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What is Mold and How Do I Do I Prevent It? 

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Mold… sometimes it’s good, and sometimes it’s bad. Though blue cheese and aged beef can be delicious, when it comes to Kombucha, stay the heck away! While Raw Brewing Co. cultures are the strongest on the market (and can take a lot of abuse), if you aren’t a little careful, this uninvited guest has the potential to wreak havoc on your brew. So… just what is mold, and how can it form on kombucha?

Mold is a fungus that grows on decaying matter and requires moisture to produce and spread. There are different kinds of molds, but the mold that can appear in your kombucha brew is comparable to what would be found on old fruits, veggies, and bread. But, unlike other lifeless drinks or old fruits and veggies, there’s nothing dead about Kombucha. To make kombucha, there needs to be life– bacteria, yeast, oxygen, warmth, and time.  And the three most important things you need to control to prevent the potential for moldy booch are cleanliness, starting pH, and temperature.


First, keep that kitchen and all your booch gear clean, alright? For more information on what to use for your brewing, and how to keep it clean, see Kombucha Equipment and Cleanliness.

Remember how to properly cover your brew while it is fermenting. It needs oxygen to ferment, so you can’t cover it with a sealed lid. Coffee filters work well to help keep out the smallest of unwanted things like fruit flies, mold spores, and wild yeasts. However, a good cover is no substitute for good booch hygiene. You still need to maintain a clean working space in order to produce the best brew and healthiest culture. 

Starting pH

It is crucial that your brew doesn’t have a chance to form mold. As important as temperature (and maybe more so), a key factor in preventing mold forming is getting the starting pH right.  Without the right pH, your brew is unable to fend off the unwanted invaders (i.e. mold spores).   Your starting pH should be between 4-4.5, and keep in mind that the pH will drop through the first fermentation process. The correct starting pH will prevent growths by creating an environment with an acidity level mold can’t handle. Starting close to or at 4.5 (but never above 4.5) is the best for your brew, so it doesn’t drop too low during fermentation and end up too sour. Dropping it low is great for the club, but keep it out of the kombucha process if you want the best tasting booch! When you’re finished with the first fermentation, the pH should be around 3.  For more information on kombucha and pH, see Kombucha and pH.


The fermentation process works best in temperatures between 74-84 degrees Fahrenheit. Temperatures below 70 degrees are not suitable for kombucha production, as they vastly increase the chance of mold (and take too long to ferment, anyway).  The warmer your brew (to around 85-90 degrees), the faster it will ferment and the healthier your SCOBY will be.

The success of your brew depends on the environment and whether or not it’s what your kombucha needs. If it’s not, this may cause molding in your brew. A common mistake for new brewers is to leave their batch in an area that’s too cold. Cold temperatures mean the yeast and bacteria in the culture won’t be very active, and won’t be reproducing quickly enough to further drop the pH, consume the sugar, and protect the brew from potential invaders.  Weak starter liquid can mean the same…because you are starting with such a low bacteria and yeast count.  Inactive, underactive, or weak cultures give mold the chance it’s looking for. You know what they say, “when the kombucha cat’s away the moldy mice come to play.” Or… something like that.

What does it look like?

It’s understandable if it is difficult to discern what is and what isn’t mold in your brew. Things to keep an eye out for are the following: fuzziness in texture, or discoloration like blue, white, black, and green. Also, mold will often grow in spots or circular patterns.

Things that are natural in kombucha that can be mistaken for mold can be the following: carbonation bubbles, new pellicle babies growing, bits of yeast, or tea sediment. If you still aren’t sure if it is or isn’t mold, then don’t worry! Submit a clear photo of your brew to our Kombucha Diagnosis Forum. At RBC, we got you (and your SCOBY’s) back.

How to prevent it

    • Keep your workspace and working materials clean.
    • Make sure you have a low enough starting pH. Never start your brew above a pH of 4.5.
    • Keep your brew in an area between 74-84 degrees Fahrenheit.  Do not put your brew in the fridge or in the sun.
    • Keep your brew covered (with something breathable).  We recommend coffee filters. 

Pretty simple, right?  Basically…just don’t totally neglect your brew! And when you start brewing, start with a strong starter like Gaia. Strong, highly active starters (like Gaia and Honey) will finish your brew faster– and exponentially reduce the chance of mold. 

On the off chance your brew does mold, throw it out, and start new. Sorry, but there’s no reviving a moldy booch.  And while drinking it won’t necessarily kill you, it probably won’t taste very good and could make you sick. Don’t do it… not even for a dare, okay? 

And always remember that your booch is alive. If you let Mother down, we can’t promise she won’t try to seek revenge from the afterlife! Happy brewing, booches!


“CDC – Mold – General Information – Basic Facts.” Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, August 11, 2020. https://www.cdc.gov/mold/faqs.htm.

“What Are Molds?” EPA. Environmental Protection Agency, February 21, 2017. https://www.epa.gov/mold/what-are-molds.

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