How To Tell If Your SCOBY Has Mold

It’s every brewers worst nightmare – peering in to check on your SCOBY only to find a fuzzy cluster of mold growing on top.

Many brewers aren’t sure of exactly what they are seeing so they upload panicked pictures to brewing groups.

Unfortunately, most new brewers overreact when they see their new SCOBY forming and immediately think it’s mold. In most cases, it’s not.

Usually, it’s just the new SCOBY forming on top of the liquid. But it can also be a host of other things such as kahm yeast or carbonation bubbles (covered below).

Every so often, however, it is mold. Which means the entire brew must be thrown out and started over. This article will show you the many faces of a healthy brew as well as exactly what mold looks like.

I’ll cover what you need to do when you find mold and how to make sure it never enters your brew again. Let’s get started by taking a look at some healthy brews.


The Many Faces Of A Healthy SCOBY

Over the years I’ve collected pictures of the different ways a kombucha brew can develop. Some pictures are from my own brews, some are from brewers I know personally, and others are from brewing groups I’m a part of.

However, they all have one thing in common – the kombucha is growing perfectly fine!

When you’re new at brewing you have no reference to what is normal. No reason why so many new brewers freak out when they see their new SCOBY forming.

Hopefully this helps. Below are a number of brews that are completely normal.

The Look Of A Developing SCOBY

Below are pictures of what a new SCOBY looks like during development. This is a common stage where people suspect mold as the SCOBY had a tendency to develop in little white dots.

For the inexperienced eye, this can look suspiciously like mold. But don’t worry, this is completely normal!

The white dots are just a new SCOBY forming
Normal development

As the SCOBY develops, these white patches will begin to connect – eventually forming a thin layer of SCOBY.

New SCOBY forming with yeast underneath

Kahm Yeast

One of the more disgusting looking SCOBYs are the ones that have developed Kahm yeast. While this doesn’t mean you need to throw the SCOBY out it does mean the taste of your brew may be affected.

Most people just try and scrap off the top layer of the SCOBY and continue brewing. However, if you have extra SCOBYs from your SCOBY hotel I’d recommend just starting over.

The taste will be slightly off and you don’t want to run the risk of developing Kahm yeast again.

Kahm Yeast (will discuss below)
More kahm yeast

Dark Yeast Strains

Another common mistake is to think that the yeast is actually mold. Depending on the age and the type of tea you brew with the SCOBY, and the yeast from the SCOBY, can have different colors.

Kombucha brewed with black tea tends to have a much darker colored SCOBY as well as darker colored yeast.

The yeast is usually hanging out at the bottom of the vessel, or on the bottom of the SCOBY, but it can also sometimes float to the top.

It doesn’t matter where the yeast is within the vessel. It’s fine if it’s near the top, or if it’s floated to the bottom. If it’s floated to the top, it can sometimes combine with the developing SCOBY to form what looks something like mold (see picture below.)

If you see something similar it’s nothing to worry about. It’s completely normal!

New SCOBY forming with yeast underneath

Bubbles From Carbonation

If your brew is healthy it will be producing lots of carbonation bubbles. Usually these bubbles just vent off without a trace. Occasionally, they can interact with the dark yeast to form small groups of foam.

This can occasionally look like fuzzy mold if they are small enough. They usually dissipate over time and are nothing to be concerned with.

CO2 bubbles
Bubbles and a new SCOBY forming
Not mold, just yeast and bubbles

I don’t blame people for wondering if their new SCOBY is actually mold – they can look similar. The may difference between normal SCOBY growth and mold growth is the fuzz.

Mold will have fuzz, yeast, kahm yeast, and regular SCOBY growth will not.

Sometimes, the old SCOBY will have plenty of leftover yeast from the last brew. This old yeast is often mistaken for mold when it floats to the top and joins with the new SCOBY. Yeasts can take many forms, some of which are not always obvious.

I find one of the best ways to understand when you have mold is to have a basic understanding of what it looks like. So, I’ve compiled a number of pictures from the same resources for your records.


Here’s What Mold Looks Like On Your SCOBY

Mold is actually fairly straightforward to diagnose. It’s going to have the same characteristics:

  • Fuzzy
  • Green, blue, black or a combination
  • Grows in small circles at first until it joins
  • Grows on the top of your SCOBY

Mold needs an oxygen supply to survive, therefore you won’t find mold growing on a SCOBY that has fallen to the bottom of your vessel (curious as to why your SCOBY sinks? Found out more here.)

Instead, you’ll find it growing on the top of your SCOBY at the surface of your brewing vessel.

Mold generally grows on brews that have been left alone for a couple of months, but it can also form in a matter of days if you’re unlucky.

Below are different pictures of mold. Notice how they all have one thing in common: fuzz. This is the key to knowing if your kombucha has mold or not.

Pro Tip

All mold on kombucha will have a fuzzy texture. This is the easiest way to distinguish possible mold from yeast.

While the mold won’t always be the same color, it will generally have a similar shape and texture.

