If you’re new to brewing kombucha, you may experience a moment of panic the first time you see a SCOBY sink to the bottom of the fermentation vessel. What this means and what to do from here is, hands down, the most commonly asked question among new brewers. It comes in a few different variations but usually goes something like this:
If this sounds familiar to your own experience, rest assured that a sinking SCOBY is a common occurrence, and there’s no need to panic – it’s completely normal! The position of the SCOBY pellicle doesn’t matter during the fermentation process. So don’t use its location as a gauge of your kombucha’s health. Again, the placement of the SCOBY should never be used as an indicator of the health of your kombucha batch. Your SCOBY may sink, float, or hover in the middle; pay no mind. When you add your SCOBY to the brew, beneficial bacteria and yeast spread throughout the liquid and start the fermentation process. In time, a new SCOBY will start slowly forming on the surface and thicken over time. So rest assured, a sinking SCOBY is nothing to worry about!
Now that we’ve debunked the SCOBY position myth, you can celebrate knowing your batch is healthy! If you’re still curious about why some SCOBYs float while others sink or hover, read on for some insight.
There are a couple of key factors that impact whether a SCOBY pellicle floats or sinks: the first, is the scoby itself, and second, is density of the sweetened tea during fermentation. Both are forces of physics rather then signs of a healthy brew.
As mentioned earlier, each SCOBY is one of a kind when it comes to density, and thickness, which determines whether it will float or sink. Its weight, shape, and structure all influence its buoyancy. It’s worth noting that no two SCOBYs are the same, so some will float while others sink in your fermenting tea. These microbial mats are made up of a complex network of cellulose fibers, and the thickness and density of this structure can vary greatly from one SCOBY to another. Consequently, some are more likely to float on the liquid’s surface, while others, due to their denser and heavier nature, will sink straight through the tea, settling at the bottom.
Let’s discuss viscosity. Viscosity is a measure of how thick a liquid is. A liquid with high viscosity is thicker and has more resistance to flowing freely than a liquid with low viscosity. Think about honey and water – honey has a higher viscosity, so it pours or moves more slowly than water. In addition, things are much more likely to float on top of honey than water. So now let’s apply this idea to kombucha and how the viscosity of the sweet tea helps play a key role in whether a SCOBY will float, sink, or hover.
At the beginning of the kombucha-making process, the sugar you added is dissolved into the tea before adding the SCOBY. This means that at the start, the liquid will have its highest sugar content and will be at its thickest consistency. The added sugar makes the liquid heavier than regular water, and this can be measured using a hydrometer (click here to learn more: What is a hydrometer?). When you introduce the pellicle into this sugary environment, the liquid is at its densest; and depending on the density make up of your unique pellicle, it may sink or float initially. As we’ll explore next, the viscosity of the liquid will change and can result in the pellicle sinking if it started off floating.
Once you add your kombucha culture, fermentation is officially underway. During fermentation, yeast will steadily consume the sugar in the tea mixture, which is then converted into two byproducts: alcohol and carbon dioxide (CO2). This act of converting sugar to alcohol decreases the liquid’s density, which can influence the position of the scoby throughout fermentation. Consequently, as the thickness of the liquid changes, the scoby position throughout the brew jar can shift around.
As mentioned above, another important byproduct of yeast fermentation is CO2, which can also influence the movement of the SCOBY in the fermentation vessel. As CO2 bubbles are created, they rise to the surface and escape into the air. However, sometimes, the bubbles get trapped around the SCOBY or push through it, which can cause the SCOBY to move around in the jar. As the bubbles rise and escape, they can bump into the SCOBY and push it around in the liquid, much like a leaf being carried along by a stream.
If you notice that the SCOBY is initially moving around a lot, but then stops, it could be a sign that fermentation is entering the tail end. The fermentation timeline can be described using a bell curve, with a gradual and steady rise followed by an equally gradual decline. As the yeast consume the available sugar, it steadily transforms the liquid into kombucha, but as the sugar gets depleted, fermentation slows down. This same pattern is observed in the production of CO2 during fermentation. As the yeast consumes more sugar, it generates increasing levels of CO2, but as the sugar runs out, the production of CO2 gradually declines. This fluctuation in CO2 levels can make the SCOBY move in the fermentation vessel.
If your SCOBY starts off floating, but sinks part way through the fermentation period, it could be due to the changing density of the liquid as the sugar gets consumed, a decrease in CO2 production due to a drop in temperature, or fermentation winding down. The ideal temperature for fermenting kombucha is around 75-85F, that is when the yeast thrives and is most proactive. If the temperature of your kitchen drops below productivity temperatures, it will cause the yeast to become less active. Less productive yeast produces less CO2, thus one less force keeping the SCOBY afloat. Now, this still doesn’t affect the health of your kombucha; it’s just less productive, meaning the fermentation will take a little bit longer.
As temperatures become colder, yeast slows down as a means of energy conservation. In your kombucha brew, however, they have plenty of sugar to feed on. They will eat the sugar; it’ll just take them longer to do so then at, say, 80F. If your kitchen is naturally colder, I would maybe recommend buying a kombucha warmer to snug around your kombucha to help it along a little bit.
Now that you have a better understanding of the fermentation process and how the SCOBY behaves, you know dropping a dense SCOBY into a new batch of kombucha will most likely result in a sunken SCOBY rather than a floating one. This is simply due to the weight of SCOBY vs the weight of the tea above it.
More importantly, we know none of this matters when it comes to the health of the batch of kombucha. All that matters is that the tea gets inoculated with the bacteria and yeast cultures, and fed sugar. The sugar in the tea provides the necessary fuel for the bacteria and yeast to reproduce and create a thriving community of microorganisms, which is essential for successful fermentation. As long as the fermentation process is proceeding as it should, there’s no need to worry if your SCOBY sinks.
Now that we got that out of the way, it’s time to start thinking about the flavors you want to add to your kombucha. The secondary fermentation phase is where the fun begins! You can add all sorts of delicious flavors to your kombucha to create unique and tasty drinks. To get started, be sure to check out our kombucha flavoring section for flavoring ideas, recipes, and inspiration. From fruity and sweet to herbal and spicy, the possibilities are endless! The question is, what will you create?”
