Kombucha - What's the Worst Thing That Can Happen? Mold!

By Ariana Estelle-Symons, Ph.D., Copyright 1997
From the Kombucha Konnection Newsletter, April 1997

Kombucha - an unusual name for an unusual sort of brew. Actually, it's not that strange - it's just a little different. In this age of fast foods, microwaves, and quick fixes, it may seem a little out of the ordinary to actually boil water. But, once you get the hang of it, brewing Kombucha Tea is not terribly difficult, nor is it particularly time consuming.

I know that when I obtained my first Kombucha, I was scared to death of it. I was a nervous wreck, thinking that I did not have the proper 'training' to prepare something so exotic as Kombucha. To tell the truth, I had no training - not even a sheet of instructions - and I was pretty much flying by the seat of my pants.

This newsletter is the direct result of that 'lack of training'. I vowed six years ago that no one should have to suffer Kombucha anxiety attacks due to a lack of information. Over the years I've heard some quite bizarre stories about Kombucha, both from the novice and from the 2 or 3 year 'brewing veterans'. Everything from 'the cat fell in the brewing bowl' to 'my wife cleaned the fridge and threw away all my cultures' to 'there's green fuzzy mold all over the baby' to 'nothing is happening, after 10 days, no baby'.

Let's take a look at some of these 'worst case scenarios'.

Undoubtedly the worst fate that can befall the Kombucha brewer... is... MOLD! Why? Because once mold makes it's ugly appearance, you must throw everything away! The baby, the mom, the fermented tea... the works! You can't wash it off, scrape it off, or cut it off.

A couple of weeks ago, a friend in Oregon called telling me he had mold covering his newest baby Kombucha, and he was bewildered. You see, back in January, he had the same problem. So, following the directions of a well meaning friend, he cut off the moldy part, then he washed the baby and the mom in vinegar. Seems as though there's a book out that tells you that this is the way to get rid of mold. Well, everything went along okay for awhile - and then - once again... MOLD. He said that he'd had several batches turn out beautifully - with no mold. I asked him if he had any of these in 'storage'. He said he did, so I asked him to send me one. When it arrived, it looked fine. A pale culture, nice and thick (nearly 1/2 inch). I couldn't see a trace of mold. So, my curious nature prompted me to investigate further. I sliced the culture open - and sure enough - threaded throughout the middle of the culture was a vein of blue/green/black mold. The inside of this colony looked just like 'bleu cheese'. Not apparent on the outside - but there - all the same.

This discovery reminded me of the conversation I'd had with the FDA last year. One of the main reasons they advise people to use extreme caution when brewing Kombucha is that mold can become embedded in the culture/colony (or pellicle as they refer to it). It survives and thrives, sometimes unseen, never noticed until it gets really rambunctious and pops up on the top of a beautiful baby Kombucha.

Okay - what does "Kombucha mold" look like?? Nothing exotic here - it looks just like mold on bread, or fruit or cheese. We've had reports of green mold, black mold, white mold, and gray mold, but regardless of the color - it's always fuzzy.

So - what kind of mold is it? According to Michael Roussin, Director of the Kombucha Consumer Research Group in Salt Lake City, the two most often found molds on Kombucha are: Penicillum notatum and Aspergillus niger. Mr. Roussin's group of researchers tested many hundreds of Kombucha colonies during 1996, and during this time found that these two molds were the two they isolated from the tested colonies. According to them, Penicillum notatum is the green mold and Aspergillus niger is commonly white, black or gray. There are numerous molds, some of which could take up residence on a Kombucha colony, but since the above two seem to be the most common culprits, there's really no need to bore you to tears with many paragraphs of mold identification and information . However, if you'd like to see that information in a future issue of this newsletter, please let us know and we'll include it.

Last summer (08-26-96) there was a discussion about mold on the Kombucha Mailing List/Digest. Here's a portion of that discussion:

From Chet in the U.K.

"I had a lot of mold on the surface, probably from using cheese cloth. Also there's a lot of mold in England, as bread doesn't last long in our house either. The question I have is whether it's worth drinking the tea when it has the moldy taste. It is drinkable because it's still relatively sweet. I didn't uncover the pot until after seven days, at which point I took out the thin new culture and rinsed it to remove the mold. But since it was only growing for seven days and it wasn't particularly warm, it may be that there isn't much of value in the tea. Any opinion?"

Response from Mike Roussin:

"As for my opinion; Chet, I wouldn't drink it. While you didn't identify the mold, most common are Penicillum notatum and Aspergillus niger (at least from what we've seen). While neither are pathogenic per se, some sub-species are. The ferment should be disposed of, and you should start with a new colony. Regular Kombucha consumers would notice first that there is no acetic acid in the ferment, which is one of the methods by which it protects itself. The musty flavor is nothing like the proper ferment, and while I've tasted moldy ferments (after testing them), it's pretty foul by Kombucha standards. The problem with molds is, you don't know what you have without sending it to a lab. Testing it on yourself is like playing mycotoxin roulette... one day you're going to get a bad one... and it won't take very much. It is the focus of every credible warning I've seen on the topic.
Michael Roussin

We hear from a lot of people who tell us that when they received their first Kombucha that the accompanying 'instruction sheet' advises that upon discovery of mold, just wash , scrape or cut it off and continue using the contaminated colony. In my personal opinion, this is appalling, and totally dangerous advice. Even more shocking is that some of this 'mis-information' comes from respected authors. Here's an excerpt from the book 'Kombucha - The Miracle Fungus' by Harold Tietze.

