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What is Mold and How Do I Prevent It?

Mold: depending on the application, it can be a culinary dream or a brewing nightmare. While it's the secret behind the unique flavors of blue cheese and aged beef, it's a definite no-go in the world of kombucha brewing. Despite the robust nature of Raw Brewing Co. cultures, mold can still find its way into your brew if you're not careful. So, what exactly is mold, and how does it find its way into a kombucha brew?

Mold is a type of fungus that thrives in moist environments, often found on decaying organic matter such as old fruits, vegetables, and bread. Unlike these, kombucha is a vibrant ecosystem teeming with life, thanks to the presence of bacteria, yeast, oxygen, warmth, and time. To ensure a mold-free brew, focus on three pivotal factors: cleanliness, starting pH, and temperature.


  1. Maintaining a proper environment is your first line of defense against mold, and it is paramount. Ensure your kitchen and brewing equipment are clean.

  2. While it is essential to cover your brew with a breathable cover during fermentation to allow oxygen in, and to keep out the smallest of unwanted elements like fruit flies, mold spores, and wild yeasts.  Your brew needs to breathe during fermentation, so a sealed lid is no-go. What's the best cover? We wrote a whole article about it here

  3. Remember, a proper cover like a coffee filter can help keep out unwanted elements, but it's no substitute for proper hygiene and equipment. A clean environment fosters a healthy culture, setting the stage for a perfect brew.
  4. Dive deeper into the best practices in our detailed guide on

    Kombucha Equipment and Cleanliness.

Starting pH

Starting at the right pH is a critical step in safeguarding your brew against mold -- it is as important as temperature (and maybe more so). Without the right pH, your brew is less able to fend off the unwanted invaders (i.e. mold spores).  Whereas starting at the correct pH will prevent growths by creating an environment with an acidity level mold that is hostile to mold spores.

The ideal pH range is between 4 and 4.5, creating an acidic environment  As fermentation progresses, the pH will naturally decrease, enhancing the brew's flavor without becoming overly sour.  But remember, don't start too low, because we don't want your brew to be too sour when it finishes.  Dropping it low is great for the club, but keep it out of the kombucha process if you want the best tasting booch! 

Bottom line is this: most commercial kombucha brewers start at a pH of 4 and finish at 3. Learn more about the intricate role of pH in kombucha brewing in our insightful article, Kombucha and pH


The temperature sweet spot for kombucha fermentation lies between 74-84°F. Temperatures below 74°F not only prolong the fermentation process but also vastly elevate the risk of mold invasion. A warmer environment, up to around 84°F, accelerates fermentation, promoting a healthier SCOBY.  Avoid cold spots and ensure a consistent temperature to foster active yeast and bacteria, essential in lowering the pH and consuming sugar, thereby shielding the brew from potential threats.

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 chilly. 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 sugars, and protect the brew from potential invaders. 

And weak (or not enough) starter liquid -- or not including a pellicle from a previous brew -- can mean the same.  In this case, you would be starting with a low bacteria and yeast count that can't keep up.  Inactive, under-active, 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.

Identifying Mold

It’s understandable if it is difficult to discern what is and what isn’t mold in your brew. Identifying mold can sometimes be a tricky endeavor, especially for new brewers. Mold may appear as fuzzy textures or exhibit colors such as blue, white, black, or green, often forming in distinct spots or circular patterns. It is essential not to confuse these with natural occurrences in kombucha like carbonation bubbles, new pellicle growth, or tea sediment. 

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 find yourself in a dilemma, our Is it Mold page is here to assist you.  At RBC, we got you (and your SCOBY’s) back.

Prevention Tips

  • Workspace: Keep it clean and organized to prevent any mold spores from finding a home in your brew.
  • Starting pH: Ensure it is no higher than 4.5 to create an environment hostile to mold.
  • Temperature: Maintain a range between 74-84°F to facilitate optimal fermentation.
  • Cover: Use breathable materials such as coffee filters to cover your brew, preventing contaminants while allowing necessary airflow.

Pretty simple, right?  Embarking on the kombucha brewing journey is an exciting endeavor.  With a robust starter like Gaia, you can significantly mitigate the risk of mold, ensuring a delightful brewing experience. Strong, highly active starters will also finish your brew faster. In the unfortunate event of a mold outbreak, it is best to discard the batch and start anew. Sorry, but there’s no reviving a moldy booch.  Remember, the vibrant world of kombucha is alive, and nurturing it well promises a rewarding, flavorful yield. Happy brewing, booches!


“CDC - Mold - General Information - Basic Facts.” Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, August 11, 2020. “What Are Molds?” EPA. Environmental Protection Agency, February 21, 2017.

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