A bad case of mold
Notice how the growth is fuzzy
Fuzzy patches
Up close view
Another bad case of mold

Mold can be different shapes and sizes – it all depends on how long you’ve left it to grow. But no matter the size, the remedy is always the same: throw out your kombucha and start again!


What To Do If Your Kombucha Has Mold

Unfortunately, there is no saving a batch of kombucha once it has mold on it. Some people may try to scrape the mold off if it’s small, but this only takes care of the mold that is visible to the eye.

By the time you can see the sporagnium (the fuzzy bits) the mold may have already made its way throughout the brew. It’s not worth testing your luck!

Here are the steps you need to take if you’re unlucky enough to discover mold in your brew:

  1. Throw out the SCOBY
  2. Dump any of the kombucha down the drain
  3. Thoroughly disinfect the brewing container and anything else that came in contact with the brew (spoons, funnels, bowls, etc.)
  4. Find out why the mold occured and take steps to make sure it doesn’t happen again
  5. Start a new brew

1. Throw Out The SCOBY

Don’t try and scrape or cut off any visible parts of the SCOBY to try and salvage it. Mold has what are called rhizoids which can penetrate far into the food you are eating.

The spores, which are visible to the naked eye, are only a small part of the actual mold.

This means your entire SCOBY, and any other SCOBY present in the brew, should be considered toxic and must be thrown out.

2. Dump Any Kombucha Down The Drain

For the same reasons as your SCOBY you are going to want to get rid of any kombucha in the brew.

The fungus from the mold will still be present in the kombucha and trying to reuse the brew will just result in another moldy brew.

Spores can be difficult to get rid of, especially those that can survive in the acidic environment of kombucha. Dump the SCOBY, dump the kombucha liquid, and move on to stage 3 – cleaning.

3. Deep Clean Your Brewing Equipment

In order to get rid of all of the mold spores you are going to want to wash everything thoroughly.

The exact advice on how you wash your equipment will vary from brewer to brewer. Some say to use hot and soapy water, while others say to only use pasteurized vinegar (the vinegar must be pasteurized in order to prevent vinegar eels!)

Some brewers even do both – washing first with hot and soapy water with a final rinse with vinegar.

The issue some brewers have with using soap is the antibacterial properties. Their thinking is as follows: “why use antibacterial soap when I’m trying to grow my own bacteria?”

They think you are only creating an uphill battle for your SCOBY if you use soap.

Personally, I’m fine with using hot and soapy water. It’s never really made a big difference for me and I just find it easier to use. Just make sure you thoroughly rinse everything before you start brewing.

4. Find Out Why The Mold Occurred In The First Place

This step is also important to making sure the mold doesn’t come back.

I’ve heard stories of people who repeatedly battled mold issues brew after brew. Don’t be one of these people!

There is a section below that will cover this step in detail, but here are the basics:

  • Ensure your brewing vessel is covered
  • Keep your vessel away from sources of mold such as an open garbage can or a fruit bowl.
  • Ensure you are using the correct ingredients (most importantly – acidic starting liquid and a healthy SCOBY)
  • Ensure all your brewing equipment is clean before use

5. Start A New Brew

Don’t feel discouraged if you have a case of mold. It’s not always necessarily caused by a mistake in the brewing process – it may just be bad luck!

Just follow the above steps and try again! You’ll be up and brewing again in no time.


How To Prevent Mold In Kombucha

There are a number of different causes of mold. Sometimes it’s an overly humid environment, while other times it’s an unlucky cross-contamination from other mold sources in your kitchen.

Either way, your kombucha should naturally be able to fend itself off from mold. This means, if you have mold you may have missed an important step of the process.

1. Make Sure Your Starter Liquid Is Kombucha Vinegar

The first place you need to consider is your starter liquid.

For a gallon batch brew you need around 2 cups of low pH starter liquid. Ensuring the starter liquid has a low pH is crucial for the protection of your brew.

Not allowing your starter liquid to turn to kombucha vinegar is a common mistake new brewers make. Not only will this negatively impact the brewing process, it’s also a likely culprit of mold.

Pro Tip

Make sure your starter liquid has turned to kombucha vinegar before each brew!

This low pH starter liquid is required to create an environment that is inhospitable to foreign bacteria and fungai. Because your brew is going to be diluted by the addition of the sweet tea you need to make sure it’s extra strong before you dilute it.

For most people, the easiest solution is to take the starter liquid from the SCOBY hotel. This liquid, as long as you are feeding your hotel every so often, will always be ripe with healthy yeast, bacteria, and the acids required to lower the pH.

If you don’t have a hotel, try waiting a few extra days with your SCOBY in the brewing vessel with your starter liquid in order for it to turn to vinegar.

If you immediately start a new brew without waiting it’s likely your starter liquid was not strong enough.

This is also a common culprit of carbonation issues.

The acidic environment will kill any spores or foreign bacteria that happen to land in your kombucha while it’s brewing – thus becoming the last defense against mold. Don’t skip this step!

