What to Do If There is Too Much Fizz in My Kombucha

My Kombucha Is Erupting And It Tastes Bad! 

While a good dose of fizz can make a batch of Kombucha very pleasant and delicious, extreme amounts of carbonation, combined with an overly sour flavor, is an indication that something is wrong with your SCOBY / Kombucha brew. Usually this scenario is also accompanied by a malformed SCOBY (For more info on the signs of a malformed SCOBY, check out What Does A Healthy Kombucha SCOBY Look Like?).

The main cause of excessive carbonation and an overly acidic brew, is an imbalance within the SCOBY culture between the yeast and bacteria population. Now you are probably thinking to yourself, well what do I do, I can’t even SEE the microbes, let alone get down there and balance them! But don’t panic, there are a few sure fire ways of rectifying the issue.

First I will explain a bit more about the SCOBY yeast/bacteria balance, so that you can get a picture of what’s going on before proceeding ahead with the treatments.

The SCOBY Balance

The Kombucha SCOBY is a symbiotic colony of species of yeasts and bacteria. The two different populations work in conjunction with each other, and each requires the other to function properly within the culture. If either of them becomes dominant the overall SCOBY health suffers.

Stored SCOBYs or recently purchased ones tend to have slightly stronger bacteria to yeasts ratios. This is caused by two reasons, one because the yeast species are in a dormant state, and two is that the SCOBY has not had the chance to be colonized by the airborne species of yeasts which become part of the SCOBY’s population when it is exposed to air during fermentation. This will usually result in a low level of carbonation. If you are experiencing this, and wish to up the carbonation, have a look at What to Do If There is No Fizz in My Kombucha (No Fizz).

However, after successive batches a more common problem is the opposite scenario, where the yeasts have now grown stronger and are out numbering the bacteria. This is the main cause of overly high levels of carbonation, and a very acidic tasting brew.

Overabundance and imbalances of yeast populations within SCOBYs are most common in tropical and warm weather climates. If you reside in a warm place like I do, then check out this guide to Warm Weather SCOBY Care: Brewing Kombucha in Hot Weather.

What Is Going On Inside the SCOBY

When the yeast population within the SCOBY gets out of hand and dominates the bacteria portion, what happens is that the yeasts go into a mode of respiration rather than fermentation. During the Kombucha brewing process – if proportions and conditions are right – the yeasts respire briefly and then go into fermentation mode.

During fermentation mode, the yeasts produce alcohol and small amounts of carbon dioxide. This is of benefit to the bacteria, as they feed on the alcohol. During respiration mode however, the yeasts produce high levels of carbon dioxide, and burn up available oxygen and glucose at a rapid rate. This cripples the bacteria, as not only do they not have any alcohol to feed on, they also have very little oxygen and glucose available to them.

In these conditions SCOBY growth will be extremely slow, and the brew will take on a sour acidic taste very quickly. Not to mention an overabundance of bubbles!

But don’t lose hope, and don’t throw out your SCOBY, here’s what to do.

Encouraging The Bacteria to Yeast Ratio

There are a few tried and tested methods of bringing the yeasts back to a normal level, and encouraging the bacteria. The aim is to get the yeasts into fermentation mode as quickly as possible, in order for them to start supporting the bacteria once more, rather than competing with it.

1. Temperature Control

If possible get your batch going and keep it at or below 73^o Fahrenheit (22^o Celsius). Good ferments are possible at 65^o Fahrenheit (18^o Celsius), but will take up to and above one week longer to mature.

2. Adding Glucose

Perhaps the best and most reliable way to manipulate the yeasts into entering fermentation mode rather than respiring, is to replace a portion of your sugar with glucose. Karo and corn syrup are good sources of glucose to use. Corn syrup is generally preferred among Kombucha makers. This strategy is known amongst beer brewers as the “Crab Tree” effect, where additional glucose pushes yeast prematurely out of the respiration stage and into fermentation.

3. Decreasing Tea Strength

If you are making medium to strong teas to start off your batch, it might be a good idea to weaken the brew. Reducing the tea strength lowers the levels of nutrients available to the yeasts. This means that they won’t have such a quick start, and providing they go into fermentation mode, will give the bacteria a gap to get going too.

Note If reducing tea strength, it is also advisable to use the ‘adding glucose method’ as well. What happens when the yeasts have less nutrients from the tea available to them, is that they end up producing fewer enzymes – the guys who are responsible for turning the sugar into glucose, which is required by the bacteria to feed on! So be sure to use both methods in conjunction, to ensure best effects.

The SCOBY Yeast Reduction Treatment Tutorial

If you feel that your SCOBY has an extreme case of yeast imbalance and the overall health is weak and the first 3 methods above are not enough, then here’s how to fix your problem via the Scoby Yeast Reduction Treatment.

Step 1

Start with a new batch of Kombucha. Pour into a new clean fermenting jar, ensuring that you have at least four inches of liquid, and leave to continue fermentation for 3 weeks.

Step 2

After 3 weeks have elapsed, remove the new SCOBY which has formed and filter the liquid through a coffee filter or paper towel. If you can find a way to siphon off just the top portion of clear liquid, this is even better as the lower portion is where the free floating yeasts will deposit. However if this is not possible, don’t worry about it as by the time 3 weeks have elapsed most of the yeasts have died off or gone dormant.

Step 3

Rinse and wipe clean the fermenting container.  Pour back the filtered liquid into the container and leave for another plus/minus 2 weeks, or until the SCOBY culture has reached a ¹/₂ inch (12cm) thickness.

And Voilà! You are now ready to start fermenting with your new super race of bacteria and yeasts. However, to ensure that the balance does not tip back to an overpopulation of yeasts, follow these methods when brewing your next batches.

Use liquid from your “master race” solution for the first brew. This will be very acidic, so use quite a bit less. After the first brew, use liquid from your SCOBY hotel. If you do not know about SCOBY hotels or wish to know how to store extra SCOBYs have a look at How to Create a Kombucha SCOBY Hotel (to Store Extra SCOBYs).

• Ensure that you are taking starter from the top of the SCOBY hotel or master race brew, because this liquid will contain fewer free floating yeasts.
• Keep brewing temperatures below 75^o Fahrenheit (24^o Celsius). Ideal fermentation temperature for already balanced cultures is 73.5^o Fahrenheit (23^o Celsius).
• Squeeze out the liquid from any unwanted cultures which you are discarding into the new ferment or into your SCOBY hotel where you store your extra cultures.
• Practice using a combination of glucose and sugar in your sweet tea starter. A ratio of 1 to 7 glucose to sugar is advisable.

 In addition, Green tea is considered to encourage a balanced and healthy SCOBY. It is also thought to produce a higher amount of the health giving organic acids. However, green tea can be expensive in some countries and also tends to give the finished brew a stronger tartness which some people do not like.

What one can do if concerned about the cost or taste, is to do a mixture of green and black tea. This produces nice results, and a more mild flavor. For more info on different teas one can use for Kombucha, you can also read What is the Best Tea For Brewing Kombucha.

Which Treatment Should I do?

If you are unsure whether or not you need to go through with the yeast reduction treatment tutorial, and do not want to wait so many weeks for your next batch, try out the first set of methods and guidelines with your new SCOBY. At the same time, take the old SCOBY – or one in storage in your SCOBY hotel, whichever looks healthier – and put that one through the master race process.

That way you will be able to enjoy making more Kombucha, and test out the yeast reducing methods, while waiting for your super strong, and newly balanced SCOBY to finish its’ treatment time.

I hope this has been of help, shed some light on the goings on within your Kombucha, and that your SCOBY culture is returning to optimum health. Long Live your SCOBY! : )