What is a Scoby? Presenting Kombucha Magic

Since getting into fermenting, I have learnt a lot about the practicalities of how to brew kombucha and what to do. I haven’t known ‘why’ you do something! Why is it that you shouldn’t really use honey over sugar in the first ferment? Or why may a small pellicle form in the bottle during the second ferment? At the same time, if you’re like me you may know that SCOBY stands for ‘symbiotic culture of bacteria and yeast’, but what does that actually mean? And, what is a SCOBY? In many ways, the SCOBY is similar to ‘the mother‘ in apple cider vinegar, but different in many other ways.

This article has been carefully constructed using various scientific journals and research papers to answer some of these questions. My goal is that by providing you with more of an understanding of ‘the why’, this will provide you with a bit more insight and understanding to ‘the how’. This will help make you a better brewer and produce better boochs.

Firstly – the basics

Kombucha is traditionally made through brewing black tea and adding sugar. Most commonly the teas used include assam, oolong and pu’erh, however there are many alternatives. These include green and white tea, hibiscus flower as well as my own experimentation with redbush tea. Other fermenting proponents are now pushing the boat further using ‘non-teas’ as their base. These may include coffee and Jerusalem Artichoke. The water that you use is also highly important as it can affect the ferment and taste.

Selection of kombucha using pu'erh, assam and hibiscus teas

Once the sweet tea mixture has reached room temperature, it is ‘infused’ with a previous batch of kombucha, and generally a gloopy mass of cells is added. Adding the previous ‘broth’ of ‘booch immediately lowers the pH (acidity) to approximately pH 4. This is the equivalent acidity found in a nectarine.

This immediately makes the tea a less attractive food source for harmful bacteria. This reduces the risk of it going off. It also gives the tea a bacterial boost to speed up the fermentation process. It is important to make sure that the tea has reached room temperature before adding your broth, to ensure that they aren’t killed off by high temperatures.

Several studies have been undertaken to determine what is the ideal length of time, amount of tea and sugar and the amount of broth that should be added. The general finding is that it is down to personal preference. However, understanding the chemistry of these processes will help inform your decision making.

So is the gloopy mass of cells the Scoby?

In short, no!

To cause the transformation of sweetened tea to kombucha the addition of this SCOBY is fundamental. So, what is the scoby?

When you first start brewing you will hear a lot of talk about the Scoby.

If like me when I started out fermenting, you’ll probably assume that the gloopy blob resembling a jellyfish is the scoby. Follow the reddit kombucha forum and you’ll hear lots of other people say that it is as well!

However this blob is actually the pellicle. In fact, the SCOBY is the ‘broth’ from the previous batch added to the sweet tea!

So is every SCOBY the Same?

Again, no!

One thing that is certain is that there is no consistent scoby that all ‘booch brewers use with the same ratios and types of bacteria and yeast. The only thing that is consistent is that there is always yeast and acetic acid bacteria. And did you know in fact, that lactic acid bacteria aren’t always present?

Some of the more common acetic acid bacteria include acetobactera, gluconobacter and
komagataeibacter; with some of the more common yeasts including candida, saccharomycoides, rhodotorulaspora, lachancea. Interestingly lactic acid bacteria isn’t always present, however when present, the most common strains are Lactobacillus, Bifidobacterium, and Oenococcus.

Putting the ‘symbiotic’ into symbiotic culture of bacteria and yeast

Symbiotic means “a mutually beneficial relationship between different people or groups”. For anyone familiar with the film ‘Finding Nemo’ you’ll know that the relationship between a clownfish (Nemo) and an anemone is symbiotic. The clownfish receives protection from the anemone, whilst the clownfish provides food to the anemone through the excretion of waste.

So what is symbiotic in the SCOBY?

Kombucha brewing usually follows the process shown in the image below and occurs due to a
number of biological reactions between the various yeasts, bacteria sugar and tea. The sugar is broken down by the yeast and turned into fructose and glucose. These are converted into alcohol through alcoholic fermentation. This then provides the acetic acid with carbon food sources that they can eat.

a cog and spoke imaging answering the question of is a scoby and the symbiotic relationships

With the mixture being in contact with air, the aerobic (oxygen loving) acetic acid bacteria use the
available glucose and ethanol (alcohol) to produce organic acids. These acids then reduce the pH of
the tea to about pH 3 (from the initial pH of 4). This helps prevent the growth of bad bacteria in the
tea which can cause it to spoil / go off.

the interactions between bacterias yeast and sugars are what makes a scoby a scoby

As part of the first fermentation; in addition to the scoby, the gooey blob ,that is the pellicle is usually
also added. This comprises cellulose which is produced by a specific aerobic acetic acid bacteria
called Komagataeibacter xylinus.

At the end of the first fermentation (F1) which takes approximately 7 – 10 days, the signs of a healthy brew are a growth in the pellicle and / or the growth of additional pellicles.

Removal of the Pellicle

Prior to bottling for the second fermentation (F2) the pellicle is removed.

Further growth of a pellicle is limited due to the lack of oxygen (although it does happen).

By removing oxygen and putting the mix into anaerobic conditions further acidification is limited. So the booch shouldn’t, get much more sour than how it tastes after finishing the first ferment. This also supports alcoholic fermentation by the yeast which contributes to the drink becoming fizzy.

So Scobys really are the symbiotic of symbiotic relationships

To truly understand what a SCOBY is, we must break down the process of kombucha brewing. A SCOBY, which stands for ‘Symbiotic Culture Of Bacteria and Yeast,’ is actually the ‘broth’ from the previous kombucha batch that kick-starts fermentation in the sweet tea mixture, rather than the commonly mistaken ‘gloopy blob,’ also known as the pellicle.

Its crucial role is transforming sweet tea into the fizzy probiotic-rich beverage we all love, kombucha, through a series of fascinating symbiotic relationships.

The yeast in the SCOBY breaks down the sugar into fructose and glucose, and then into alcohol. This alcohol then feeds the acetic acid bacteria, which in turn produce organic acids that lower the pH of the tea, preventing harmful bacterial growth.

The mix of bacteria and yeast within a SCOBY varies widely, with no standard blend used by all kombucha brewers, adding another layer of uniqueness to each brew. The better understanding you have of ‘the why’ behind the kombucha brewing process and SCOBY’s role in it, the better equipped you’ll be to master ‘the how’ of brewing delicious, healthy kombucha.