What If You Don’t Have The Right Starter Liquid?

If you aren’t able to secure kombucha vinegar for your starter liquid then you are going to want to use a higher portion of regular starter for your brew.

Instead of using only 2 cups, use 4.

This will help bring down the pH level of the brew closer where it needs to be.

2. Your Kombucha Vessel Should Be Covered With The Right Material

Ideally, we’d be able to seal off the kombucha brew completely from the surrounding environment. This way, no mold spores would be able to enter the batch.

Unfortunately, the kombucha development requires oxygen in order to thrive. This is why we choose vessels with wide openings and use cloth covers.

The bacteria need oxygen during the aerobic stage of fermentation in order to produce the healthy acids that lower the pH. Sealing off the vessel will stifle this acid production, in turn harming the yeast.

But this doesn’t mean you should leave your brewing vessel completely open to the surrounding air!

Instead, you should be using a tightly woven cloth that will both allow the air flow while filtering out any mold spores.

This is the reason why using cheesecloth isn’t the best option. The mesh is too loose to filter out mold spores and can even allow fruit flies to pass through and land on your SCOBY.

Pro Tip

Avoid using cheesecloth for your covering. Instead, use a tightly woven dishcloth.

3. Keep Your Vessel Away From Sources Of Mold

Another key component in preventing mold is keeping your brewing vessel away from other sources of mold. Some common sources are:

  • House plants
  • Open garbage containers
  • Fruit bowls

The less you expose your vessel to mold spores, the less chance you will have of growing mold.

Now this doesn’t necessarily mean you need to lock your vessel away in the cupboard (in fact, I don’t recommend you keep your vessel in the cupboard as it restricts the airflow.)

It just means you should avoid placing your brewing vessel next to a fruit bowl or open garbage can.

4. Using Flavored Teas or Fruit In Your Primary Ferment Can Sometimes Lead To Mold

As you know by now, regular kombucha is not a friendly place for mold spores. If your pH is low enough and your SCOBY healthy the chances of growing mold is very rare.

Things change when you start adding foreign ingredients to your primary ferment (the stage where you’re brewing in your brewing vessel.)

The bacteria and yeast in your brew need the right environment (more on that below) as well as the right nutrients in order to thrive. And when your bacteria and yeast thrive, the mold will not.

The tea you use in your primary ferment should be one form or another of Camellia Sinensis.

In other words, should be either:

  • Black tea
  • White tea
  • Green tea
  • Oolong tea
  • Pu-erh tea

These teas will provide the right nutrients and minerals required for your kombucha to thrive. You can find out more about the best teas for kombucha in my article here.

If you want to use a flavored tea, you can add it to the second ferment stage.

I’d also recommend adding the fruit to the second ferment (F2) and not to the primary ferment if you are having mold issues.

I remember one brewing friend who always ended up with mold when she added berries to the primary ferment. Fruit can bring unwanted mold spores into the vessel. They are also prime places for mold to grow and develop.

5. Make Sure Your Brew Is In Its Optimal Environment

Another friend of my who brews in Singapore was constantly having mold problems. Her brew was always surrounded by a very humid environment which is very prone to growing mold.

I’m not suggesting that you cannot brew kombucha in a humid environment, only that this may be a key factor in why you are having mold problems.

If you are having mold, make sure your brewing environment meets the following criteria:

  1. Lots of airflow
  2. Temperatures around 68-78°F
  3. Away from sunlight

While the above points don’t all prevent mold, they do help maintain a healthy brew. A healthy brew is your best defense against mold.

This also means you may want to try and use a base heater, or non-LED Christmas lights for your brews during the winter months. This helps keep the temperature in the “happy” range.

6. Keep Your Workstation Clean

The cleaner your workstation, the less likely it is you will end up with mold. This applies to everything your brew will come in contact with.

Including your hands, brewing utensils, where you’re going to place your SCOBY, your brewing vessel itself.

This one just requires common sense. You’ll know what needs to be cleaned and what you can ignore.

Conclusion

Mold is actually very rare. You have to be pretty unlucky to have it once, and even more unlucky to have it twice.

If you have a constant mold problem that means there is something going wrong with your brewing method. Review what I suggested above, and if it still continues you can send me an email.

If you’re just starting out, I wouldn’t stress out about mold. Just make sure you follow what I suggested above and you will likely never see mold during your brewing career.

Good luck and happy brewing!

2 thoughts on “How To Tell If Your SCOBY Has Mold”

  1. my scoby had a green/ brown oblong 1″ long and 1/4″ substance under my scoby. was not dry or fuzzy and wiped off easily . would this be mold and do I have to through out my tea and scoby.

    • Hi Diane,

      By the sounds of it, my guess is that’s just yeast – it’s perfectly fine, you don’t have to throw out your tea. As long as it’s not fuzzy it’s probably not mold. Yeast can clump up and a layer of SCOBY can form over it making it look strange.

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