Kombucha: quite easy to make, quite hard to understand

Making of... #2

A few days ago, I was at a friend's house and she was drinking kombucha, a fermented drink that is becoming quite trendy in France. And well, I had no idea how it was made ! Only that it was fermented.

So I decided to explore that this week and share the results with you on this Friday's newsletter article !

Basically, kombucha is a fermented and carbonated tea that can be left plain or can be flavored with different fruits. The making process is quite easy to reproduce at home - I’m sure some of you have already seen the hundreds of videos that are available on Youtube - you only need tea, sugar, an inoculum (the bacteria and yeasts that start the whole fermentation process - we will look further into this later on) and patience… a lot of patience ! The average duration of the fermentation is ten days, so don’t expect to drink your kombucha right away !

Here is an overview of the different steps. First, you need to make a sugary tea by warming up some water, brewing a dozen tea bags in it and adding sugar. The sugar will be the fuel of the fermentation, so there’s quite a lot of it initially but it will be eaten up as the fermentation goes on. Then, once the tea has cooled down to a room temperature (you don’t want to kill or freeze your bacteria !), you add what is called a SCOBY : a Symbiotic Culture of Bacteria and Yeast. This is basically an unappetizing blob containing all the bacteria and yeasts that you’ll need. Then you cover your jar with a cloth (the SCOBY needs to have access to oxygen) and you wait for seven to ten days.

After this first fermentation, you can add a second fermentation where you add fruit juice, herbs or spices to your batch of kombucha and put it into a closed glass bottle (while removing the SCOBY) for two more days. This is the process that will get you a nicely carbonated kombucha.

And that’s it ! That’s the fermentation of the kombucha ! Seems easy right ?

(Did you know this meme was originally made from a woman trying kombucha for the first time ?)

But understanding what’s going on inside the drink is quite complex for the scientists, mainly because the details of the fermentation process varies a lot from kombucha to kombucha. In fact, the final composition depends on the inoculum source, the sugar and tea concentration, the fermentation time and the temperature used.

What we do know is that this drink is made from the combination of mainly two different types of fermentation : alcoholic fermentation and acetic fermentation. This combination is due to the presence of different types of yeasts and bacteria in the inoculum.

The yeasts in the SCOBY transform the sugar into alcohol and some of the bacteria transform the alcohol into acetic acid (the same acid that is present in vinegar). That’s why, depending on when you stop the fermentation, you’ll have a drink with different alcohol and sourness levels.

In parallel, there are bacteria that transform the sugar into cellulose to form the biofilm (that’s the scientific name for the bacteria blob). As this process needs oxygen, the SCOBY will grow and form another layer only during the first fermentation.

During the second fermentation, some other bacteria will transform the acetic acid into CO2, increasing the carbonation of the kombucha. You need to be careful at this stage because while closing the bottle inhibit the formation of a new SCOBY (you really don’t want to drink that, ew), it will steadily increase the pressure in the bottle - as the bacteria keep creating more CO2. You’ll have to open the bottle once or twice a day during the second fermentation to avoid creating a bomb in your pantry.

Once the second fermentation is done, keep your kombucha in the fridge to pause its fermentation !

Traditionally, kombucha is made either from green tea or black tea but some persons use the SCOBY with other substrates than tea. I’m not sure it can be called kombucha then, but you can make your own little experiments with other liquids like coconut water, grape juice, etc !

Thank you for your attention ! Don’t hesitate to like, comment and share this article !

Source :

Jayabalan, R., Malbaša, R. V., Lončar, E. S., Vitas, J. S., & Sathishkumar, M. (2014). A review on kombucha tea—microbiology, composition, fermentation, beneficial effects, toxicity, and tea fungus. Comprehensive Reviews in Food Science and Food Safety, 13(4), 538-550.

Villarreal‐Soto, S. A., Beaufort, S., Bouajila, J., Souchard, J. P., & Taillandier, P. (2018). Understanding kombucha tea fermentation: a review. Journal of food science, 83(3), 580-588.