't totally inclusive by any means! If you have photos of your SCOBY mold you want to send me to add to the mold gallery, send 'em here!
As a point of comparison, go here if you want to see a collection of healthy but "weird-looking" SCOBYs.
What if I’m not sure if it’s mold?
Kombucha can be a weird-looking process. Read here to find out more about what to expect during first fermentation and to read about what a healthy brew looks like.
If you really, really can’t tell, I suggest waiting it out for at least a few more days. Isolate it from your other vessels and away from your kitchen and just wait.
Sometimes, when a new SCOBY is trying to form, it can look like mold, but after a few days, once the disparate SCOBY parts all come together, you’ll realize it’s actually a healthy brew.
Sometimes yeast can turn a really dark color and can even look circular in shape, but if it’s not on the surface of the vessel and it’s not fuzzy, it’s probably not mold.
If you’ve waited 5-6 days, it should be easier to tell at that point if it’s mold or not. Because at that point, it’ll just look moldier.
OK, OK, so you keep telling me not to worry about mold, but I GOT MOLD. Now what?
My condolences. I know it can be disheartening, but it does happen occasionally.
In this case, you should throw away your SCOBY and any liquid that it has come into contact with. Do not ingest any of it or try to “save” it. A moldy brew is a lost cause, unfortunately. You cannot salvage a SCOBY that’s already been infected with mold.
Clean and sanitize/sterilize all equipment that’s come in contact with your kombucha and start over with a new SCOBY and new starter tea. Beer brewers are likely familiar with Io Star or a similar iodine-based sanitizer. You can certainly use that.
If you know what caused the mold to happen, now you can take steps to prevent it from happening in the future. If you’re not sure, then take some time to poke around this site or watch my videos. It’s a learning process for all of us. You can always start again and get right back to brewing kombucha, so don’t give up!
Fuzzy, circular mold on surface of liquid.
Red concentric circle mold on top of scoby.
Fuzzy, circular mold on surface of liquid.
Fuzzy, snowy white mold spores across top of scoby.