What is SCOBY in Kombucha and How is it Made? Complete Discussion Here!

• The Fermentation Process of Kombucha
• Factors Affecting Fermentation and Quality
• How is SCOBY Formed?

Kombucha is a fermented drink made from green or black tea, sugar, and a combination of bacterial and yeast cultures known as SCOBY (Symbiotic Culture of Bacteria and Yeast). It was first brewed in Northeast China in 220 BC, where it was discovered for its potential health benefits. The name “kombucha” is believed to originate from Dr. Kombu, a Korean physician who introduced fermented tea to Japan as a healing remedy for Emperor Inkyo. Kombucha gained popularity in the 1990s, driven by growing consumer awareness of its possible health benefits.

The Fermentation Process of Kombucha

Kombucha fermentation involves three main types of microbes: yeast, acetic acid bacteria, and lactic acid bacteria. These microorganisms interact in a mutualistic way, working together to produce the unique properties of kombucha. The fermentation process begins with yeast, which breaks down sucrose (sugar) into glucose and fructose. 

These sugars are then fermented, producing ethanol and carbon dioxide. The most common yeast species found in kombucha include Saccharomyces cerevisiae (high ethanol tolerance, fast fermentation), Zygosaccharomyces bailii (high osmotic and ethanol tolerance), Brettanomyces bruxellensis (converts sugar into ethanol and acetic acid), and Schizosaccharomyces pombe (produces polysaccharides and ethanol).

As the ethanol concentration increases, it promotes the growth of acetic acid bacteria, such as Acetobacter xylinum, Gluconobacter oxydans, and Acetobacter pasteurianus. These bacteria convert ethanol into acetic acid, gluconic acid, and glucuronic acid. A. xylinum is responsible for producing microbial cellulose and acetic acid, G. oxydans oxidizes ethanol into gluconic acid, and A. pasteurianus plays a role in acetic acid production. Additionally, lactic acid bacteria (Lactobacillus and Lactococcus) contribute to the increasing acidity of the kombucha by producing lactic acid.

Kombucha fermentation occurs in two stages: yeast fermentation and bacterial oxidation. In the first stage, also known as anaerobic fermentation, yeast breaks down sucrose into glucose and fructose, which leads to the production of ethanol and carbon dioxide, creating natural carbonation in the kombucha. 

In the second stage, or aerobic oxidation, acetic acid bacteria convert ethanol into various organic acids. This process requires oxygen, so the fermentation jar must be covered with a breathable cloth that allows airflow while preventing contamination. During this stage, a biofilm (SCOBY) forms on the surface of the liquid, trapping bacteria and creating a layer of microbial cellulose.

Factors Affecting Fermentation and Quality

Several factors influence the microbial interactions in kombucha fermentation, including pH levels, oxygen availability, sugar composition, and the type of tea used. At the start of fermentation, the liquid typically has a pH of 5 – 6, which gradually drops to pH 2 – 3 by the end of fermentation. This increasing acidity helps prevent the growth of harmful microbes and maintains fermentation stability. 

The availability of oxygen is also crucial for supporting the growth of acetic acid bacteria. The type of tea used also plays an important role in microbial activity. Black tea is recommended for kombucha fermentation because it contains polyphenols, which support microbial growth. The balance of microbial interactions determines the flavor, nutritional content, and health benefits of the final kombucha product. 

Yeast activity produces ethanol and carbon dioxide, giving the drink its natural fizz. Acetic acid gives kombucha its sour taste and acts as a natural antimicrobial agent. Additionally, the production of gluconic acid and glucuronic acid supports liver detoxification, while the formation of thick microbial cellulose serves as a protective barrier during fermentation.

How is SCOBY Formed?

One of the defining characteristics of kombucha fermentation is the formation of SCOBY, a jelly-like cellulose layer that develops on the surface of the kombucha. The formation of SCOBY begins with acetic acid bacteria, which produce microbial cellulose as a byproduct of fermentation. Over time, these cellulose fibers expand, forming a floating pellicle or biofilm. As fermentation progresses, the biofilm thickens and can be reused for future fermentation batches.

SCOBY plays several essential roles in the fermentation process. It acts as a physical barrier, preventing contamination from unwanted microbes. It also serves as a habitat for beneficial bacteria and yeast, allowing them to reproduce efficiently. Additionally, SCOBY enhances oxygen supply, which helps speed up the fermentation process and improves the overall quality of kombucha.

Get a deeper understanding of what goes on behind a cup of kombucha. Make sure your kombucha product is fermented with the right process and healthy microbes. Want to know how to test the quality of your kombucha? Consult our lab now.

Author: Safira Prisya
Editor: Sabilla Reza

References:

Troitino, C. 2025. Kombucha 101: Demystifying The Past, Present And Future Of The Fermented Tea Drink. Tersedia: https://www.forbes.com/sites/christinatroitino/2017/02/01/kombucha-101-demystifying-the-past-present-and-future-of-the-fermented-tea-drink/, diakses pada 6 Febuari 2025.

Villarreal-Soto, S.A., Beaufort, S., Bouajila, J., Souchard, J.P., Taillandier, P. 2018. Understanding Kombucha Tea Fermentation: A Review. J Food Sci. 83(3):580-588. doi: 10.1111/1750-3841.14068. PMID: 29508944.