...."It is a little harder if the fungus has started to grow moldy. Too low temperatures or an unclean environment can be the cause. In this case, dispose of the beverage and wash the fungus as described above. (Clean, using lemon juice or wine vinegar). The usual 10% should be taken from another brew to start a new batch. It there are no other batches, put the fungus into the prepared tea with the required sugar content and add two tablespoons of vinegar (better still, Kombucha vinegar). The beverage should have a sour smell to it after a few days. This is an indication that the fungus is working. It should not have a moldy smell."

Here's another bit of bad advise from Christopher Hobb's book, 'Kombucha, The Essential Guide':

...."If molds form (often in the form of blue, green, red or black floating islands), discard the tea, and remove the Kombucha mother. Bring it under a cold water faucet; if the pellicle tears easily or seems to be disintegrating, throw it out. Otherwise, wash it carefully under cold running water, place it aside, and begin to make the tea again from scratch. Sterilize the containers by filling with boiling water, then washing. Some authors (de Silva and Saravanapavan, 1969) suggest that when a mother becomes contaminated with mold, one should wash it gently with water, rubbing it off with the finger, then rinse in pure apple cider vinegar."

What causes mold to grow on Kombucha? How can you protect your 'Kombucha family'? Here are some possible 'causes' and some prevention tips:


A good rule of thumb is to use the same hygiene you'd use when preparing formula for a newborn baby. Make sure all of your utensils and the work area have been washed with hot soapy water and rinsed well. If you have a dishwasher, this will make your job a lot easier.

If you (women) have acrylic nails or overlays, it would be a good idea to wear latex gloves. As you well know, a tiny little area can 'lift' and moisture can collect under the nail/overlay. What a great place for germs or mold. If you've ever suffered with the dreaded 'nail fungus' you know what I'm talking about.

Even if you do wear latex gloves, wash your hands (gloves on) before working with your Kombucha. A lot of the newer 'antibacterial' dishwashing liquids are good for this.

For men, and the lucky women with natural nails, scrub your hands with the antibacterial soap, using a nail brush and be sure to rinse well.

Keep the Kombucha work area free of dirty dishes, fresh fruit and vegetables from the market, potted plants, caged birds, and other pets. If you are called to the phone or the front door, be sure to cover the utensils and Kombucha colonies with a freshly laundered tea towel or paper towels until you get back.

If you can, try to use your stainless steel pot for boiling the water for Kombucha preparation only. This way you'll be absolutely sure that there's no microscopic bits of food left in that pan. Ditto for your ladles, spoons, strainers, etc.

If you use tea bags, it might be a good idea to use the more popular brand that sells well in your grocery store. If you see a box/can of tea on the shelf and it's dusty and has obviously been there awhile, you are asking for trouble. You have no way of knowing how many years - yes I said 'years'- that box of tea has been on the shelf. If the tea has been on the shelf for a year, the vitamins will have disappeared from the tea leaves, and I suspect that the polyphenols & catechins may also be affected. Remember that a beautiful label and lovely , descriptive words have nothing to do with the freshness of the tea you purchase. If, when you open the tea and it has an 'old or stale' smell, chances are, that's just what it is - old and stale.

Stick with the formula. At least until you are comfortable working with Kombucha. Don't experiment with 'chocolate/ambrosia' or 'fruity mango/watermelon/kiwi' flavored teas. After awhile you'll have some spare colonies in storage (large jar, loose lid, covered with tea) in the fridge. Then if you must have 'tutti-frutti / banana' flavored KT, try it then. And if it molds or turns out so yukky you can't stand it, you'll have a 'back-up' mom to start over with. Remember, the less expensive flavored teas are flavored with fragrance oils. This in itself could be a problem.

Probably the most important thing you can do to protect your Kombucha from mold is to be sure that you add enough 'starter tea' to the batch. The typical batch contains 3 quarts of water. That's 96 ounces. So, 1/10th of that would be 9.6 ounces of fermented KT added to the batch. Be on the safe side and add one and one half (1-1/2) cups of KT to your growing medium. As an extra precaution, do it this way: after you have placed the 'momma' in the cooled growing tea in the bowl/jar, pour the 1-1/2 cups of fermented KT over the momma. This will protect her from the 'get go'.

If you are using a cloth (tea towel, T-shirt, whatever) to cover your fermenting container, consider switching to paper coffee filters or paper towels. I have a hunch that many infestations of mold come from a cover cloth that has not been properly laundered, or from dust, etc., filtering down through the cloth during the fermentation time.

Ferment in a safe place. Try not to place the fermenting vessel on the floor, under the sink, in a shower stall, in the bathroom, in the laundry room, in the garage. Believe me, people do that! One of my clients found mold on his batch of Kombucha. When he called me about it, I asked the usual questions. When I asked 'where do you ferment?'. He said... 'that's it! I keep it on a shelf in the laundry room and my roommate is always tossing his dirty sweats and socks on top of it, and the dogs, three of them sleep in that room at night'. His problem was solved by moving the bowl to a non combat zone.

When you harvest your Kombucha, make sure that the plate or bowl you place the 'mom & baby' on is rinsed well with hot water. Use gloves. If you plan on cutting your Kombucha, be sure that you use a high quality stainless steel knife or scissors.

I have to gloat just a little (and knock on wood). In the six years I've been brewing Kombucha, I've never once encountered mold. So, I have to think that I must be on the right track when it comes to cleanliness and, especially, the addition of starter tea.

So, if it happens to you - don't waste a lot of time worrying about what you did wrong, where did it come from, etc., Just toss the whole mess out and start over, following the above guidelines. Chances are that if you encounter mold, the person you received your Kombucha colony from did not properly care for their colonies, and even though the colony appeared healthy, it was already contaminated with mold.

Harmonic Harvest Products

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