My SCOBY Is Sinking – What’s Going Wrong?

There are a few common questions that are asked within the kombucha groups I’m a part of. One of the most common is – my SCOBY is sinking, is this bad? Let’s answer this question once and for all.

There is absolutely nothing wrong with your SCOBY if it sinks to the bottom of your brewing vessel. SCOBYs have a mind of their own and will often do funny things during the brewing process. I’ve even seen a SCOBY hang out sideways in the middle of the vessel for a number of days. The fact is, your SCOBY will likely rise to the top after 4-5 days. Even if it doesn’t, that’s okay too!

The actual shape and position of your SCOBY actually doesn’t matter that much. People are usually surprised when they learn it’s possible to cut a SCOBY into pieces and it will still brew a perfectly fine kombucha.

What’s important is the yeast and bacteria that come along with the SCOBY, not the shape or position within the brewing vessel. Your mother SCOBY will still develop a child at the top of the vessel.

With that said, I’m sure some of you are still curious as to why the SCOBY sinks in the first place.


Why Is My SCOBY Sinking?

There are a number of theories as to why the SCOBY sinks in the first place. Some of them hold more salt than others. They are:

  1. The temperature of your new kombucha batch is different from the starter liquid
  2. There isn’t enough CO2 being produced to elevate the SCOBY
  3. The CO2 that has been trapped within the layers of the SCOBY has been released

To understand why a SCOBY sinks we first need to understand what keeps it up in the first place.

Because SCOBYs are denser than kombucha, they have a natural tendency to want to sink to the bottom. It’s the production of CO2 from the fermentation that keeps them afloat.

There are two stages to brewing kombucha:

  • Aerobic Fermentation
  • Anaerobic Fermentation

During the aerobic fermentation, the brew is allowed to breathe (this is why we choose the right brewing vessel with a wide mouth opening) and the bacterial culture begins to weave the new web of cellulose to form the child SCOBY.

During the second stage of fermentation, the anaerobic stage, the new SCOBY cuts off the oxygen supply to the brew and the yeast begin producing ethanol and carbon dioxide (CO2).

It’s this CO2 which keeps the child SCOBY and the mother SCOBY afloat.

Does the Temperature Of My Brew Make My SCOBY Sink?

Some people have suggested that the reason your SCOBY sinks is because your new vessel temperature isn’t the same as your mother SCOBY’s original temperature.

Technically, this isn’t true.

The temperature of the vessel doesn’t directly impact the location of your SCOBY. While a lower temperature will affect the density of the liquid, the density of the kombucha will actually decrease relative to the SCOBY – suggesting the SCOBY should float.

But, the density change of a few degrees isn’t large enough to cause the SCOBY to float or sink.

What temperature does do is affect the yeasts production of CO2. The higher the temperature, the more ethanol and CO2 will be produced.

Fun Fact

The temperature of your brew will also affect the length of your brew. This is the reason why brewing kombucha in the winter months takes a few extra days compared to summer. The temperature also plays an important role in how much alcohol is produced in your brew – find out more here.

So, matching the temperatures of your different vessels won’t prevent the SCOBY from sinking. What about the CO2?

How CO2 Lifts Your SCOBY

As the yeast near the bottom of the vessel begin to enter anaerobic fermentation, they begin producing more and more CO2.

These CO2 bubbles will eventually lift the mother SCOBY off of the bottom of the vessel and raise it back to the top.

When you first place your mother SCOBY into the vessel the yeast hasn’t had a chance to produce any CO2 so the SCOBY will sink. If you wait 4-5 days you’ll find the SCOBY will again float to the top.

Why Some SCOBYs Float While Others Sink

SCOBYs grow layer by layer. If your SCOBY is growing in an environment with plenty of CO2, some of these CO2 bubbles will become trapped within the new layers of SCOBY.

This is why some SCOBYs always seem to float – they have plenty of CO2 trapped within the layers of the SCOBY.

I find that older and thicker SCOBYs tend to float more often than new SCOBY, although this isn’t always the case. With time, some of the CO2 in older SCOBYs may diffuse out, resulting in a ‘sinker’ SCOBY.

If your SCOBY is new, it may not have had enough time to trap the required amount of CO2. So when you place it into an environment that lacks the CO2 required to lift the SCOBY up, it will probably sink.


Do I Need To Do Anything If My SCOBY Sinks?

Some people ask if they need to try and rescue the SCOBY. The answer is – no!

Your brew will develop a new SCOBY in the same time period if your SCOBY remained floating. Everything will be business as usual.

There is no need to try and raise the temperature of the brew, or worse, dip your hands into the brew to try and pick up the SCOBY.

The more often you touch your brew the greater chance you’ll introduce contaminants into the vessel (with a small chance of introducing mold.) Just let the SCOBY do its thing and don’t spend time worrying about it.

The only time you want to try and play with the temperature is when your brewing times are taking longer than the average 7-8 days. The optimal brewing temperature is around 75-80° Fahrenheit.

Pro Tip

A sinking SCOBY is not a sign that your brew temperature is too low.

Why Does My SCOBY Drop Over Time?

Some peoples SCOBYs start out floating, and then drop as the brew progresses.

This is, again, due to the yeasts production of CO2.

Yeast produce the most yeast in higher temperature. A sudden temperature drop may result in the yeast producing less CO2. This may cause the SCOBY to drop over time.

The SCOBY may also drop to the CO2 diffusing out of the layers within the SCOBY. Placing the SCOBY in a CO2 deprived environment would allow the CO2 to diffuse from the SCOBY which would cause it to sink to the bottom of the vessel.

The good news is, neither of these cases are cause for concern. Just continue on your normal brewing procedures and remember that SCOBYs have a mind of their own!


Conclusion

A sinking SCOBY is nothing to worry about. You don’t have to make any changes and your brew will be completely fine.

Some SCOBYs sink, while others float, there is nothing to be concerned about. No need to rescue the SCOBY or change the brewing temperature.

Wait a few days and you will see a new SCOBY forming and the mother SCOBY may even float back to the top.

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