Fermentation of fungi

Kombucha is a fermented drink, which goes all the way back to ca. 220 BC in China. The drink is made from a sugar-containing tea, which is converted to kombucha by a special tea fungus called SCOBY. Kombucha is easy to make at home and is an exciting way to learn about fermentation. Hear about how to start brewing your own kombucha and learn what happens during the process.

Are you a high school student? Use kombucha for learning!

EXPERIMENT
ACTIVITY

This is what you need

Recipe (for 1 liter kombucha)

  • SCOBY culture
  • 1 dl starter liquid (ready-made kombucha)
  • 1 liter water
  • 90-100 g sugar
  • 5-7 g tea
  • A large pot
  • Fermentation jar (preferably with a nozzle for drawing off)

The amount can be scaled up to suit your needs!

What is a SCOBY?

SCOBY (Symbiotic Culture of Bacteria and Yeast) is what works wonders in the brewing of kombucha. SCOBY is made up of a large collection of different bacteria and yeast species, which live together in a symbiotic relationship on a large layer of cellulose. The largest component comprises acetic acid bacteria, which give kombucha its characteristic taste.

SCOBY is just as a sourdough — once you have it, you can continue using it for brewing kombucha. SCOBY grows rapidly and continually creates new layers over the top, and therefore you will soon find yourself with lots of SCOBY, which you can pass on to others.

How can I get hold of some?

Get your SCOBY from other happy kombucha brewers. We recommend you inquire in the Facebook group: Kefir og Kombucha DK (Alt Om Fermentering) (Everything about fermentation).
Or, order SCOBY over the net on, for instance, Amazon or eBay. You can also find a starter kit, which come with everything you need.

Procedure

1. Boil half the water in a pan and add all the sugar.

It can seem like a lot of sugar but much of it is taken up by the microorganisms and used to produce acetic acid and other organic compounds. The sugar serves as an energy source for the microorganisms, and therefore large amounts of it are needed.

2. Turn off the heat when the sugar is dissolved. Put the tea in a tea bag and place it in the pan. Leave it there for 15 minutes.

The most common type of tea is normally used, but you can experiment with other types of tea. Non-organic ingredients should be avoided, as some additives may be antimicrobial. Oil of bergamot in Earl Grey tea has also been shown to have antimicrobial activity.

3. Add the other half of the water cold and let the tea cool down to room temperature.

If necessary, add ice cubes to speed up the cooling process. The microorganisms cannot tolerate high temperatures and therefore it is important not to add them before the temperature has decreased.

4. Transfer the cold tea to the fermentation jar. Put the SCOBY in the jar together with the starter solution.

The starter solution helps avoid contamination as it contains the correct microorganisms and is acidic. When the microorganisms are in place in the tea they outcompete other undesirable microorganisms, particularly molds. Kombucha is self-preserving.

5. Cover the fermentation jar with a dishcloth and let the tea ferment (ca. 7-10 days).

Avoid completely closing the jar in order to create an aerobic environment in which the SCOBY can breathe. The dishcloth prevents flies and dirt from coming into contact with the kombucha. The process takes 7-10 days and the drink becomes more and more acidic the longer it is left. Taste the drink and draw it off when it is right for you. Once drawn off, the kombucha can be kept chilled to slow the fermentation process. Do not forget to retain the SCOBY and some starter solution for the next brew!

6. Secondary fermentation (optional).

Make your kombucha delicious by adding a natural sparkle. Pour the kombucha into a patented jar and close it to create an anaerobic environment. Let the kombucha ferment further at room temperature for 2-4 days. A little sugar may be added to ensure that carbonic acid is produced.

7. Add flavoring (optional).

Flavoring may be added to the patented jar during the secondary fermentation. Experiment with berries, fruit or spices (ginger is a winner!).